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tunnelrider
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That good old hanging rpm topic again
08/29/17 at 15:14:54
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Hi all, yes I know this same topic has been covered many times (and maybe very recently by BPT) and I have searched and read a couple of posts on this subject so I do feel I've got a good handle on what the problem is, just want a second opinion I guess.
The problem is: While cruising at 4000rpm, if I back off the throttle completely then pull in the clutch lever (actuate the clutch) it takes approx 5 seconds for my revs to drop from 4000 rpm back to idle, approx 1000 rpm.  This has been happening to a lesser degree for a few years but I've just done a timing chain job and it's gotten a little more noticeable.  I'm thinking the ATU (bean can) springs are to blame.  While the ATU was off the bike for the timing chain job I opened the oval plate, saw the springs were pulling the weights to a stop and they seemed to be ok.  Gave a good squirt of CRC5-56 and squeezed in a little light oil.  But symptoms still persist.
- I have adjusted idle speed after a good 20km run to 1000rpm.  Throttle stop screws can be adjusted still. Slack in both throttle and choke cables.
- Idle mix screws adjusted out past what I have normally run at. (Makes no difference at normal or adjusted out further)
- Valve clearances just done
- Timing light shows advance starts approx 1500rpm and stops at approx 3000 rpm
- No air leaks at carb. manifolds
- Clutch drag technique brings idle down faster and idle stays down.

I guess the only two things I think it could be are either stretched/weak ATU springs, or a problem with the carbs, which are one of the few things I haven't had to pull apart yet as I've had no problems with them.

Have I missed something obvious?  Looking at descriptions of pulling the bean can apart it looks a bit tricky, but I believe I could do it ok.  The bike has 115K miles on it and I'm not sure if work's been done on the ATU previously.

Cheers.
P.S. I've just noticed that Barry's posts say he's now an ex member, could I just say that the asylum has lost a truly knowledgeable and kind hearted guru, cheers Barry!
« Last Edit: 08/29/17 at 19:49:47 by tunnelrider »  

 1985 Black R65  -  2001 DRZ400 dirt only
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Re: That good old hanging rpm topic again
Reply #1 - 08/29/17 at 19:45:53
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Holy crap, what happened to Barry??????

Mine was slightly different, at least when I noticed it.  My problem came up when I was coasting to or came to a stop. I'd let off the throttle but it would continue to rev above 2000 rpm.

With my newest problems (possibly ignition related), I've had the been can off.  My local guy was confused as to which one I had and told me to bring it in and they would check it out, expecting points or a variant of those.  I told him I didn't think that's what I had but........   I took it in and he struggled with getting it apart then the old timer there told him they rarely did because it's such a pain.   There are pictures and write ups online and I'm sure the experienced ones here can advise.  I'd say make absolutely sure you need to open it before you do.  For one thing, you have to pound a pin out to get to the inner guts.  Not quite as simple as unscrewing things and just trying to keep them in order.
  

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Re: That good old hanging rpm topic again
Reply #2 - 08/29/17 at 19:51:54
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BTW - I'd mentioned in one of my recent posts that the shop told me I needed my timing chain done and that I probably shouldn't wait as long as I thought I could.  They also told me that could be the source of my idle problems.

Since you say you just did yours, that shouldn't be it?  They told me with mine, kind of like needing the valves adjusted properly, that if the timing chain and/or tensioner is really worn, I'll never be able to get things adjusted correctly.
  

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tunnelrider
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Re: That good old hanging rpm topic again
Reply #3 - 08/29/17 at 20:07:20
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BPT wrote on 08/29/17 at 19:51:54:
BTW - I'd mentioned in one of my recent posts that the shop told me I needed my timing chain done and that I probably shouldn't wait as long as I thought I could.  They also told me that could be the source of my idle problems.

Since you say you just did yours, that shouldn't be it?  They told me with mine, kind of like needing the valves adjusted properly, that if the timing chain and/or tensioner is really worn, I'll never be able to get things adjusted correctly.


No I think if your idle is bouncing up to 2000 rpm again from lower revs then the carbs aren't adjusted properly, usually from doing them before the engine is truly hot. IMHO usually the throttle stop screws would be set too high.  Worn timing chain, or more correctly worn crankshaft sprocket and chain, presents itself as an unsteady, occasionally fluctuating idle rhythm but idle speed is still able to be adjusted to the correct range.  It also causes double (or blurred) images with a timing strobe light aimed through the timing plug hole.

Another reason for you is your ATU/bean can springs might not be bringing the wights back to the stop position.  You can check for this with someone's help.  Get them (or you) to aim the timing light while you have the bike at the high idle, then with the front or back brake on, let the clutch bring the revs down.  If the timing light shows the advanced position still (or at least not back to 'S' non advanced position) then the problem is your bean can/ATU.  Sometimes turning off the bike then restarting it will be enough for the high idle/stuck weights to return to the stopped position/ lower normal idle speed.
  

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Re: That good old hanging rpm topic again
Reply #4 - 08/29/17 at 20:49:21
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I just got my box from EME so will be installing the new coil, wires, etc. tomorrow. Since I've had the bean can off it will most likely need to be timed and the shop will do that for me.

As far as the carbs. I've had them adjusted numerous times.  The first time it happened I'd just come off of a highway ride.  I'd taken the exit and it happened at the stoplight. Coincidentally, I was going to that shop so I told them about it right when I pulled in. At least that time, I'm pretty sure it should have been warm enough.  It's always been up there that I've gotten help adjustin them. Sometimes right when I get there, sometimes after it's sat a bit.   It's been frustrating because it comes and goes so hard to say when or if the carb adjustment made any difference.

I put a couple of drops of oil on the weights in the can.  I can't say I knew exactly what I was looking for but the springs looked ok.  Not stretched or anything obvious and I couldn't get them to bind up messing with them by hand.

After tomorrow I'll have some new ignition parts and then will get it timed and have the carbs adjusted again.  Narrowing things down.......hopefully.
  

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Re: That good old hanging rpm topic again
Reply #5 - 08/29/17 at 21:16:57
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IMHO BPT, you should set the timing and do the carb set up yourself first.  Hire or buy a timing light, they aren't expensive and even cheaper to hire.  You'll learn a lot of useful knowledge, as these two steps are crucial elements of tuning your bike.
  

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Re: That good old hanging rpm topic again
Reply #6 - 08/29/17 at 21:59:29
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I am trying to solve a similar kind of mystery with my 78 R100 - but it (for better or worse) has a DYNA III electronic ignition kit on it, so some of the usual suspects are substituted with other suspects.

I do find that I can get my R65 very nicely idling and returning properly to idle with its stock bean can and ignition module setup, but generally do have to get the bike REALLY quite warm , e.g. 30-40km ride first.  Otherwise, I *think* it is adjusted right and stable, and then later find out after longer rides, the idle is around 1500 RPM instead of 1100.

You seem to be methodically checking all the right boxes, though.
  

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Re: That good old hanging rpm topic again
Reply #7 - 08/29/17 at 22:00:35
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tunnelrider wrote on 08/29/17 at 21:16:57:
IMHO BPT, you should set the timing and do the carb set up yourself first.  Hire or buy a timing light, they aren't expensive and even cheaper to hire.  You'll learn a lot of useful knowledge, as these two steps are crucial elements of tuning your bike.


I second this  Wink
  

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Re: That good old hanging rpm topic again
Reply #8 - 08/30/17 at 00:09:35
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Absolutely agree. I don't have a timing light anymore and when I told the guys at the shop they told me to bring it up there. My intention was to have them show me how.  I figured I wouldn't turn down their offer, especially since I have multiple things going on.

Right now I'm completely down. I'll be getting it rideable then hoping they can show me how to get it to the finely tuned point.

Yep, I do need to get a timing light....
  

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Re: That good old hanging rpm topic again
Reply #9 - 08/30/17 at 04:59:41
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nhmaf wrote on 08/29/17 at 21:59:29:
I am trying to solve a similar kind of mystery with my 78 R100 - but it (for better or worse) has a DYNA III electronic ignition kit on it, so some of the usual suspects are substituted with other suspects.

I do find that I can get my R65 very nicely idling and returning properly to idle with its stock bean can and ignition module setup, but generally do have to get the bike REALLY quite warm , e.g. 30-40km ride first.  Otherwise, I *think* it is adjusted right and stable, and then later find out after longer rides, the idle is around 1500 RPM instead of 1100.

You seem to be methodically checking all the right boxes, though.


Thanks nhmaf that's what I was wanting, some other opinions about similar stuff.  I'm not sure how the Dyna III ingnition set up looks sorry, does it have a similar bean can ATU? But good to hear your R65 set up behaves well stock standard.  How many km has your R65 done?

A bit of an update, with the day off I went for a 70km mixed hilly, twisty and flat open road ride just after starting this post (good for running in new piston rings!).  Had a pie halfway so two 35km runs. Before I left I squirted more lube in the bean can through the oval inspection hole on the top.  Cruising at 4000rpm, throttle off and clutch in my problem of slowly falling revs was basically halved, not time wise but a rapid drop of rpm from 4000 until about 2200, where it seemed to hang up and stay for quite a while then continue down to idle, took just as long to get to idle as before tho, if not longer.  Idle speed when stopped is smooth and steady, didn't have to adjust the carbs.
Will give it another squirt before my next ride.
  

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Re: That good old hanging rpm topic again
Reply #10 - 08/30/17 at 06:52:05
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Mrclubike wrote on 08/29/17 at 22:00:35:
tunnelrider wrote on 08/29/17 at 21:16:57:
IMHO BPT, you should set the timing and do the carb set up yourself first.  Hire or buy a timing light, they aren't expensive and even cheaper to hire.  You'll learn a lot of useful knowledge, as these two steps are crucial elements of tuning your bike.


I second this  Wink


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Re: That good old hanging rpm topic again
Reply #11 - 08/30/17 at 22:10:31
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Quote:
Thanks nhmaf that's what I was wanting, some other opinions about similar stuff.  I'm not sure how the Dyna III ingnition set up looks sorry, does it have a similar bean can ATU? But good to hear your R65 set up behaves well stock standard.  How many km has your R65 done?


The DYNA III was advertised as the bee's knees back in the day, but they can have their own sets of issues.  Our venerable airhead specialist, "SNOWBUM" a.k.a Bob Fleischer considers that they can be inconsistent/unstable.   I may try to revert back to the old points setup, but this is what the ol girl came with and I'm trying to get it as right as it can be before giving up.

My 1982 R65LS spent at least 15 years in a damp storage shed which took alot to recover from, but it had less than 13,000 miles on it when I got it.  It is now up to about 28,000 miles and running great.   The longest trip I have taken on it thus far has been about 2400 miles (round trip) from NH down through to Tennessee and thereabouts, and back home.   I've done a couple 600 mile days on it, but the stock seat left me kinda stiff afterward.
  

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Re: That good old hanging rpm topic again
Reply #12 - 08/31/17 at 00:34:16
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nhmaf wrote on 08/30/17 at 22:10:31:
It is now up to about 28,000 miles and running great.   The longest trip I have taken on it thus far has been about 2400 miles (round trip) from NH down through to Tennessee and thereabouts, and back home.   I've done a couple 600 mile days on it, but the stock seat left me kinda stiff afterward.


Far out, she's a spring chicken nhmaf!  Those are some good long trips on her, the most I've done in one round trip is about 1500miles, 2500km, a couple of times and ridden 350 mi (550km) in a day a couple of times.  Many times I've stretched my legs out and ridden with them resting on the crash bars, what a relief!
  

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Re: That good old hanging rpm topic again
Reply #13 - 08/31/17 at 04:17:32
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Hello !
As you have sorted the bean can and ascertained it was not seized,I would add that the carburetor are the problem.
The combination of idle stop position and idle mixture screw make the engine too much fed to return to idle correctly.
I suggest you run the bike until hot, return the idle screws to the factory setting and do an idle synch and set up. When done, adjust the idle screw mixture a very tiny bit to have a smooth idle.
I bet that the problem will disappear but when cold the idle will be too slow and the bike will stall. You will have to run the bike for a few hundred meters for the engine to get to proper temperature. Not a big deal Wink
Last but not least, if you are new to engine tune-up you can learn a bit with the Colortune plug (it ias a transparent plug which allows you to SEE if you have set the idle screw correctly... Sort of a gadget but will help you to relate the combustion in the cylinder to the noise the engine makes and the way the idle screw works.
  
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Re: That good old hanging rpm topic again
Reply #14 - 08/31/17 at 04:41:55
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georgesgiralt wrote on 08/31/17 at 04:17:32:
As you have sorted the bean can and ascertained it was not seized,I would add that the carburetor are the problem.
The combination of idle stop position and idle mixture screw make the engine too much fed to return to idle correctly.
I suggest you run the bike until hot, return the idle screws to the factory setting and do an idle synch and set up. When done, adjust the idle screw mixture a very tiny bit to have a smooth idle.


Hi George, thanks for the info.  What you describe is how I have set up the carbs usually for a while now but it has been giving this hanging rpm.  In the past I've kept to the initial idle mix setting of approx 3/4 turn or a couple of clicks further out.  Then adjusted the stop screws.  This gives me the slowly falling rpm. Another popular method goes, which I'm trying now, by adjusting the mix screws to obtain highest rpm then adjusting the revs down using the throttle stop screws.  I should really bite the bullet and get a plug shorting set up as I think Mrclubike described this week and do it that way.  However I'm still suspecting the bean can springs also, they've probably done 185K km over 32 years now.  I could also try going leaner than 3/4 turn of the idle mix screw, which would be along the lines of what you're suggesting.  I've done that before too, but a couple of years ago now.  Gave good fuel economy but compromised open road speeds. 
Thanks George for reminding I can always go back and start again!  As far as I can remember, the initial setting for the throttle stop screws is one full turn from contact?
  

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Re: That good old hanging rpm topic again
Reply #15 - 09/01/17 at 12:07:57
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Funny, I just bought "Classic Bike", the Britain magazine and they explain how to cure a bad return to tick over for Amal carbs. On the adjacent page there is a picture of the Colortune plug !
as per the factory base settings, I can't tell because I'm 1200 km away from home and have no access to the factory manual. Sorry. But one full turn seem OK to start the bike.
  
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Re: That good old hanging rpm topic again
Reply #16 - 09/01/17 at 14:41:43
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Me being shown as an ex member was only a system glitch which has been sorted but thanks for the kind words at the beginning of this thread which made me blush.


Carb related idle speed hang up can be due to the butterflys being too far open at idle to the extent that the transfer ports are brought into play and continue to flow a mixture of air and fuel. 

The two tiny transfer or transition ports are intended to flow mixture just off idle to smooth the transition onto the needle jet. They should only function when sufficient vacuum is created as the edge of the butterfly passes over them.

In order to make sure the transition ports are not brought into play at idle it's important to achieve the desired idle speed with the minimum possible throttle opening which is effectively the same as saying that the mixture screws are set for maximum idle speed. If the mixture is wrong and the throttle stops are used to compensate by raising the idle speed then this problem can occur.  If the advance mechanism has been eliminated as the source of the problem, a simple test is to temporarily lower the idle speed below normal using the throttle stops. If the problem goes away you know it's carb related and the idle setup needs retuning.

  

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Re: That good old hanging rpm topic again
Reply #17 - 09/01/17 at 21:02:04
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On a hanging high idle a test that's always worked for me is hold the brake, let out clutch to bog the engine down, and then pull clutch back in.  Most often, if it's a sticking advance weight, this will cause the idle do drop back down to where it was originally set.  This is predicated, however, on the idle being properly set in the first place.
  

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Re: That good old hanging rpm topic again
Reply #18 - 09/02/17 at 01:28:39
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Barry wrote on 09/01/17 at 14:41:43:
In order to make sure the transition ports are not brought into play at idle it's important to achieve the desired idle speed with the minimum possible throttle opening which is effectively the same as saying that the mixture screws are set for maximum idle speed. If the mixture is wrong and the throttle stops are used to compensate by raising the idle speed then this problem can occur.  If the advance mechanism has been eliminated as the source of the problem, a simple test is to temporarily lower the idle speed below normal using the throttle stops. If the problem goes away you know it's carb related and the idle setup needs retuning.


Aw Barry, I'm glad you haven't escaped!  As they say, once institutionalised, they can't survive on the outside. He he.  And.. once institutionalised, they learn a lot more..  Good to have some theory behind the symptoms, thanks.  Good news is I bought a couple of wire spokes today to set up the plug shorting technique for adjusting idle mix to get max rpm on each cylinder.  This'll be fun! Won't do it tho until the weather gets ride-able (atrocious at the mo, tho not as bad as Texas, hopoe you guys are OK.. Monte, are you out there too), borrow a great cooling fan from work to set up in front of the bike in the garage and go for a long ride first.  I'm still not 100% the ATU has been discounted but will be able to get a better handle on that by doing this too.

Justin B. wrote on 09/01/17 at 21:02:04:
On a hanging high idle a test that's always worked for me is hold the brake, let out clutch to bog the engine down, and then pull clutch back in.  Most often, if it's a sticking advance weight, this will cause the idle do drop back down to where it was originally set.  This is predicated, however, on the idle being properly set in the first place.


Yes Justin I've found dragging the clutch in gear has always reigned in the hanging idle and it doesn't go back up, which is why I'm still open to the idea the ATU may be the problem.  But as you say, set up the idle correctly first.
  

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Re: That good old hanging rpm topic again
Reply #19 - 09/02/17 at 02:31:52
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Barry wrote on 09/01/17 at 14:41:43:
a simple test is to temporarily lower the idle speed below normal using the throttle stops. If the problem goes away you know it's carb related and the idle setup needs retuning.


Yeah I have kinda done that before and the hanging idle problem hasn't exactly disappeared but is less noticeable.  But it makes it a pig of a thing to ride cold around town stopping at lights etc.  So it will be interesting to see what happens with the improved carb syncing method.
  

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Re: That good old hanging rpm topic again
Reply #20 - 09/03/17 at 03:56:36
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(Photos below...)  Is this a suitable plug shorting technique?  I haven't tried it out in practice yet.  Is simply laying the screwdriver over the spoke enough to short the plug well?  Or does it have to wedged/held pretty tightly down?  The jumper lead in the last photo has a much better result on the ohmmeter as far as resistance goes, (laying screwdriver over spoke and in between cylinder fins gave a variable reading and quite high resistance) but I don't know how successfully I'll be able to attach the jumper wire with the bike running, it has insulated alligator clips but the voltage pulses may be able to come through.  I could always turn the bike off in between doing each side I suppose.
P.S. Keen observers will see a couple of broken cooling fins on one of the heads - that wasn't me!  Smiley
  

L_short_1.JPG ( 123 KB | 3 Downloads )
L_short_1.JPG
L_short_2.JPG ( 146 KB | 3 Downloads )
L_short_2.JPG
R_short.JPG ( 109 KB | 3 Downloads )
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Re: That good old hanging rpm topic again
Reply #21 - 09/03/17 at 06:30:51
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As long as the connections to the spark plug are secure it's fine. Using a screw driver to short to the cylinder head will allow you to move from one side to the other with the engine running. That's pretty much how I do it.
  

Barry Cheshire, England 79 R45
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Re: That good old hanging rpm topic again
Reply #22 - 09/03/17 at 12:17:51
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Are you sure it is safe to use the shorting method on post 1981 bikes (with electronic ignition) ?
I seem to remember it could kill the ICU  ?
But I'm not so sure...
  
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Re: That good old hanging rpm topic again
Reply #23 - 09/03/17 at 14:23:57
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It's safe as long as the HT never goes open circuit which would allow the coils to generate excessively high voltage and possibly break down the insulation.  That why it's important that any temporary HT connections made to facilitate shorting are properly secured.  The temporary act of shorting the HT to earth with a screw driver is not harmful. 

The objective of the shorting method is to stop the spark on one cylinder. The risky way of stopping the spark that really will damage electronic ignition is the old fashioned method of pulling off the HT lead.

Edit:

If we think bout it the HT is strictly speaking not been shorted directly to earth.  It's being connected to earth via the 5K resistor in the plug cap just as it is in normal operation which limits the current.  I wouldn't advise any method of shorting where the plug cap and resistor are taken out of circuit or where a resistor spark plug and non resistor plug cap have been adopted.

   
  

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Re: That good old hanging rpm topic again
Reply #24 - 09/03/17 at 15:07:30
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Going completely off on a tangent, nearly 50 years ago I learnt something of shorting HT literally first hand.

At the factory where I worked it was the custom at Christmas time for all Engineering Apprentices to tour the various trade workshops singing carols in exchange for a money.  At the electricians shop we were also put to the infamous megger test.  Basically you were asked to grab the test leads and receive a shock.  If you timidly held the test leads lightly the shock was quite severe but if you grabbed them firmly like a man the shock was insignificant.  The Electricians knew what they were doing.  A megger is not dissimilar to an ignition coil in that it generates a very high voltage but with very little current which is another way of saying it is a high impedance source. Just as with an ignition coil if you operate a megger nearly open circuit a very high voltage is generated which can give a nasty shock where as if you operate it nearer to short circuit the voltage collapses due to the relative mismatch in impedances of source and load. 

It was a subtle lesson in ohms law never forgotten. I doubt health and safety would permit such a hands on method of learning these days.
  

Barry Cheshire, England 79 R45
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Re: That good old hanging rpm topic again
Reply #25 - 09/04/17 at 01:47:05
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Barry wrote on 09/03/17 at 06:30:51:
As long as the connections to the spark plug are secure it's fine. Using a screw driver to short to the cylinder head will allow you to move from one side to the other with the engine running. That's pretty much how I do it.


Thanks for the affirmation Barry, I pushed a crimp eye terminal over the the spoke and soldered it to the spoke for the spark plug connection, it's solid enough I think. And thanks misterpepper for describing the set up, in another post Wink I'll prob have some time to go for a ride and use it later in the week.
Cheers.
  

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Re: That good old hanging rpm topic again
Reply #26 - 09/04/17 at 18:49:15
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Shorting one lead is the same as a single outlet coil which has one end earthed.
  
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Re: That good old hanging rpm topic again
Reply #27 - 09/04/17 at 21:06:32
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Electric fence is the same, grab it hard and it's not too bad, be a bit timid and a spark  jumps to your hand with a crack...and it hurts. Old engines in equipment used to have a blade bolted to the head, which you pressed against the live sparkplug terminal to shut it down...it didn't pay to think about what you were doing.

Engines have been missfiring for a 100 years, either by the spark shorting to earth or open circuiting - it's not total death of a coil just by going open circuit a few times.  I've seen car engines with the same ignition system as Airheads with a cyl miss firing open circuit for days at a time...and the coils are just fine.
  
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Re: That good old hanging rpm topic again
Reply #28 - 09/05/17 at 10:17:26
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Motu wrote on 09/04/17 at 21:06:32:
Old engines in equipment used to have a blade bolted to the head, which you pressed against the live sparkplug terminal to shut it down


Man, I haven't seen one of those in years!
  

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Re: That good old hanging rpm topic again
Reply #29 - 09/09/17 at 22:31:42
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My mower still has a spark- ground kill switch, broken off the bracket so it's manual push together!

Anyway, doing the plug shorting for syncing the carbs is an easy way of getting the idle mix right, but I was already in the right ball park.  So it hasn't improved the slow drop to idle.  Basically, no matter how I tune the bike, the only way I can set the idle speed at 1000+ rpm is by using the throttle stop screws and I will get the slow return to idle from 3000+ rpm, approx 3-4 secs from 3000rpm.

If I set the idle speed below 1000 rpm, say 600-700 rpm, the idle speed will return far more quickly from 3000+rpm. Obviously this is no good for everyday riding though..

What should I expect as a time for revs to return to idle from 3000 rpm, in neutral, stopped with a hot engine?  Am I just expecting too much for it to return to idle quickly?

If not, I think I may have to do a carb overhaul as well (eh BPT), before pulling the ATU apart.
  

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Re: That good old hanging rpm topic again
Reply #30 - 09/10/17 at 02:37:54
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Woops I should've read Snowbums notes on carb syncing first, looks like you don't set the idle mix by the shorting method, but adjust the idle speed first. Make it quick between shorting sides, 3 secs initially, then shorter.  I'll have to revisit it.  First time I did that I did both sides fairly individually, 30 secs to a min each side.

How fast should I expect a return to idle from 3K rpm, hot engine, please?  Would be a good reference point.
  

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Re: That good old hanging rpm topic again
Reply #31 - 09/10/17 at 03:06:44
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It should return quickly to idle and you are not expecting too much that it does. I'm going for a ride this morning so I'll note how long it takes but I'd guess 1 or 2 secs at most.
  

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Re: That good old hanging rpm topic again
Reply #32 - 09/10/17 at 06:02:16
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After 20 odd miles mine dropped to idle in 2 seconds.
  

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Re: That good old hanging rpm topic again
Reply #33 - 09/10/17 at 15:53:51
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I'll have to pay attention but I think all of ours return to normal idle immediately after a "normal" high speed circuit.
  

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Re: That good old hanging rpm topic again
Reply #34 - 09/12/17 at 00:28:12
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OK thanks Barry and Justin for the info on what I should be getting for a return to idle.  Rather than do another carb sync session I'm going to overhaul the carbs first, I (embarrassingly) remembered last night, from a thread a couple of years ago, that I bought the bike with an R80 carb on the left side and I have all the gaskets, OEM diaphragms, needles, new main and idle jets and new venturi to make them the same.  Better do this first I think  Grin  I'll post again with the results.
  

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Re: That good old hanging rpm topic again
Reply #35 - 09/17/17 at 02:56:24
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Overhauling the carbs has not given me a quick fix to the slow return to idle, it's just the same.  Granted I still need to spend some time syncing the carbs again, but after a 40min run with a few stops to give a basic set up, the revs are still taking a long time to return to idle, still approx 4-5secs from 4000 rpm.

So if I can't fix the slow idle return by syncing the freshly overhauled carbs I guess I'll be looking at the bean can.  But there's one thing that confuses me if this is the problem - how can a couple of small weights hold up the revs?  I don't believe the inertia of them would over power the friction and compression of the cam and crankshaft.  So would the bean can cause hanging idle because the firing, if it's advanced, causes the engine to speed up?

Or could my problem of slow return to idle be caused by poor compression?  'Cause I have to admit I was pretty surprised to have only 100 psi each side, with new rings and a fairly new head recondition. Hmmm...
  

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Re: That good old hanging rpm topic again
Reply #36 - 09/17/17 at 03:32:02
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tunnelrider wrote on 09/17/17 at 02:56:24:
how can a couple of small weights hold up the revs? 


If the bean can is at fault then the obvious part of the answer is the weights are sticking and allowing too much ignition advance.

The more subtle part of the answer requires an understanding of the impact of ignition advance on idle revs.  Ignition timing at idle is 6 Deg before TDC  and at full advance 32 Deg before TDC.

The key to the phenomena is to realise that 6 deg BTDC at idle is a compromise between easy starting and and a smooth idle. The most efficient amount of ignition advance at idle in terms of the power produced when there is no load on the engine is quite a lot more more than 6 Deg BTDC. What this means in practice is if you apply more ignition advance at idle the revs will rise without touching the throttle. 

So if the centrifugal advance mechanism is not doing it's job and allowing too much advance as the revs fall then the engine is going to either hang up at higher revs or the revs will fall slowly.




The impact of ignition advance on idle speed was utilised by some electronic ignition manufacturers to provide an idle speed stabilisation effect.
If you look at this graph the amount of ignition advance actually increases if the revs for some reason fall below the desired idle speed range. This will tend to stabilise the idle speed by producing a little more power to push the revs back up again. Note that the advance curve is flat between 900 RPM and 1100 RPM which would be the normal range of idle speed settings. If the idle speed was set above 1100 RPM then there would be a potential for idle hang up.


  

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Re: That good old hanging rpm topic again
Reply #37 - 09/17/17 at 03:46:42
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Barry wrote on 09/17/17 at 03:32:02:
The more subtle part of the answer requires an understanding of the impact of ignition advance on idle revs.  Ignition timing at idle is 6 Deg before TDC  and at full advance 32 Deg before TDC.

The key to the phenomena is to realise that 6 deg BTDC at idle is a compromise between easy starting and and a smooth idle. The most efficient amount of ignition advance at idle in terms of the power produced when there is no load on the engine is quite a lot more more than 6 Deg BTDC. What this means in practice is if you apply more ignition advance at idle the revs will rise without touching the throttle.

So if the centrifugal advance mechanism is not doing it's job and allowing too much advance as the revs fall then then the engine is going to either hang up at higher revs or the revs will fall slowly
                   


Thanks Barry for your concise explanation of the subtleties of idle and ignition advance. Yes I've suspected this.  I read on an old thread I found by searching the topic, posted by an ex member 'airhead' that he reconditions bean cans and is finding that a lot are coming in, suggesting they have found their service life.  This was a post from 2008!

At least my carbs are clean! Smiley
  

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Re: That good old hanging rpm topic again
Reply #38 - 09/17/17 at 04:23:00
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Barry wrote on 09/17/17 at 03:32:02:
The impact of ignition advance on idle speed was utilised by some electronic ignition manufacturers to provide an idle speed stabilisation effect.
If you look at this graph the amount of ignition advance actually increases if the revs for some reason fall below the desired idle speed range. This will tend to stabilise the idle speed by producing a little more power to push the revs back up again. Note that the advance curve is flat between 900 RPM and 1100 RPM which would be the normal range of idle speed settings. If the idle speed was set above 1100 RPM then there would be a potential for idle hang up.


Yeah that's interesting and the graph, thanks for finding that.  Is the electronic tachometer (rev counter) usually pretty accurate in high km BMW's?

I think I can borrow an external tacho, and test if it's still accurate.  If I recall correctly it works by counting a spinning mark when aimed at it, like a timing light.  Only problem is that I've got three marks on the flywheel (clutch carrier thing) that are painted.  Have you or anyone out there done this and can give me a couple of tips?  I know this won't fix the problem though but I've been a bit curious to how accurate it is 5K+ rpm.  It got knocked once and the upper revs dropped 500rpm on the tacho for a while, has since returned to how it was.
  

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Re: That good old hanging rpm topic again
Reply #39 - 09/17/17 at 08:54:58
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I've not tested a tachometer but it should be reasonably accurate certainly more so than a speedo.   

On the basis of observing road side radar speed readings, if I had to guess I'd say mine is modestly optimistic, perhaps over reading by 2 or 3%.  It will be interesting to see what you find.  How about a spot on the end of the alternator rotor or is the diameter too small for that to work.

  

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Re: That good old hanging rpm topic again
Reply #40 - 09/17/17 at 10:38:18
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It could be easy to test a tacho if you have a small power outlet giving you 12 V in alternating current. (no so widespread because they are often used to charge batteries, hence direct current).
Your alternating current is say 50 periods per seconds. So it is 50x60 periods per minutes. So 3000 periods per minutes. If your tacho react on negative signal the tacho should read1500 RPM...
If on 60 Hz mains, make the math yourself Wink
My tacho was suspected to be reading low. So I opened it and renewed the capacitors in it and it returned to a more plausible reading... 35 years of life in a device exposed to hot, cold humid or excessively dry atmosphere is a harsh environment...
  
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Re: That good old hanging rpm topic again
Reply #41 - 09/17/17 at 10:54:40
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If you are going to take your bean can completely apart
Make sure you get some new advance springs
they are cheap and you will more than likely  over stretch the old ones getting it apart

But you can just knock the pin out of the drive and pull the guts out and not dissemble any further
clean it up with some electronic parts spray
And then lube the advance mechanism and bushing with some light oil
Put it back together
It still would not hurt to replace the springs

You also need  to check and see what your   advance is
It should be 26 deg (6 minus 32 equals 26)
If it is more than that you should bend the stops in just slightly so it doesn't over advance   and cause spark knock
  

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Re: That good old hanging rpm topic again
Reply #42 - 09/17/17 at 22:28:02
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The last one I did had the weights rusted and I had to soak it in penetrating oil for a while...
  

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Re: That good old hanging rpm topic again
Reply #43 - 09/18/17 at 23:48:57
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Mrclubike wrote on 09/17/17 at 10:54:40:
It still would not hurt to replace the springs

You also need  to check and see what your   advance is
It should be 26 deg (6 minus 32 equals 26)
If it is more than that you should bend the stops in just slightly so it doesn't over advance   and cause spark knock


Thanks Mrclubike yeah I'm just about to order new springs.  I presume checking your advance involves looking at where the advance line is in relation to the centre of the timing hole, once timing has been set at idle?  If so mine is ok.  I remember reading about this in one of Snowbum's fantastically involved pages, which I'll probably trawl through again once the springs turn up and I do the 'bean can job' but my advance was in the centre, as it was at idle.  I'm going to use this link as a guide for dissembling, which should be enough info.
http://gunsmoke.com/motorcycling/r100gs/auto_advance/index.html
Once again, I'll post with the results!  It takes about 10 days for Motobins parts to arrive here.
Thanks all you've been great with your information.
  

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Re: That good old hanging rpm topic again
Reply #44 - 10/09/17 at 01:25:42
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I had time today to pull apart the bean can.  The springs were obviously stretched compared to the new ones (see the photo below comparing a new spring and the old one). Apart from replacing these all I did was take off the weight arms and lube the pivots. I also lubed the main shaft that the Hall sensor rides on. All back together successfully but unfortunately didn't go for a test ride due to the weather!  I set the timing and noticed full advance is not achieved until now 4000rpm, which seems a bit high to me (it was about 3000rpm before).
  

ATU_springs.JPG ( 43 KB | 3 Downloads )
ATU_springs.JPG

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Re: That good old hanging rpm topic again
Reply #45 - 10/09/17 at 06:18:54
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Hard to know what to do with the new springs. A delayed maximum advance is not best for power but if it cures the problem. Maybe they'll improve with age. 

Was there any slack in the way the old springs fitted ?
  

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Re: That good old hanging rpm topic again
Reply #46 - 10/09/17 at 06:43:01
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tunnelrider wrote on 10/09/17 at 01:25:42:
full advance is not achieved until now 4000rpm,


In your previous post you stated that your advance was spot on.
" once timing has been set at idle?  If so mine is ok"

If the original springs were doing their job they should look like the new springs just older (if springs gain patina with age).

If the old springs performed as they should and now you have installed new springs that physically look different and the advance is bonkers, MY BET is that they have sent you the wrong springs.

I'm not much as a mechanic, but I can hold my own with wagers Cool


  

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Re: That good old hanging rpm topic again
Reply #47 - 10/09/17 at 08:08:51
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The new springs are obviously stronger so the bob weights can't raise sufficient centrifugal force to extend them to the stops until 4000 RPM.

So how much are the springs too strong ? 

Well it's not 1000RPM/3000RPM or 33%.  The relationship between RPM and centrifugal force (or centripetal force if anyone wants to be pedantic) has a square function in it so the spring is more like twice as strong as it should be.

Wilcom could be right, they sent the wrong springs.
  

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Re: That good old hanging rpm topic again
Reply #48 - 10/09/17 at 10:09:03
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Errrr, Barry,
My guide says that the maximal advance is at 3500 RPM So a little less than the 4k observed...
  
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Re: That good old hanging rpm topic again
Reply #49 - 10/09/17 at 12:14:23
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My riders handbook and BMW workshop manual both say maximum advance is at 3000 RPM. 

Perhaps it changed to 3500 RPM for the electronic ignition models.  If it did then ideally there should be two spring rates available.  Motobins only supply one type of spring which would be a compromise even if accurate.   Which brings us to the point that there are no genuine BMW spares for the bean cans. Any springs available are after market parts which may not have been accurately reproduced.  To check I would measure the old and new springs. The spring wire diameter, number of coils and overall spring diameter should be the same. If they are then they both have the same spring rate and it can only be the overall length that is causing the problem.
  

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Re: That good old hanging rpm topic again
Reply #50 - 10/09/17 at 19:46:21
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Take it back apart and give the spring anchor post a little bend in towards the center

I replaced mine with the springs Moto bins sells and they are working fine after I gave them a little tweak
  

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Re: That good old hanging rpm topic again
Reply #51 - 10/09/17 at 20:27:20
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I must have missed something but why were they changed if the timing advance was spot on?
  

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Re: That good old hanging rpm topic again
Reply #52 - 10/09/17 at 22:06:37
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Justin B. wrote on 10/09/17 at 20:27:20:
I must have missed something but why were they changed if the timing advance was spot on?
                   

Because the revs took a long time to return to idle once the engine is hot.  Cold yes the timing advance works fine.  Sorry I've not had the chance to reply to any of your good replies yet. My rider's handbook that is the bike's original book says full timing advance at 3000rpm, so yes, apart from the slow drop in revs once hot it was working as it should.  But it was not working as it should when at normal operating temp.
Probably not much use, but for the experience, plus the fact I haven't test ridden it with the new springs put on 'straight off the shelf' I'm just about to take it for a test ride. I expect there will be a hit in low end performance.

Mrclubike wrote on 10/09/17 at 19:46:21:
Take it back apart and give the spring anchor post a little bend in towards the center


Aww taking that thing apart and putting back together is about as enjoyable as going to the dentist!
  

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Re: That good old hanging rpm topic again
Reply #53 - 10/09/17 at 22:24:14
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In my experience the slow return is crud/rust causing the weights to be sluggish/sticky.
  

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Re: That good old hanging rpm topic again
Reply #54 - 10/10/17 at 02:20:27
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So a good hilly test run proved the new bean can springs are too tight, the bike was pretty sluggish increasing revs from 2000rpm especially in 4th/5th under load.  There's not a massive difference but my bike needs all the performance it can get.  On the plus side, the revs do drop back to idle properly!

When I got back I checked the timing again, advance with the new springs starts at approx 2000rpm and finishes at just over 4000rpm.  So the bean can will have to come off and entered again.  Firstly though I might try mucking around with the timing and see if I can set full advance at 3000rpm.

Mrclubike wrote on 10/09/17 at 19:46:21:
Take it back apart and give the spring anchor post a little bend in towards the center

I replaced mine with the springs Moto bins sells and they are working fine after I gave them a little tweak

What was your experience with the Motobins springs when you installed them Mrclubike?  Were they too tight as well?  By bending the spring anchor post in towards the center a little I presume you are decreasing the length of the spring.  Do you mean bending the anchor post on the weight arms?  How much did you bend it, about 1mm?  And have you got your advance starting at 1500rpm and finishing at 3000rpm now?

I'm half tempted to put the old ones back on and cover the slower decrease in revs to idle by dropping my idle speed below 800rpm, which pretty much does the trick especially for open road riding.

I don't think they are the wrong springs they sent, I doubt if they sell other springs like these.


  

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Re: That good old hanging rpm topic again
Reply #55 - 10/10/17 at 05:01:53
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After looking at them on the Motobins site I'd agree they have not sent the wrong springs as the other pre-bean can springs they stock are quite different.  It must just be they are after market springs and too short which will cause your problem even if they managed to get the  spring rate correct. Advance not beginning until 2000 RPM is a sure sign they are not right as BMW say advance should start at 1500 RPM.

I'd be inclined to refit the old springs provide there is no slop in the bob weights once fitted. You could check at what RPM advance then begins.  If there is slop because the old springs are too long then you have to aim in the middle either by bending the spring anchors or stretching the new springs.  Stretching springs is tricky to say the least and risks ruining them so bending the anchors may be safer.
  

Barry Cheshire, England 79 R45
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georgesgiralt
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Re: That good old hanging rpm topic again
Reply #56 - 10/10/17 at 05:06:17
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Apologies,
I've just looked at the factory course material for model AFTER 1985.
They say that the maximal advance is achieved "around 3000 RPM" and for a total advance of 32° before TDC.
So maybe your settings are not that bad regarding the 3000 RPM but too slow the slope considering your riding results... Are you sure of the static setting ?
  
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Mrclubike
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Re: That good old hanging rpm topic again
Reply #57 - 10/10/17 at 19:39:04
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I would try bending them about 1 mm

I cant remember exactly what I had when I started
I had them bent out for the old springs so I had to bend them back for the new springs

You will not have to disassemble the shaft just remove it from the housing

I am wondering if it can be gotten to thru the little window if you knock out the cover

Bosch had to tune them some how
  

window.jpg ( 130 KB | 2 Downloads )
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tunnelrider
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Re: That good old hanging rpm topic again
Reply #58 - 10/10/17 at 22:36:03
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Mrclubike wrote on 10/10/17 at 19:39:04:
I am wondering if it can be gotten to thru the little window if you knock out the cover

Bosch had to tune them some how


Now there's a thought Mrclubike. If possible and not too fiddly to do it would sure beat pulling it apart again. What's going on with your extra big window in your photo above by the way?
Barry the old springs did not have any slop.  Unfortunately I did not test the timing advance start and finish rpm when the engine was hot with the old springs, only cold, but I'd say it was still about where it should be when hot.
You could say, based on this, that there was some crud holding the weights up but it was pretty clean in there and the weight pivots were definitely loose enough to not cause any problems.  It is tempting to think that just by opening it up it may've dislodged something that was causing the problem which is possible so I should refit the old springs.
So what to do next.  Firstly I'm still going to try setting full advance to 3000rpm and see what that does.
Presuming that is no good I've got a couple of options - try and work through the window to push the spring anchors inwards a little, probably very fiddly.
Maybe take it apart and put the old springs on again.  Maybe take it apart and push the anchors in a little.  Whatever I do, I don't really want to be going in there again more than once, I've also got a four day bike trip coming up in a week.  I'm going to read Snowbum's thoughts on it all too.
 
  

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Re: That good old hanging rpm topic again
Reply #59 - 10/11/17 at 02:52:52
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Time for some more useless info.  Trying to set max advance at 3000rpm didn't work, as turning the bean can to the stops anti clockwise did put the advance line in the timing hole at 3000rpm but further revs caused it to disappear above the hole.
It does seem like it'd be possible to bend the spring anchors through the inspection window, one way would be to chock one weight arm spring anchor against the end of the hole with a screwdriver or something then turn the driving dog against it.  Not exact science by any means. I didn't attempt it yet.  But my bean can does have some existing marks that suggest this might've been done before but these may be from a previous entry too, before mine.
Since you all appreciate pictures, below are the original springs.  One has stretched approx 1mm more than the other, perhaps giving my original problem of slow return to idle when hot.  Or maybe a PO had stretched them, who knows really.
  

original_springs_1.jpg ( 77 KB | 1 Download )
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original_springs_2.JPG ( 139 KB | 2 Downloads )
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 1985 Black R65  -  2001 DRZ400 dirt only
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Re: That good old hanging rpm topic again
Reply #60 - 10/11/17 at 03:46:50
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Hello !
I was upset to read that the max advance should be obtained at 300 RPM as my memory was saying 3500 RPM.
So I dig further.
The owner booklet for my R65 (1982) says 3500. The factory manual says "above 3000". And a French Clymer equivalent says 3500 ....
So I bet there has been variations for the actual value or that BMW has changed it's mind over the years... 
Go figure...
  
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Re: That good old hanging rpm topic again
Reply #61 - 10/11/17 at 18:07:49
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tunnelrider wrote on 10/10/17 at 22:36:03:
[quote author=Mrclubike link=1504037694/57#57 date=1507682344] What's going on with your extra big window in your photo above by the way?


It is to fit the hall effect sensor bracket that I made
So it is easier to change on the road
You now know what a pain that thing is to take apart 
  

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mounted_bean_can_001.JPG ( 150 KB | 1 Download )
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Re: That good old hanging rpm topic again
Reply #62 - 10/15/17 at 04:21:24
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Hey Mrclubike that's pretty clever, well done on your fabrication!  I reckon if you use your bike as an adventure bike it's a fantastic idea, after going into the bean can I was thinking how susceptible they might be to a stream crossing in high flow, which I've done before with no problems (touch something wood here!)
I'm hoping that mine never goes 'kaput' on the road...  But was pretty nervous whether the whole thing would work again after a couple of rounds taking it off and messing around with it.
I've ended up putting the old springs back on, feel the bike is a bit more sprightly with them on and haven't got the original problem anymore either. Still would like the revs to come down a bit faster than now but better than before. I straightened up my spring anchors, I think they may've bent in perhaps with age and amount of km's (it's sitting on 186 000 km), also possible the springs have been replaced before and stretched since. With the straightened spring anchors the old springs are more stretched at rest now than they were.  Advance starts a little later, at approx 1700rpm and still stops at 3000 with the springs being stretched a bit further at rest.  I'm OK with it.

I think I bent the spring anchors down so far for the new springs (through the inspection window) that the springs were rubbing on the weight arms which caused further friction but with five days to go before a trip I'm not messing around with the new springs any further at the mo.

Second time around and with better punches it was much easier to get apart and rebuild the bean can, so I'd give it a novice pain in the a... 7/10 rating for risky work!
Oh and it is possible to bend those outer spring anchors through the inspection hole, nice idea Mrclubike.  Cheers.
« Last Edit: 10/15/17 at 06:15:20 by tunnelrider »  

 1985 Black R65  -  2001 DRZ400 dirt only
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