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svejkovat
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Damn. Still dealing with high idle
08/25/18 at 20:43:29
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Does my '83 R65 have an a mechanical advance under the beancan?

I've rebuilt the carbs and was sure that the problem had vanished.  I'd even put a few mid range trips in with no problem.   Yesterday I took the highway about 20mi out of town and when I reached the next city the idle would not return below 3000.  I can jog it down by bumping the clutch.

It will behave, it seems, all day long in city traffic.   10 minutes at 5500 rpm and when I stop for the next light it idles at 3000.   Takes a while to return to 1200 and is irritating to ride since it essentially has no downshifting brake and changes the feel of riding. 

Mechanical advance?   Lube the mechanism?  Replace the springs?   No mechanical advance on my bike?  What to check next then?
  
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Mrclubike
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Re: Damn. Still dealing with high idle
Reply #1 - 08/25/18 at 22:06:40
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The mechanical advance is in the lower half  of the Bean Can

I don't think a sticking advance can cause a 3000 rpm idle
Easy enough to check the timing with a timing light

I would look at a sticking throttle plate in the carb
Did you replace the O rings on the throttle shafts
  

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Barry
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Re: Damn. Still dealing with high idle
Reply #2 - 08/26/18 at 04:35:00
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What hot idle speed do you have the carbs set at ?

If above 1000 RPM do a simple experiment:

Lower the idle speed by backing off the idle stop screws equally both sides and see if it has an impact on the problem.
« Last Edit: 08/26/18 at 05:59:10 by Barry »  

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svejkovat
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Re: Damn. Still dealing with high idle
Reply #3 - 08/26/18 at 10:29:45
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Haven't been able to look into anything yet today.

I rebuilt the carbs a few hundred miles ago and it's been running like a top.  Very strange then that it's suddenly exhibiting similar to just before the rebuild.

I did not replace the butterfly orings.  The orings elsewhere were in very good shape and the engine is low mileage and has always been well stored.  I replaced all other orings.  I don't think this oring could be a culprit judging by the very conditional nature of the problem. Could do a simple test of this by supergluing an oring outside and snug to the body.

I wonder why, specifically, high idle is a problem only after spending five minutes or more at high rpm.  Can run around town all day long... no problem.  Take it out on the highway for a good fast 10 mile stretch.  Idle sticks at 3000.

What has me especially worried is if this indicates a way too lean condition happening when I'm at speed on the highway for some reason. 

I did find some chafing marks on the steel cylinder of one of the diaphragm carriers during the rebuild. This cylinder is aluminum and the shaft it slides on is stainless steel.  The chafing likely had a little aluminum build up that I honed off with scotchbright. 

I'll go back into the diaphragm carriers/dampers and see if it's reappeared.  If so this would make perfect sense of things.  If I have to reclean/rehone some chafing off again I'll look into adjusting the alignment of that diaphragm.

I may invest in a couple of mikunis some day after all Smiley

I'll report back in any case and thank you for the suggestions.
  
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Mrclubike
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Re: Damn. Still dealing with high idle
Reply #4 - 08/26/18 at 20:09:51
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The problem with the throttle shaft Orings is they  swell and cause the throttle shaft to stick
You have to grind the peened over screw off of the throttle shaft  to remove them and refit new screws during reassembly 
That is why they never get replaced

Remember it takes very little throttle opening in neutral to get a higher idle
  

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Kelvin
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Re: Damn. Still dealing with high idle
Reply #5 - 08/27/18 at 06:30:12
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I'm wondering if one of the carburettor pistons is jamming open. You go out at high (engine) speed for a bit, the piston rises. You close the throttle and one of the pistons jams high. The intake sucks mixture from the idle circuit, but also from the main circuit, that would normally have the main needle blocking flow.

It's unlikely that this would happen in both carburettors simultaneously, so: 1) is it a rough idle, driven by one cylinder? And, 2) if you tap the carburettor body with a small hammer to un-jam the piston, does the problem rectify?

The lazy cylinder has noisier tappets, start by tapping the carb on the quiet side of the engine.
  

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Justin B.
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Re: Damn. Still dealing with high idle
Reply #6 - 08/27/18 at 23:22:11
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If the idle is too high after getting off the freeway, come to a stop, apply brake, then ease out the clutch and bog the engine down.  If the idle returns to normal then it's likely the advance mechanism is sticking. 

Yours are the exact symptoms our '80 had with a sticky advance.
  

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Re: Damn. Still dealing with high idle
Reply #7 - 08/28/18 at 10:08:02
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Check that your chokes are not sticking partially open.

When you experience a high idle, push down on each choke lever to see if it is bottomed out.  If not, that may be your problem.
  
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svejkovat
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Re: Damn. Still dealing with high idle
Reply #8 - 08/28/18 at 11:56:23
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Justin B. wrote on 08/27/18 at 23:22:11:
If the idle is too high after getting off the freeway, come to a stop, apply brake, then ease out the clutch and bog the engine down.  If the idle returns to normal then it's likely the advance mechanism is sticking. 

Yours are the exact symptoms our '80 had with a sticky advance.


Sorry for such ignorance.  I thought I knew my bike better. But it's confirmed then that I have a mechanical advance?

I have yet to take off the 'bean can'.   I've been pretty busy.  I will tonight.  I've read alternately that one or both, sticking fly-weights and/or weak springs, may be the culprit.   

??

I'll go in and check, free things up, lightly lube, and report back.
  
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Re: Damn. Still dealing with high idle
Reply #9 - 08/28/18 at 14:29:24
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In our range of years, the bean can was kind of a hybrid.  It has the electronic Hall sensor but still has the mechanical advance part spinning around in there.  That's where the things can get stuck or the springs stretched.  So maybe that can help with some of your confusion?

It's a pain to get the can completely apart.  You can see (kind of...) the parts talked about here through the little oval hole.  That cap isn't sealed but could be difficult to pop off if it hasn't been for a while (I slide a razor blade under the lip to get it started, the metal is a bit soft).
You have to be careful with lube here.  Some say don't, but guys here have said to use it very sparingly and use the proper stuff.  If you use the wrong kind or too much, it'll fling all over and cause more problems.  Through that little window though, you might be able to see if there is any obvious corrosion or something else causing them to stick.

If you haven't already, search here or Google "bmw beancan disassembly" or something similar and you'll be able to see where all the parts are.
  

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Re: Damn. Still dealing with high idle
Reply #10 - 08/29/18 at 03:14:02
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svejkovat wrote on 08/28/18 at 11:56:23:
I've read alternately that one or both, sticking fly-weights and/or weak springs, may be the culprit. 

??

I'll go in and check, free things up, lightly lube, and report back.


I think you're looking at the right spot, as Justin said with his '80 and I had with mine last year, same symptoms.  Playing around with the fly weight spring tension by pulling up the spring anchor maybe 1mm each spring, increasing the preload of the spring, worked for me.  You can actually do this through the oval inspection hole with the bean can off the bike if you know what you are looking at, would save having to take the bean can apart. Like BPT said, by looking at some pics of a disassembled bean can you can get familiar with the insides.

But reality is I took my bean can apart twice before I was familiar enough to make the right adjustments.  First time I put new springs on but ended up going in again, putting the old ones back on and increasing the preload a little. 8K km later it's still working OK.

Spraying some lube in at the fly weight pivots through the inspection hole should make some difference if sticky weights and/or weak springs are holding up the revs.  I used a liberal amount of CRC556 and light oil initially, then tried chain lube, all which made some difference to dropping the revs.  You can drain the excess by unscrewing the bottom Phillips screw on the outside of the case, on or off the bike. But this never made my high rev problem go away completely, I had to adjust the spring anchor posts.

  

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Justin B.
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Re: Damn. Still dealing with high idle
Reply #11 - 08/29/18 at 19:16:04
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In the case of the '80 they were rusty and nothing in the advance mechanism worked freely.  I had to disassemble, clean, polish pivots, lube, and reassemble.  Not really hard but "fiddly" as our Bros. across the pond might term it.
  

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Re: Damn. Still dealing with high idle
Reply #12 - 09/06/18 at 20:44:03
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Indeed - you may want to do some of the disassembly in a clear plastic bag as there are a couple small parts that like to shoot out and get lost.   Somewhere around here I thought I had some instruction from an internet site (now apparently unreachable) about R&R for these things... will look some more for it...
  

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Re: Damn. Still dealing with high idle
Reply #13 - 09/06/18 at 20:54:39
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In meantime, I've found some merged threads covering this topic from earlier forum discussions - has quite a bit of info and disassembly pics.  I cannot attach it here as it is too big (4MB).  I will see if I can put it on dropbox or something, or else PM me your email address and I can try to email it
  

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