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Very Hot Topic (More than 25 Replies) Main jets? (Read 442 times)
Tony Smith
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Re: Main jets?
Reply #15 - 05/06/18 at 23:46:22
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DadsR65 wrote on 05/06/18 at 18:28:40:
Bob_Roller wrote on 05/06/18 at 14:47:10:
The diaphragms, are they Bing parts, or aftermarket pattern parts ??


Hmmmm...interesting question.† This one took a bit of digging, but here's what I used:

https://www.eubmw.com/collections/carburetor-kits/products/bing-carburetor-kit

I can't tell if it's OEM Bing or not.



And it doesn't matter a damn if they are or are not OEM. providing of course that they are good quality and seal correctly.

The "non-OEM" diaphragm thing started a few years back when some one had difficulties after rebuilding their carbs and assembling them wrong. They tore down and rebuilt, but with OEM diaphragms and wonders of wonders the bike ran correctly - obviously it was the diaphragm's fault.


The myth persists.......


Thing is, if you look at the vacuum system in a Bing carb it is immensely powerful (relatively speaking) a  "stiff" diaphragm (within any rational meaning of the term) can do nothing more than slow the rate of change, it cannot alter the amount the slide will rise because vacuum is vacuum.

I have been using non-OEM diaphragms since 1980, and I have never had a problem. Initially Stromberg diaphragms, but more recently whatever Moto-Bins is flogging as the OEM alternative.

I have miss-assembled carbs on occasions and I have sucked up the fact that I made a mistake and fault diagnosed till I found and eliminated my own mistake.

In no particular order I set out below a list of things that can cause your problem (or similar) for you to check.

Diaphragms seated correctly in both carb body and slide.

Dome seating correctly and no leak at the top (if there is the 'approved" fix is the BMW badge that is the same diameter and epoxy - if you are in the USA you can send the dome to Bing USA for removal of the metal "bung" fittment of a new one and re-crimping, but be aware that the price is pretty much the same as just buying a new dome.

Slides have full, free and correct movement available, all airways (vacuum ways I suppose) not clogged

Start enrichment circuit assembled correctly and all screws tight

Emulsion tubes clean and correctly mounted to jet assembly

Funny looking flat washer fitted to mainjet - you would be amazed how many people remove this and either do not replace it, or replace it with a much smaller one - the odd looking oversized washer is the correct one and does an important job.

Float valve, needle and seat and floats not binding and flowing fuel freely. It is possible to miss-assemble these so that they can "hang up", but usually the lack of fuel in the bowls is a dead giveaway.

Intake trunk rubbers on the cylinder heads in good condition and snug tight to both head and carb

Check plastic intake trumpets and make sure any rags you stuffed in there on disassembly were removed when you put it back together (don't ask me why this one is included).

Airfilter, clean and good quality (which includes not being an oiled fabric piece of rubbish) - sometimes OEM, or a good copy, is best.

If you had the throttle plates out are you absolutely sure they went back in the right way round?

Fuel tap in god condition and flowing correctly? There is a filter built into the tap, it is known to clog.

Fuel lines in good condition and not kinked anywhere? My personal trick was to trap the cross feed pipe on an early model R65 with clam shell aircleaner - it flowed enough to trick me for some time, except that the RHS carb would run dry quite quickly at WOT or thereabouts. I felt a 1st class dill when I eventually found it.

Recheck every jet, a minute piece of lint will change the flow characteristics for the worse.

Once you are absolutely sure that your carbs are OK, start checking ignition components - on the well established principle that if you *think* it is fuel it will be electrical - and vice versa.
  

1978 R100RS| 1984 R65 | 1984 XT350 | 1992 KLE500 | 2002 R1150GSA
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BPT
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Re: Main jets?
Reply #16 - 05/07/18 at 10:24:06
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The EUBMW parts aren't Bing but I've seen good reviews of those and other parts they provide.
  

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wilcom
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Re: Main jets?
Reply #17 - 05/07/18 at 12:02:32
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Tony Smith wrote on 05/06/18 at 23:46:22:
And it doesn't matter a damn if they are or are not OEM.


I just ordered and received kits for my carbs(O-rings, gaskets and diaphragms) for about $20 so I don't think I got the OEM parts.

I felt the diaphragms and my sensitive lil pinkies could not discern ant difference from the ones on the bike now. and as Tony said, the difference in material would have to be huge to make any difference at all,  considering the amount of vacuum power acting on them.
  

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guyom
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Re: Main jets?
Reply #18 - 05/08/18 at 08:41:19
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hahah ! got exactly the same problem for the same job... Smiley does not like the cold.. and lost of power at full open throttle...
  
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DadsR65
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Re: Main jets?
Reply #19 - 05/10/18 at 05:57:15
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Tony Smith wrote on 05/06/18 at 23:46:22:
DadsR65 wrote on 05/06/18 at 18:28:40:
Bob_Roller wrote on 05/06/18 at 14:47:10:
The diaphragms, are they Bing parts, or aftermarket pattern parts ??


Hmmmm...interesting question.† This one took a bit of digging, but here's what I used:

https://www.eubmw.com/collections/carburetor-kits/products/bing-carburetor-kit

I can't tell if it's OEM Bing or not.



And it doesn't matter a damn if they are or are not OEM. providing of course that they are good quality and seal correctly.

The "non-OEM" diaphragm thing started a few years back when some one had difficulties after rebuilding their carbs and assembling them wrong. They tore down and rebuilt, but with OEM diaphragms and wonders of wonders the bike ran correctly - obviously it was the diaphragm's fault.


The myth persists.......


Thing is, if you look at the vacuum system in a Bing carb it is immensely powerful (relatively speaking) a† "stiff" diaphragm (within any rational meaning of the term) can do nothing more than slow the rate of change, it cannot alter the amount the slide will rise because vacuum is vacuum.

I have been using non-OEM diaphragms since 1980, and I have never had a problem. Initially Stromberg diaphragms, but more recently whatever Moto-Bins is flogging as the OEM alternative.

I have miss-assembled carbs on occasions and I have sucked up the fact that I made a mistake and fault diagnosed till I found and eliminated my own mistake.

In no particular order I set out below a list of things that can cause your problem (or similar) for you to check.

Diaphragms seated correctly in both carb body and slide. Verified

Dome seating correctly and no leak at the top (if there is the 'approved" fix is the BMW badge that is the same diameter and epoxy - if you are in the USA you can send the dome to Bing USA for removal of the metal "bung" fittment of a new one and re-crimping, but be aware that the price is pretty much the same as just buying a new dome.Inspected, looks ok

Slides have full, free and correct movement available, all airways (vacuum ways I suppose) not cloggedVerified

Start enrichment circuit assembled correctly and all screws tightVerified

Emulsion tubes clean and correctly mounted to jet assembly Verified

Funny looking flat washer fitted to mainjet - you would be amazed how many people remove this and either do not replace it, or replace it with a much smaller one - the odd looking oversized washer is the correct one and does an important job.Verified

Float valve, needle and seat and floats not binding and flowing fuel freely. It is possible to miss-assemble these so that they can "hang up", but usually the lack of fuel in the bowls is a dead giveaway.Verified

Intake trunk rubbers on the cylinder heads in good condition and snug tight to both head and carbVerified

Check plastic intake trumpets and make sure any rags you stuffed in there on disassembly were removed when you put it back together (don't ask me why this one is included).Verified

Airfilter, clean and good quality (which includes not being an oiled fabric piece of rubbish) - sometimes OEM, or a good copy, is best.200 miles on new filter (not K&N)

If you had the throttle plates out are you absolutely sure they went back in the right way round?Verified

Fuel tap in god condition and flowing correctly? There is a filter built into the tap, it is known to clog.Did a flow test: ~500mL in 1 minute.† Then disassembled petcock.† Removed filter (kept in-line filter) as a test.

Fuel lines in good condition and not kinked anywhere? My personal trick was to trap the cross feed pipe on an early model R65 with clam shell aircleaner - it flowed enough to trick me for some time, except that the RHS carb would run dry quite quickly at WOT or thereabouts. I felt a 1st class dill when I eventually found it.Verified

Recheck every jet, a minute piece of lint will change the flow characteristics for the worse.Verified, all disassembled and sprayed with carb cleaner

Once you are absolutely sure that your carbs are OK, start checking ignition components - on the well established principle that if you *think* it is fuel it will be electrical - and vice versa.


Took the carbs off and completely disassembled, cleaned, and reassembled.† Same for petcock.† Did a quick tune last night, need to ride it tonight then do a real tune, then we'll see if I've made any improvement to the top end.
  
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georgesgiralt
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Re: Main jets?
Reply #20 - 05/11/18 at 02:14:55
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AhAh !
I see that you have in line filters.
In France they suffer a very very bad reputation giving bikes not apt to attain top speed or top power.
May I suggest that you remove them and test again ?
  
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DadsR65
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Re: Main jets?
Reply #21 - 05/11/18 at 03:56:56
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georgesgiralt wrote on 05/11/18 at 02:14:55:
AhAh !
I see that you have in line filters.
In France they suffer a very very bad reputation giving bikes not apt to attain top speed or top power.
May I suggest that you remove them and test again ?


Exactly the same thought I had.  Might be that two filters in series is too much pressure drop.  I removed the filter in the petcock and left the inline filter in place.  I like to see fuel flow, helps with diagnostics.
  
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Tony Smith
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Re: Main jets?
Reply #22 - 05/11/18 at 16:09:40
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DadsR65 wrote on 05/11/18 at 03:56:56:
I removed the filter in the petcock and left the inline filter in place.†.



In my considerably less than humble opinion, you removed the wrong one.

  

1978 R100RS| 1984 R65 | 1984 XT350 | 1992 KLE500 | 2002 R1150GSA
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Bob_Roller
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Re: Main jets?
Reply #23 - 05/11/18 at 17:28:07
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The filter that you still have installed, is it a sintered element filter, the filter is granulated bass like material that's pressed into a conical shape ??
Another not too common issue, is that the fuel cap is the vent for the tank, my '84 LS sat for 17 years with fuel in the tank, the fuel cap was clogged with fuel varnish, had issues when I got over 50 mph .
Loosened the cap and my power issue went away, soaked the cap in carb cleaner and eventually got it unclogged .
  

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DadsR65
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Re: Main jets?
Reply #24 - 05/12/18 at 05:11:01
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Tony Smith wrote on 05/11/18 at 16:09:40:
DadsR65 wrote on 05/11/18 at 03:56:56:
I removed the filter in the petcock and left the inline filter in place.†.



In my considerably less than humble opinion, you removed the wrong one.




In the long run, I agree.  During the diagnostic phase, I find it useful to see fuel flow (my inline filter is clear).  Once everything is sorted, I'll likely go back to the petcock filter.

  
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DadsR65
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Re: Main jets?
Reply #25 - 05/12/18 at 05:12:42
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Bob_Roller wrote on 05/11/18 at 17:28:07:
The filter that you still have installed, is it a sintered element filter, the filter is granulated bass like material that's pressed into a conical shape ??
Another not too common issue, is that the fuel cap is the vent for the tank, my '84 LS sat for 17 years with fuel in the tank, the fuel cap was clogged with fuel varnish, had issues when I got over 50 mph .
Loosened the cap and my power issue went away, soaked the cap in carb cleaner and eventually got it unclogged .


I've had the issue with the tank cap loosened, so I don't think it's a venting issue.

Inline filter is this:

http://www.euromotoelectrics.com/product-p/ff-451e.htm
  
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DadsR65
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Re: Main jets?
Reply #26 - 05/12/18 at 12:06:08
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Update: disassembled, checked, and cleaned both carbs. Everything looked fine, but I cleaned just to be safe. Set fuel bowl levels at 24mm. Removed filter in petcock since I also have an inline filter. Tuned carbs, rode, then tuned and balanced with manometer.

Bike starts, idles, and runs great. There is still an odd behavior at high speed. Two observations:

1 - at high speed, not much power at 4000rpm. If I want to go faster than about 60mph, I need to wind it up in 4th so that Iím about 5000rpm in 5th. Then I can get to 80+mph (faster than I want to go). Is this typical?

2 - Thereís a flat spot in the power band around 4000rpm at any speed. Iíll shift, then hold throttle about half open. Not much power (but enough to show the engine is still running ok), then after a second or two at constant throttle it comes into its own and starts pulling harder. Maybe needle jet? Maybe ignition/points/advance related?

Also, finally got it registered. Took a couple hours at DMV. Although the website says they only require a VIN check, they made me start it and demo all the lights. Good thing I had put the carbs back on! Nice surprise: no sales tax for immediate family members. DMV lady was excited to see another BMW and showed me the papers from earlier that morning for a guy with a mid-70ís R75. Original title was from Idaho. She even asked to see a pic of my bike.

(Full disclosure:  also posted on advrider.)
  
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georgesgiralt
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Re: Main jets?
Reply #27 - 05/12/18 at 12:35:22
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Could you please test it without the in line filter and report back ?
Also, you set the fuel level in an unorthodox way. The blessed method is to have the flow stopped when the float is parallel to the carburetor base.
  
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DadsR65
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Re: Main jets?
Reply #28 - 05/12/18 at 14:31:14
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georgesgiralt wrote on 05/12/18 at 12:35:22:
Could you please test it without the in line filter and report back ?
Also, you set the fuel level in an unorthodox way. The blessed method is to have the flow stopped when the float is parallel to the carburetor base.


I suppose.  With the filter out of the petcock, it will be unfiltered.

I'm surprised to hear that the 24mm rule is unorthodox.  Seems pretty common, but I can try the "set them level" approach.  Thanks for the suggestions!
  
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DadsR65
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Re: Main jets?
Reply #29 - 05/13/18 at 19:26:08
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Update:  seems that points gap was too tight.  I corrected it and re-timed and bike pulls like a champ now!
  
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