idle mixture screw, no response

[JJH]

1979 BMW R65
I recently went to balance my carbs.  I warmed up the bike with a ride, then went to adjust the idle mix (screw on the bottom).  There was absolutely no change.  Did not matter whether,  all the way out or all the way in.  Okay, I pull the carb cleaned it up.  Pull all the jets, and screws.  Actually it looked pretty good, since I rebuilt the carbs about a year ago.  Sprayed cleaner through all the holes.  Everything looked good.  Placed it back on the bike, and there is still not change.  The question is, did I miss something?  Is there anything else that would cause this lack of response?  My ego can handle it if I just didn't clean enough, but I really thought I did a pretty good job.  Frustrated in Missouri.

John

[Barry]

Normally you would say the most likely cause is a blocked idle jet but there are other possibilities.  

Just thinking out loud what could cause the problem:

 - a lack of fuel inferring a blockage but then the fuel for idle has to come from some place else.  For the mixture screw to work it has to be the sole source of mixture at idle so if the enricher was even slightly on or wrongly assembled that would swamp any changes in the mixture screw. A very quick way to eliminate that as a possible cause would be to tape over the enricher outlet in the venturi.

 - a lack of airflow past the idle mixture outlet into the venturi, again air flow has to come from some place else like  an air leak. The mixture screw needs air flow under the throttle plate so if the throttle plate was closed that could be a cause although you wonder how it could then idle at all.

[JJH]

Barry,
I am still trying to understand completely how the Bings work and you are being a great help.  
1.  Idle jet.  I made sure this was clean with carb cleaning flowing freely through the jet.  Test by cleaning this again.

2.  The enricher.  I need a bit of education here.  Let me see if I have this correct.  When the choke lever is off, it should contribute no air or fuel to the intake.  If this is true, the only source of fuel would have to be from the idle mixture... And if the idle mix screw is all the way in, and the choke lever is off the engine (or at least that side) should not run.  Since it does run fuel may be coming from the enricher.  Test this by closing off the enricher port.  

3.  Maybe there is fuel from the idle mix, but there is no air/ and the air is being supplied from another source?  I guess I don't understand the system enough to understand this possibility.  Test by ?

Sorry for all the questions still trying to work on my troubleshooting skills.

John

[Bob_Roller]

I had the same  issues with my R65's over the years .

I would remove the idle jet place tape or what ever you have over the holes drilled in the tube of the jet, there are 4 holes .

Take a can of carb cleaner with the extender ' straw ' installed, spray the cleaner in the hole with the screw driver slot .

If the jet is clear carb cleaner it will come out of the very end of the jet, that is the metering orifice, not the holes in the sides of the tube .

I was fooled by cleaner coming out of the side holes and I was sure the jet was clear, I was wrong !!!!

I have not had very good luck getting that orifice opened up, tried soaking in carb cleaner for a few days, cut a very fine wire on an angle and use it as a ' drill bit ' to clean it out, using an ultrasonic cleaner, all methods didn't work very well, I purchased replacement idle jets .

Even when this hole is open, it is quite difficult to tell .

[JJH]

Bob, thank you for your suggestion!.  I did find out that I assembled the enricher incorrectly.  I placed the plate 180 degrees out of phase.  I corrected this but, then the whole family life got in the way of testing everything.  I know one day I will look back at spelling words for my kids with happiness, but right now I just want to think about carburetors

[JJH]

Update-
The pilot/ idle jet was fine.  It was due to the enricher.  The gaskets had pulled into the "cove" in the enricher on both sides.  When putting back I placed the plate in 180 off, on one side.  Fixed both issues.  Also I checked the diaphragm and one was dis-formed.  I did not see any holes but I replaced it anyway.  So now I have an idle mixture response on both sides!  

[Barry]

A pulled in enricher gaskets is not uncommon and probably due to the cover not being truly flat.  I suspect they like that from new. Any time they are off it's worth resurfacing them using fine wet and dry abrasive paper on a flat surface.