82 BMW 65 LS high idle

[montmil]

I have just reread this entire thread, twice; mainly because it's pretty interesting. However, I have an opposing thought regarding advice on the tuning of the idle air screws. I must have missed this when it was posted earlier...

...I would try turning each clockwise a specified amount, like 1/8 or 1/4 turn each, that will lean out the mixture...

I'm of the opinion that the clockwise, or closing, of the idle screw will actually increase the idle speed due to the richening of the mixture. All my Bing CV tweaking research indicates this to be correct. However, for the sake of intelligent discourse... Here's a scenario to consider:

The idle air screws control only... air. There is no fuel passing through this circuit; just air. So, with a given idle air setting that theoretically provides a 50-50 ratio of air to fuel, then closing the air screw -turning it clockwise- would thereby richen the mixture due to less air in the fuel/air mixture and thereby likely increase idle rpms.

I risked my 81's sweet carb synchronization job just to confirm this theory. Closing the idle air circuit screw by 1/8 turn -clockwise- raised my R65's idle rpm -I have a digital tach. Returning the screw to its original position, then opening the idle screw 1/8 turn -counterclockwise- from the synch'ed tuned position lowered the idle.

I'm no expert and I'm always open to learning experiences.  [smiley=2cents.gif] Comments?

Monte

[Ed Miller]

On my Amals you could call them idle air screws, though I think they're actually called pilot air screws.  But on CV carbs they control fuel flow, so turning them in leans the mix.  I have to remember that between the two bikes, but that's the least of the differences!

I believe that on the R50/5 and R60/5, they used slide carbs which also had the mixture screw controling air, like on my Amals.  And I bet they had ticklers too.

[Bob_Roller]

I'll check the Bing manual when I get home this afternoon .

I don't get involved with the carbs that often, and the last time was 2 years ago .

I'll definitely get current again when the carbs for the LS get re-built in about a month, when the temps hopefully will not be getting to the 100 F. mark .

[montmil]

I'll check the Bing manual when I get home this afternoon.

Cool, Bob.  Got a few Airheads members that will probably flame me should I dispute their word but, hey.... Interesting to say the least. And I did achieve the results noted in my "theory" posting.   Monte

[Bob_Roller]

I was looking for an email address for the Bing Agency, I figured they would be the definitive authorities on the subject, but I can't find an email address on their website, I'm at work, and it won't let me access it .

[Bengt_Phorqs]

Here you go.  www.bingcarburetor.com

I need to go back and re-read these carb threads myself.  Rebuilt the carbs on my R90/6 and have them adjust just fine.  Runs like it ought to.  Just finished the rebuild on the R65, and aside from the problem with the main jet venturi, the bike runs well but I can't seem to get them sync'd and there is either a fast idle or a stall.  Same diaphragms and o-rings on both bikes.  The carbs are very similar so why can't I get it smoothed out?  Hmmm, things to ponder on....

[Bob_Roller]

Thanks for the link, but when I click on the email on the top of the page, I get the no email service set up .

[Bengt_Phorqs]

Maybe the suits are trying to make sure that we do some work.
bing@bingcarburetor.com  Try that one.

[Bob_Roller]

Thanks, I'll see if I get an answer today .

[Bob_Roller]

Just got a response from the Bing Agency, their response, the mixture screw, is the idle air adjustment  .

I'd really like to get a 'circuit' diagram of the 64 series carbs, just to see where all of the passages go, and do !!!!

[Barry]

Bob, here's my take on it.

It is correctly called the idle mixture screw because it controls a mixture of air and fuel at this point in the Bing CV Carb.  There is an idle air inlet jet (just a hole which is not replaceable) at the carb inlet and a cross duct which provides the air to mix with the fuel passing through the idle jet.
The idle mixture screw controls how much of this mixture is admitted to the carb venturi although there is also a 2nd transfer port involved just to add confusion. Anyway this mixture mixes with the small amount of air passed by the throttle plate and that is why screwing in the idle mixture screw weakens the overall idle mixture and screwing out makes it richer.

BTW before anyone shoots me down in flames this is not actually a Bing CV carb. It's close enough though and the best diagram I can find to illustrate how a Bing CV works.

[Bob_Roller]

Thanks, Barry, that gets things a lot clearer on how it works .

I thought I knew how the Bing's worked, but I was way off !!!!!!

[Barry]

Here's an article that describes how Bing Cv's work much better than I can.  It was written back in 1978 shortly after they were introduced on airheads.  The point about premixing air and fuel in all of the carb circuits is well made but the illustrations don't show this well which is why I posted the other diagram.

[montmil]

All this chit-chat about high idle speeds must have been absorbed by my '81 R65 as the revs had just recently begun to be slow to drop, or just remain elevated, on a regular basis.   [smiley=naughty.gif] Urrr... tiny fists of fury.

Then, a small wattage bulb clicked on over my head; refrigerator size...

My recent bean can "failure" -which turned out not to be a failure but simply a crushed and broken wire/s- required removal of the trigger unit for the wire repairs. After splicing in new wires, I stabbed the can back where I thought it looked right and rode on. Oops.

My new Actron timing light showed that the can was positioned in a well advanced location. Retarded that puppy and idle smoothed out. It's true... an idle speed near 1400 rpm touches the rev point where the advance mechanism begins its function. Messing with the carbs is futile unless the timing is set to specification.

BTW, the new Actron timing light did a fine job in throwing a focused beam that lit up the flywheel marks. No more working in the dark with the vintage Sun tool.

Monte

[trolle]

Very good article, for the first time I have a feeling that I maybe understands the principle of the CV-carb.

greetings from a grey, windy, and precipitating north