The New And Improved Unofficial R65 Forum V2

Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Julio A. on March 25, 2011, 09:36:53 AM

Title: Setting up the A/F mixture
Post by: Julio A. on March 25, 2011, 09:36:53 AM

I already inspected and made sure that my piston rings are still good. I already properly overhauled and cleaned my carburetors. Still, When I set up the A/F mixture screw to the repair manual's recommended spec to 1 and 1/4 turn from fully tightened, My spark plugs still gets a healthy coating of black soot. I'm quite unsure on what to do beyond what the repair manual tells me to do.

I leaned the mixture for about a half turn and the idle went up, still, the plugs are coated black. The thing is surprisingly running fine even with all that soot in the engine. Looks like the new plugs are that good.
Should I still adjust it to be leaner? I'm afraid of going far from the recommended spec.  

Title: Re: Setting up the A/F mixture
Post by: Barry on March 25, 2011, 10:04:48 AM

Quote

Should I still adjust it to be leaner? I'm afraid of going far from the recommended spec.

Not sure where you got the spec of 1 and 1/4 turns out Julio. It should be more like 1/2 turn out or 3/4 at the very most most.

As it's best to start rich and adjust by turning in to weaken try starting at 3/4 turns out and work in towards 1/2 a turn. You should find a sweet spot in between somewhere.  If it doesn't stumble keep going all the way to 1/2 a turn.  For the most part you are only setting the mixture at idle and small throttle openings with this adjustment so it's safe enough and may explain why it has still been running well.

Title: Re: Setting up the A/F mixture
Post by: Rob Valdez 79 R65 on March 25, 2011, 05:30:14 PM

Yes - page 32 of the PDF (P 79 of this manual):
http://www.bmwr65.org/htdocs/yabbfiles/Attachments/R65OwnersManual_001.pdf

Title: Re: Setting up the A/F mixture
Post by: nhmaf on March 25, 2011, 09:23:47 PM

Common practice is (with warm engine) to adjust the air mixture screws so as to produce the fastest, smoothest idle - with the 81-84 bikes this generally is somewhere between the 1/2 turn and 3/4 turn out position - assuming all else is OK and no air leaks, etc.

I'd nudge yours down to 3/4 turn and see how it goes.  Replace the plugs or at least take yours out and give them a good cleaning and see how it is after some miles.

Title: Re: Setting up the A/F mixture
Post by: Julio A. on March 26, 2011, 09:08:52 AM

I had another attempt with it this afternoon.

At 3/4 Turn, It doesn't really idle very good, it gets worst as I get near at 1/2 turn where the cylinder does not fire at all.

It started to idle better as I got to the midpoint between 3/4 and a whole turn. I stopped there.

I'll take it for a spin tomorrow, I already cleaned the plugs yesterday. I hope this fixes it.

BTW, I noticed something odd on my choke, RPM's will go down and the engine feels out of tune when it is on. It hasn't done that before.

Title: Re: Setting up the A/F mixture
Post by: montmil on March 27, 2011, 04:47:34 PM

Julio,  Check out this carb synchro article. It might help you out. Best I've ever seen and written in a style that even I can understand.

http://www.airheads.org/content/view/183/98/

Monte

Title: Re: Setting up the A/F mixture
Post by: Teo on March 27, 2011, 09:48:08 PM

Julio,
The choke is working properly.  After the engine is warmed up sufficiently the RPMs will down and the engine will stumble a bit or run ragged with the choke on.  It is a too rich situation.

Teo