Carb Issues

[Gibson]

Easy way to tell if it is carb issue or ignition. Spray a bit of carb cleaner into the not firing side while its running. If it picks up and fires, you know its not ignition or compression issue and you need to get that mixer cleaned out. It does not take much of a clog to run really bad.

[arzueck]

Rob - I do have the wonderful original toolkit. No BMW manual but I have the Clymer.

Update:

I've done a compression test and confirmed both cylinders in the "good" range. So that's good. I have spark. I have not done a timing test - trying to borrow a timing light rather than buy one.

So I'm still stuck on the carbs. I just took the float bowls off: Right side 16mm fuel level, left side 18mm (ish). They seem to be functioning correctly (fuel flows fine when i push up on the floats) though maybe they need adjusted? Confirmed the little jets in the corner of the float bowls are free and clear.

Thanks for the enrichener info. I have NOT taken that part of the carb apart. I felt like it was running with the choke (enrichener) on, and not with it off, so that isn't the problem area. Maybe that's flawed logic. I might go ahead and do that later this morning.

Another question. Something that has confused me since I started in on the carbs, on the attached photo, the blue arrow points to the mix screw. The red arrow should be the idle stop screw? This screw has absolutely no adjustment to it. If loosened at all it is wobbly in the threads and I'm sure would just rattle out. It seems to have no effect on how the carb runs. The diagrams Clymer gives have a different looking screw with a spring assembly of some sort, but they are using a slightly different model of carb I think. Thoughts?

[arzueck]

Here's the photo...

[arzueck]

Also, for fun, here's a photo of the bike from this morning:

[barryh]

The red arrow points to the vacuum take off of point for balancing the carbs.

The throttle stop screw can be seen on the inside close to the throttle cable with the adjusting screw pointing upwards.

Your carbs are known as "flat tops" but all the adjusting screws etc are in the same place as a "dome top" carb.

[Kurt in S.A.]

Barry -

The throttle adjust screw doesn't look anything like my "non flat top" carbs on my '78 R100/7. Are you showing a type 94 carb? I see from the Bing manual that what you show was for the type 94, 64-2 (flat top), and 64-3 carbs. Were they that different on the flat tops? My /7 has the throttle adjust screw access from the bottom...AFAIK it's just a type 64.

Hmmm...might have answered my own question!!

Kurt in S.A.

[barryh]

Kurt,

My flat tops have throttle stop adjustment screws pointing upwards.

Yes it was a picture of a 94 carb and just the first thing I found that showed the throttle stop screw on the inside with screw upwards.

[SteveD]

The carb Barry shows is from a R100S.
Looking at the OP's pic, I think his throttle adjust screw should be the same because I can see the throttle arm behind the air mix screw.

[Rob]

I used to have '79 R65 with flat-tops. Throttle adjust screw facing upward.

[arzueck]

Hey guys - throttle adjust screw is on the bottom - I was right about that one. I was confused about the idle stop - it is at the end of the cable linkage (duh!) on the inside (engine side) of the carb facing upwards. I have the 32mm flattop.

Anyway, I've gotten the left side working nicely. The right side is running okay with the choke set, but as I slowly let the choke out it starts to backfire and die. It even wants to backfire once warmed up with choke on. What gives?