Diagnosing a carb problem

[Rob Frankham]

Next time the bike cuts out, make a note of what is going on elsewhere in the bikes electrics. Do any of the idiot lights come on before the engine actually stops rotating? Are they acting as normal when the bike is stopped in failure mode? Are the vehicle lights working as they should? Observing what does work (and what doesn't) can give a valuable insight into where the problem lies.

Rob

[pdx_r100s]

I solved the problem. The floats were sunk and there was too much fuel in the bowls. It must’ve taken a a minute or so to overfill, and I guess when I shut off the petcocks I wasn’t seeing the fuel leak out of the carb.

I put new floats in and it runs great.

[gspd]

oops!

[gspd]

it's funny you never got gasstinkboot.
Luckily you had new floats on hand.
Could you post pics of the old ones?
I'm curious as to which type they were and their condition to have caused those symptoms.

[Rob Frankham]

Also, what is the ethanol concentration in the gas you use?

Rob

[barryh]

Floats don't have to look particularly bad to be sinkers, they just absorb fuel and get heavy. By the time they reach 16 or 17 grams they are sinkers. When I had that happen the bike ran fine except when I came to a stop at a junction or lights when the idle speed would be ok for a few seconds and then start to fall eventually stalling if you didn't blip the throttle. New floats cured it. Fast forward 6 years and those new floats must have started getting heavy again as the idle symptoms returned. Adjusted the float levels to compensate and the idle is stable again. Basically the floats are not really up to the job long term and a bit expensive to be replacing them too often.

[Kurt in S.A.]

Oak always suggested putting the floats into a container of gas. If 1/3 of the float was above the gas line, the float was generally OK. I think Snowbum did some float-weight testing years ago...might have posted about it on his website.

Kurt in S.A.

[melville]

Now that I'm not in CA, I try to buy non-ethanol gas when I can. It's about 60 cents to $1 more expensive per gallon. I also shut off the fuel taps about a mile from home and let the bike idle on the centerstand in the driveway to drain the bowls before parking. Particularly if the bike is going to sit a while before the next ride.

[gspd]

The main symptom I've experienced from heavy sinking floats is "gasstinkboot".
I've seen many bikes seemingly running 'normally' even while gas was seeping, dripping, or pissing out of the overflow.
I've also seen heavy saturated floats lighten up again after being left lying around for a while (many months?) .

[pdx_r100s]

Sorry that I don’t have pics—I threw them out before I came back on the forum. They were a medium brown—not super dark. I saw the pics on the snowbum site, and they weren’t as dark.

I was using his method to check float level with the bowl off and all seemed good. But when I put the bowl on and tested, it overflowed. Maybe it was doing this before and I didn’t notice the gas spilling out? It overflowed once a few weeks ago, but I thought it was just a stuck float needle.

I removed the floats and tested them by floating in a jar of gas, and sure enough only about 2mm of the float was above the fluid. Definitely not a third. It is interesting that it went into total failure mode only after I rebuilt the carbs…maybe something else that I did enhanced the problem.

There’s a bmw mechanic in town that stocks parts—I picked up new floats and now the bike is riding great.