Vintage BMW Motorcycle Owners

Hey Guys.

I was in the process of starting up my bike this morning when I noticed gas pouring out of what I'm guessing is a vent hole in my right carb. Back in April I had the carbs rebuilt, however I've since then had the bike running several times, so I don't know if the rebuild is tied to this or if it's just coincidence. I've included a pic with the vent hole circled in red.  If anyone has ideas or suggestions as to what is going on here, I would greatly appreciate your input. Thanks to all.... Tom Gelz

Typically it would indicate that the float is hanging up and not rising with the fuel level in the float bowl. Could also be some debris in the bowl preventing the float needle from sealing. Try tapping on the float bowl with a screwdriver handle and see if it stops overflowing.

John Borella
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Nicely explained John

Frank

Thanks John. I tapped on the float bowl with no change. I'm going to open it up today to see if the float is the problem.

I had the same problem and it was the float with my R90S...

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Reporting back to the group on how this played out. It was indeed the float that was causing the problem. When I opened up float bowl, the float appeared to be hung up on something. I could not see what causing the problem so I opened up a spare carb and used the float out of that which appeared to work just fine. I was surprised at the difference between the old float and the defective one which is pictured below. The older float looks to be much more substantial that the new one. Are the new ones coming out of Dellorto just made more cheaply than the originals?

Also, many thanks to Lars, John and Ralph for helping me get thru this.

Tom

Just so you know, your different floats may have different weights stamped on them. This makes them ride higher or lower in the bowl affecting rich/lean. Also there is a critical distance of 17.5 to 18.5mm from the bottom of the float to the bowl seal surface when you gently press in on the float. Old floats are 10 grams, and I think they sell 8.5 gram ones now. You should probably try to make both carbs the same if you can. Consider new needle valves also. They get hard and do not shut off the flow of gas.
Richard Chawes