The Cessna 120-140 Association Forum

I went out and flew today and when I was doing my postflight I noticed a drip of fuel on the end of the fuel mixture screw. The aircraft ran fine and idled smooth. Its a Stromberg carb on a C85. Any thoughts?

Nothing?

I'm thinking it's coming from somewhere else. The only time fuel is in the area of the adjusting screw is when the throttle is mostly closed, in which case it is under negative pressure and not likely to drip out. Do you shut the fuel valve off? If so, the fuel level in the carb should be much lower than the screw. (If not, and your float valve leaks, I'd expect you'd see it all over the place, but not on the idle screw anyhow. Plenty of bigger holes to leak out of lower on the carb.)

No chance it's water, is there?

I too found it odd that it could be dripping out of the screw area for the reasons you stated. Its definitely fuel. It could be dripping from above, but it would have to be coming out of the intake tubes maybe? I will check it next time I fly and see if I can see if anything above the carb is wet. Like I said it runs fine. Thanks for the feedback.

Joe

Are you using 100LL? One benefit is it leaves a nice blue stain.

Does the drip form immediately upon shutdown, continuously while the engine is running, or only after you wait for an interval?

I just happened to see a drip when I was doing my postflight. I haven't observed it while running. Looked like there may have been a drip or two on the inside of the cowling but nothing major. This was after an hour flying.

If you shut it down with the ignition, it will draw extra fuel as it winds to a stop and it has to go somewhere.

I will try just shutting the fuel off and letting it shut down that way and see what happens. Thanks.