Carb overflow problem

I have what is probably a self-induced problem with the left side carb on my Rotax. I had the carb of of the engine for some unrelated work in the area of the carb. For most of the work, it sat sideways on top of the engine. At one point it was rolled over onto the overflow tube side such that some fuel came out of the clear overflow tube.

The carb has been reinstalled. With the electric fuel pump on there was no sign of a leak. Soon after starting the engine, I smelled fuel and shut it down immediately. Now even when under just the pressure of the electric pump, fuel is streaming out of the overflow tube.

Amy ideas as to what could be causing this? Could the floats be jammed in a position that would cause such flooding?

You may have a stuck float or the needle valve is slightly off kilter and not sealing properly. You have two choices and the first isn't very scientific, but does work at times.

First take the plastic end of a large screwdriver and whack the carb body on the bowl and carb body a 4-5 times. Whack it sharply, but you're not trying to knock it out of its socket. Then try running the engine again. If it clears up your good to go. If it doesn't work you'll have to pull the carb and see why the needle valve isn't seating or the floats aren't controlling the level. If the carbs are out of sync bad enough the engine will shake and cause fuel to vent too.

Dave sound like the float is hung up. Rogers idea used to work for us in the automotive field working on Holleys and Quadrafloods.
Tom

If the tapping knocks the float loose, will the effect on the overflowing gas be immediate, or do I have to wait some period of time after the tapping?

Dgamble said:

If the tapping knocks the float loose, will the effect on the overflowing gas be immediate, or do I have to wait some period of time after the tapping?

Click to expand...

result should be immediate but I would suggest taking the bowl off for a proper look

roger lee said:

You may have a stuck float or the needle valve is slightly off kilter and not sealing properly. You have two choices and the first isn't very scientific, but does work at times.

First take the plastic end of a large screwdriver and whack the carb body on the bowl and carb body a 4-5 times. Whack it sharply, but you're not trying to knock it out of its socket. Then try running the engine again. If it clears up your good to go.

Click to expand...

This time honored technique has worked on everything from tractors to....Airplanes! I have also overhauled many starters with that special overhaul hammer.

Fixed!

Thanks for all of the help - the advice provided here was spot-on. The problem was not with the floats themselves, but it was similar: it seems (I will never be 100%) sure that the float needle may have been stuck. When I took the float bowl off again after ensuring that the floats were okay but still had the problem, I did two things differently: I exercised the float needle up and down a few times, and when I replaced the bowl I tried to keep the carb as close to upright as I could to preclude the float needle from maybe getting sideways again.

Longer version:

http://www.schmetterlingaviation.com/2013/11/blonds-and-carburetors.html

In a few days I'll share what it was that had me take the carb off in the first place.

Priceless!!!!!
Tom

+1

What Tom Said!!!!!

The floats in the Bing carbs on the 912 seem prone to sticking. We got in the habit of checking them every 50 hr or annual, whichever is first (you'd better be flying > 50 hr/yr!). Amazing how little debris is required to make them stick.

TODR

The floats rarely stick unless they are old and worn, starting to sink or the pins they ride up and down on are bent and allows the float to rub on the side of the bowl.