Since new have always had a slight amount of fuel leaking into the carb air box after shutdown.After 24 hours engine starts even in cold weather the engine starts with no priming.A light spray of fuel is evident on the aircraft undersuface after flight..If the engine is shutdown turning off the fuel cock,none of this happens.Several times recently when I turn on the fuel cock there is a constant flow of fuel through the carburetor.This carb is has done 100 hrs from new.Engine from aerosport power.Ideas please.Thanks,Ron.
fuel leak through carburettor
- Thread starter ron
- Start date
mike mcs repair
Registered User
chugiak AK
there's an old thread on here somewhere.... about fuel coming down out of intake tubes/system after shutdown
you might have float level not right?
the getting stuck on turning fuel on, is probably because you are shutting fuel cock off and running it dry and leaving it like that, and needle buildup sticking it?????
you might have float level not right?
the getting stuck on turning fuel on, is probably because you are shutting fuel cock off and running it dry and leaving it like that, and needle buildup sticking it?????
X2 on float level/bad needle valve seat
I once watched a carb guru work his magic on an O320 carb, he made a gizmo that would screw into the bowl drain threads, it had a rigid clear tube that bent up along side the bowl. It was marked to indicate correct fuel level/float height.
this enabled him to check float level on a carb while still mounted on the aircraft. Also to confirm float level on pressurized fuel system.
Not that this will lend itself to this situation but got me thinking about it.
I once watched a carb guru work his magic on an O320 carb, he made a gizmo that would screw into the bowl drain threads, it had a rigid clear tube that bent up along side the bowl. It was marked to indicate correct fuel level/float height.
this enabled him to check float level on a carb while still mounted on the aircraft. Also to confirm float level on pressurized fuel system.
Not that this will lend itself to this situation but got me thinking about it.
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cubpilot2
SPONSOR
Anchorage Alaska
I just went through the exact thing. After lots of pain we finally found that the primer pump would not seal off completely and fuel flows into the cylinders when shut down and while running. This happened very slow and the fuel would evaporate in the box and leave sticky blue goo. The engine would run a little rich. Alway had fuel stains. Installed a new primer pump and all is well. No more leaks and the fuel consumption has improved.
We spent a lot of time and money with carb swaps and experimentation. New pumps are expensive. We thought about lapping the seat but didn't want to take time. To test this out; cap off both primer lines (to and from the pump).....we did both anyway. Clean the air box good of any residue and go fly. You should see immediate results.
The pump problem was not with the o-rings but the needle / seat in the bottom.
http://www.supercub.org/forum/showthread.php?50489-Fuel-Stain-mystery&highlight=Mystery+fuel+stain
We spent a lot of time and money with carb swaps and experimentation. New pumps are expensive. We thought about lapping the seat but didn't want to take time. To test this out; cap off both primer lines (to and from the pump).....we did both anyway. Clean the air box good of any residue and go fly. You should see immediate results.
The pump problem was not with the o-rings but the needle / seat in the bottom.
http://www.supercub.org/forum/showthread.php?50489-Fuel-Stain-mystery&highlight=Mystery+fuel+stain
cubdriver2
FRIEND
upstate NY
Funny, carb guru. Buy a barbed fitting that screws into bottom carb drain hole and clear vynal tubing. Measure float/fuel height on level carb half matting surface.
Glenn
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Good of point on primer leak. However, Op reported "constant fuel flow thru carb" when fuel valve was reopened.
im assuming more fuel than could be delivered thru primer system.?
"carb guru" status ;-) to my mind, occurred when I entered the guys shop. WW 2 era fluid filled diagnostic instruments lining the walls to the ceiling, flow bench, pressure/vacuum chambers and the like.
He attached his little float level tester to demonstrate the effect that fuel pressure has on float level. What do you suppose happend as he dialed up fuel pressure on MA-4?
Btw. Float level tester needs to be rigid tube if it's going to be calibrated, but yes, simple to make.
im assuming more fuel than could be delivered thru primer system.?
"carb guru" status ;-) to my mind, occurred when I entered the guys shop. WW 2 era fluid filled diagnostic instruments lining the walls to the ceiling, flow bench, pressure/vacuum chambers and the like.
He attached his little float level tester to demonstrate the effect that fuel pressure has on float level. What do you suppose happend as he dialed up fuel pressure on MA-4?
Btw. Float level tester needs to be rigid tube if it's going to be calibrated, but yes, simple to make.
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Correct Oliver the flow through the carb would be max demand rate,hence one would probably attribute this to the float stuck in the full down position or sticky float valve?
skywagon8a
MEMBER
SE Mass MA6
Thanks Pete,We will be dismantling carb next week,interesting this is the second new carb we have fitted in 200 hours..Aerosport power replaced the first one as we couldn't solve the mixture problem with the 0-375 engine.
Gordon Misch
MEMBER
Toledo, Wa (KTDO)
Suggest you contact (pm) Aviationinfo on this site - he had a difficult-to-diagnose leaking carb issue that is since resolved, but I don't recall what the solution was.
cubpilot2
SPONSOR
Anchorage Alaska
Sounds so much like what we went through. Changed a needle and seat, Tried a different carb. Had the first carb overhauled. Then my friend bought a factory overhauled carb. This was over two - three years. All had the same issue. Slow learners I guess. Always had the stain and drippings. Never had it "run out" thou. In the winter you would see stain on the snow unless he turned off the fuel
I'd still test the primer before spending lots of $. It won't cost a dime to find out. If it still leaks then you for sure have a carb issue.
Good luck
Solution��Cheap as and as so many of you knowledgeable guys suggested.Took the primer out,cleaned ,crc(plenty of!)fuel lube on the shaft .A light lube on the O rings and refitted.Now no sign of a seepage overnight. The other problem has not reoccurred,that is when I shut the engine down by turning off the fuel cock.When I then turned the fuel cock on again,fuel poured out the carb air box.We suspect the float (new style) was sticking in the demand position,but no proof.Reset float levels and no more fuel spotted belly on the cub.Thanks guys! Ron.
