Mikuni trouble

[gusm2]

I was running at Santa Pod yesterday during my burnout I noticed a fuel leak from around the carburettor, back in the pits I found it to be coming from the brass vent tube just above the fuel inlet, I removed the float bowl and checked the float height....way to high
I adjusted it and tried again now it was still coming out of the small diameter plastic pipe when giving full revs, I put a small cable tie around that and tucked it out sight
Every thing is clean inside the carb and the needle jet
Any ideas or suggestions

It's a mikuni HSR 42

[nijine]

Not an expert but if it’s possible to lower the float any further, that might be it. There’s a pretty tall brass pipe that connects to the plastic overflow pipe, so if the fuel level in the bowl is getting that high then that might be it.

[sungod]

Wondering if when you do your burnout do you rock the bike side to side or hard launch forward? When checking the float height make sure both floats are set the same. 18mm +/- 2mm.
Any chance the fuel in the bowl is sloshing around and getting into the overflow tube? Last thought is there a lot of vibration that can cause the inlet needle to unseat?

[rejeanprimeau]

Check your gas cap vent.

[mikeLI_77]

Every time my mikuni has leaked from the overflow or vent it was due to the needle not seated correctly due to either some sort of debris or it possibly deteriorating. I have had it look fine and I cleaned it and it still leaked. Each time it happened I ended up changing out the seat and needle the float bowl pushes up to stop the gas flow and that has fixed my problem.

[gusm2]

Thanks for the replies folks

[Iron Mike]

Check the condition of the oring on the back side of the needle seat.