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[Old trials fanatic]

I've got an OSSA TR77 that i'm doing up at the moment and it's a 250. Got no carb on it but i have a Bing off a 350 TR77 so i was going to fit that. Just wondering if anybody knew the jet sizes for the 250 as i assume they are possibly smaller than the ones for the 350 ? also the carb is leaking petrol. Now i thought it was flooding but after stripping and turning upside down the float needle seems to be sealing ok when i blow through the fuel pipe and there doesnt seem to be any fuel in the float which would normally indicate a punctured float. The float needle valve doesnt seem to be worn either. So only other thing i can think of is the gasket for the float bowl. Are these known to be problematic? All helpful suggestions gratefully received

[Dadof2]

Following is a bit messy but worth a try. Remove the carb and tank from the bike, then with the float bowl off turn the fuel tap on and see at what float position / height the flow into the carb actually shuts off. Also check the floats are not catching any part of the bowl or jets that is resricting their movement.
Cheers