by Squeazel » Thu Dec 20, 2018 12:42 pm
I didn't mean drill out the jets- those are calibrated as to hole diameter and just need to be unscrewed and cleaned. But when the carb is manufactured, there are lots of channels drilled in the body that can't be drilled straight from one direction. Those are drilled in two stages- once in one direction and once again in another direction, to connect the two places with a channel through the carb body. They'll have a brass dome cap on the outside of the body where the two holes were drilled from the outside, to seal the holes from the outside. Professional carb rebuilders will drill out those caps to access the holes, clean them, then put a new cap back on. You'll see a bunch of those caps on your carb. Even if I knew where to get the new caps, I wouldn't trust my ability to seal them properly after replacement. So I just either work a wire through all the holes I can find, and if that doesn't work I say "screw it" and buy a new carb.
From your symptoms, I'd say it's the idle jet passage that's blocked, which runs from the idle jet to the mixture screw, to a tiny hole in the throat of the carburetor on the manifold side of the butterfly. At closed throttle, the fuel is sucked through the jet from the bowl, metered by the mixture screw, then it squirts through the hole in the throat. There's another hole that allows air through; I don't think that one is blocked because blocking off the air with your hand makes it run; it's getting plenty of air.