I do not remember which YF you have. Is it manual or automatic choke?
If automatic choke, is the choke butterfly acquiring a vertical position (wide open).
If the choke is not going wide-open, the engine could load up, causing stalling. If the engine is hot, then pressure in the fuel line will dump some fuel into the bowl, raising the level above the main discharge nozzle, and it will then drop down onto the throttle plate, and run out beside the throttle shaft.
However, dirt is a distinct possibility anytime you loosen and tighten old fittings on an old fuel line.
I would suggest acquire a helper; then start the engine, and run it at a fast idle until the engine warms. Now have the helper slide a piece of Masonite (or similar substance) across the air intake (while you are running at a fast idle) causing the engine to stall. Now restart, and see what happens.
Jon.
