[chaos]

It can't run without fuel and air. It has to **** air past a place where it can **** fuel. I can't find a drawing of that carburetor. Are you absolutely positively sure the carb is ALL the way closed? Does it have a throttle stop? Maybe it's defective. I think the carb has to be the problem.

Unhook the ball at the servo end of the throttle linkage so that you can move the pushrod by hand. Move the pushrod to close the throttle all the way.. go as far as it goes. Then see if the servo end of the link matches the servo position when you go to cut-off. If the servo is actually pushing the throttle arm all the way to cutoff, pull the engine and see if that position actually closes off the carb hole fully. There might be a flake of metal that's preventing the thing from closing off completely.