I've been running my rebuild 12a for over a year now, and i've always had a problem with the shutter control valve. I have to plug the air inlet for the shutter control valve (which connects to the air cleaner) just so it runs ok. Otherwise (unpluged), the moment I rev it up i can hear the shutter control valve activate and the engine has no power and will struggle to rev up.

On top of that the engine has always had a lumpy idle, i tried everything... playing with the timing, the fuel/air mix and idle screws and even got another carb from the junk yard, and the same thing.

Last thing, when i initially press the throttle the engine chokes (kinda gasps) as if it were to stall... so i have to tap the throttle and then press it down when starting from stand still.

any suggestions will be greatly appreciated

thanks