I agree with Jay that the problem is probably due to something in the choke (mixture control) set up. This can happen if the mixture pinion gear is meshed at a different location on the needle gear rack (than it originally was) or, if you removed the pinion shaft lever, it may be in a different position now. I would also check to make absolutely sure that the air valve floats without restriction. I did have to fiddle with the pivot arm position as I recall. I can take some closeup pictures of how I have mine set if you like Pete.