I have a 1991 ski-doo scout 377 i have been trying to get going. I am having trouble 1/8-1/4 throttle. It will "blub" a little. It will idle o.k. and 1/4 to WOT in runs great. I have cleaned the carb (twice), checked float height, checked jet numbers, cleaned the fuel pump, and installed an inline fuel filter and new plugs. When i adjust the idle air screw (witch should adjust idle up to 1/4 throttle) i do not get much engine change. And does not seem to change 1/8-1/4 throttle. I also adjusted the needle, leaner one notch witch didnt seem to have any effect. My next move is to do some plug testing and see what i get. Something i did notice is there is a crack (pretty wide) in the air box right next to the carb flange. Could this be my problem? I Any suggestions? FYI: it has a mikuni VM34 carb.