I am working on the Toro S-620 1985 snow thrower. I cleaned the carburetor and have it started and running. On the side of the carb are two adjusting screws. I figured on was high speed and the other low speed. However the blower only runs at full throttle, there is no speed control. What then do the adjusting screws do? and how are they to be adjusted? The IPL say's that one is the Idle Adjusting screw the other is the main adjusting screw. The engine is a Tecumseh (sorry I don't have the model number right now) two stroke engine. Any advise will be greatly appreciated. Have a happy holiday's.