Re: throttle problems
most probable cause is an airleak, either at the carb or the manifold.
first, make sure your idle screw is set correctly. screw it in by hand till it stops, then unscrew it 3 to 4 full turns out.
next, make sure your throttle cable's not binding anywhere.
take your air filter off, and look at your carb and make sure your slide opens all the way at full throttle (with the motor off) and goes all the way down when the throttle is released.
make sure your slide is seated in it's little groove inside the carb.
if all that stuff is working right, then get some carb cleaner and spray it around the manifold, (engine running) where the carb goes on, and at the engine. if there's a leak, it'll rev up, or sputter and die.
do you have an O-ring in between the carb and the manifold?
you might need a new intake gasket.