spongehead--

A carb swap may solve your problem if off a similair 3.5 engine--too
much work though. You mentioned your throttle adjustment was
frozen--you might try advancing the control wire (pliers might help)
toward a faster run postion to get away from slow idle.

If this doesn't work--carb cleaner would be my next attempt at solving
the problem. Squirt it every where (in and around the carb.)

Lastly, as your time and parts cost creep higher and higher--don't
forget a new 3.5HP mower is only $99. ;-))

Good Luck

Tut