I have this engine on a 2003 scag 52 belt drivin walk behind. The engine has erformed great up to now. Without any load it will sound fine and dandy at full throtle, but when i engage the blades at 1/4 to 1/3 throtle it will almost stall. Then when i push the throttle all the way up, the engine takes about 10 seconds to respond and NEVER REACHES FULL SPEED. During to day it randomly did reach Full Speed, which lasted until the mower was turned off, and i never knew when it would reach full speed again. Any suggestions? Governor?