[aeroace]

LOWER YOUR IDLE SPEED

The CFM rating of your carb doesn't matter(750 vs 850). Idle speed does. If your plugs are too hot, or too much carbon buildup in the combustion chamber, these could be the cause. These form hot spots that act like glow plugs and ignite the mixture. Don't over richen the idle mixture to try and correct; it'll cause more carbon buildup.

If nothing else works

DRAG THE CLUTCH WHEN KILLING THE MOTOR

LEAVE AUTOMATICS IN GEAR UNTIL DEAD, THEN SHIFT TO PARK