Also try the procedure on the Sea Foam instruction label to clean carbon deposits from your combustion chambers - with the engine idling, slowly pour Sea Foam directly into the throttle body air intake (give it some slight throttle if necessary to keep it idling and prevent it from stalling out). Immediately turn off the engine and let it sit for 5 minutes. Restart the engine and rev it up - there will be a lot of white smoke. Continue to rev the throttle until the white smoke clears and the exhaust returns to normal.