I hope that you are not putting any premium gas. These engines are designed to run on regular 87 octane fuel. The only time that you might need higher octane fuel is if you have replaced the computer chip that advances the timing in order to get more power out of it; if you don't you are just wasting money. Just make sure that you use good brand gasoline (Top Tier) and not ethanol blends. Keep in mind that these are 20 plus year old engines with really old engine control computers without knock sensors and the like.