Seafoam works great.on a good compression motor that has been a little neglected.it will not fix the air/fuel mixture a cause of carbon build up.it will clean up the carbon but you need to fix the real problems first.last oil change i put half a bottle in the oil and the other half in my gas tank, I read the instructions I had a full tank of gas, I drove it back and forth to work I did not "get on it" while driving, after the week of driving I warmed the engine up then dropped a quart of oil out of crankcase then added a quart of ATF ran it at idle for 1/2 an hour then changed my oil and filter I also adjusted my timing and changed my plugs at this time.it runs great and you wouldn't believe some of the goopy crap in the drain pan.if your motor has good compression I see no reason NOT to use seafoam unless your motor is fresh and is clean as hell under the valve cover.mine had been neglected and was a little gunky.