I have used it 2/3 Sea-Foam 1/3 gas. Have put full can to less than 1/4 tank. Helps with really cruddy carbs. Using full strength makes for hard restarting and could foul plug. Or throw a can of BerryMan's Chem Tech into 1/2 tank or so if carbs really need a good cleaning. Stronger than Sea-Foam but not as gentle on non metal parts. Can be used occasionally without harming anything.