Guys- I'm helping out a friend who has let gasoline sit in a mower for several seasons. I changed the air filter, spark plug and put in fresh gas. It starts right up, but it sputters a lot. I suspect (should say I know) the carb needs taken apart and cleaned thoroughly.....I'm really not in the mood for this. Is there any type of gasoline additive that I can throw in the tank that will do the trick?