I am a believer at least for small engines. I had a chainsaw and a weedwacker that were so hard to start that you would have to stop and rest your arm. A landscaper convinced me to try Seafoam. I had low confidence in any type of "mechanic in a can" But Wow, both of these start with one or two pulls like they are supposed to. I have been keeping a couple cans on the shelf for years since then.