I've used Seafoam before and find it over priced and over rated.
For carb/injector cleaner I use Chevron Techron.. The problem with a motor that isn't brought up to max heat periodically isn't just carb gum but deposits on the valves and stems. If the valves aren't working freely, it's not going to start and if it does it's not going to run smooth. The gas is always blamed. It's not always the gas. My 1986 Jeep, 50,000 miles taught me this problem. It didn't want to start, backfired, missed, etc. I used Marvel Mystery Oil in the oil and gas and it now runs smooth.. I know, it sounds like snake oil but it's been around for at least, my knowledge, 60 years. It frees lifters and valve steams of oil sludge and carbon.. It takes maybe a tank of gas with the crank case oil added but it works, at least for me. No, I don't sell the stuff... In my experience....