I've used Seafoam for nearly 6-8 years, with good results. My 2, '88 Wheel Horse 310-8's with Kohler engines have a check valve in the carb, to prevent drain back to the tank, if left setting for a few days. Ethanol laced fuel will cause that check valve to get gunked up, and let fuel run back to the tank, and takes a while to pull fuel back to the carb. Per directions, I pulled the fuel line from the carb, and put a short section on, poured some in full strength. Let it set overnight, then put the line back on. Put prescribed amount in the tank, and mowed for 4 hours. A week later, when starting up to mow, it fired right up. After that, just added the prescribed amount, and both start fine.
I now use Stabil 360, which stabilizes fuel, and also cleans the fuel system. It only takes 1 oz. per 5 gallons of gas, so add it to my fuel cans, before filling them up, so I know it's in there, and mixed up. I still use Seafoam occasionally on new to me tractors. Seems I'm always picking up an occasional garden tractor, both 2 wheel, and 4 wheel. If they are runners, I'll add it. If non- runners, I'll clean the fuel system, then add it to do a final clean-up, even using the gas with Stabil 360 added.