Here is another vote for Seafoam. I use the stuff for everything, including my car because I am forced to buy unleaded gas with 10% or 15% ethanol in it. What the others have said about moisture is dead right. Ethanol is notorious for not only bringing moisture with it, but also causing condensation in fuel tanks that see hot and cool temps.
I put Seafoam in every can of gasoline I buy. I use it straight out of the can to help clean a carb that is running a little rough. I'll start he engine with no air filter. Then I'll pour a little Seafoam in the carb at a time. It'll blow big clouds of white smoke which is normal. After 4 or 5 times of pouring just a dab of Seafoam in, I'll pour it freely until the engines stalls. I let it set for a period of time. The length I let it set is dependent on how poorly the engine was running. It's usually just a few hours, but I have let it set overnight. It's amazing how many times doing just that will smooth a carb out. The problem is usually a build up of moisture laden ethanol fuel and sometimes a touch of varnish.
I also use Seafoam to prep all my engines for winter. I'll fire the engine up and let it get warm. I then do the carb trick just like trying to smooth out a sluggish carb. Once the engine has been stalled by the free pouring of Seafoam, I'll remove the plug and shoot a healthy dose of Seafoam spray into the cylinder. Then, I put them away for the year. Come spring, a couple of pulls and I'll get quite a bit of white smoke, but it'll fire and run without all the cranking on the engine. I have never had to replace a carb on any piece of my OPE in a whole lot of years.
Now, that's the opinion of a small time operator that has simply picked up tips and tricks from old time mechanics. Below is a link to a page on Seafoam's site with detailed instructions on how to do a LOT of things with Seafoam. Some of it is common sense stuff, but there is some very useful info on there too. I have every one of the How 2 files downloaded to my local hard drive for reference. And, before anybody asks, I have no affiliation with Seafoam at all. I'm just a long time, satisfied user. Hope you can find something useful on the link.
I do have to say that I just got home from scrounging through a guy's shed full of small engine stuff. He was in business a LONG time and was an Oregon dealer and had also received the Kohler Gold Certification. He died suddenly and his cousin is selling everything out. I bought two, 24 bottle cases of Seafoam for $5 a can. He had 10 or 12 more cases, but would only sell me 2 cases at that price. I couldn't refuse. A single can of Seafoam at my local O'Reilly store is $11.49. I bought a lot of other stuff as well, like a 24 count case of Champion RC12YC plugs. Right now they are $4.99 at my local O'Reilly store. I gave $1 each for them. Couldn't pass that either. LOL!
Here is the link:
https://seafoamworks.com/how2instructions/
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