I have ordered a new carb and kit for my riding lawn mower. The engine is surging and there is a couple things I can check . Most likely it's the varnish built up in the carb . Another is a hole in the gas tanks cap..i.e. vent hole clogged. In the mean time, w/o removing the carb, what would you use as an additive to "dissolve" this varnish build up and burn it out while running?

B12 in tank or put the fuel line in some cleaner till the carberator fills up.

Partially choke the intake with your hand if the mower stops surging and levels out while doing this then you have a restricted jet. Bypass chemical treatments and clean the carb. Some aftermarket carb are so cheap it is easier to replace them. But either way is the best route to solving this problem properly.

Just pull the float off and clean the little bullet looking thing. It gets dirty.

This stuff is amazing for an additive for carb problems.

Seafoam in every gas container for lawn equipment

Vinegar wil, clean a carb, don’t leave it soaking to long.

This is what I use also...many years owning a snapper with B/S engine with no issues

Ethanol free gas and Seafoam when you get the new carb on.

I wish I had ethanol free nearby...

Buc ees?

Both HD & the other one sell synthetic fuels for small 2 & 4 cycle engines. Use it or go through fuel problems. Word.

I have used that ethanol treatment and fuel stabilizer on my carbed motos. i use the lucas brand but I am sure others are good. As for cleaning. b12 chemtool at a high concentration in the gas and just run it, will do the trick a lot of the time.

If not many small engine carbs are cheap to rebuild and sometimes just as cheap to replace.

So if alcohol/ethanol is bad, why do so many people dump more alcohol in their gas with these additives? B12 has 20-30% methanol and Seafoam is 25% Isopropanol. The anti-oxidants in the additives are good and will stabilize fuel for a longer life. The alcohols in additives are great solvents to clean gum and varnish from gasoline. If I'm paying the $$ for that canned premium fuel I'm not adding alcohol to it.

Easy things first. Check the Air Filter. They are very important for small engines. Also look for trash in the fuel tank. Found out the hard way that the open nozzles on my plastic gas cans catch an amazing amount of sawdust, dirt, moths, and a wasp. You'll never notice the debris, and just dump it in your tank when you refill. My rider has a spider floating around in the tank now, but so far it hasn't clogged anything and I can't reach it to get it out.

I LOVE B12 for cleaning parts, but be careful using it full strength, it can melt some plastic parts, including the bowl gasket on my edger. Found out the hard way.