onan carb

I have a wh?elhorse 520H with the onan performer 20 hp that has carb issues. It had set for sometime before I got it. Carb was full of oxidation on the aluminum and I cleaned it best I could. It will usually run great for about 2 weeks, then carb will mess up and flood again. I have cleaned it two more times, and checked all passages. Everytime I take it apart, the oxidation is there again. I have drained and cleaned tank, new fuel line and new filter, so no trash, but about every two weeks I am at again. What am I missing and how do I keep it from messing up. May be looking for another carb if anyone has one.

That carb needs a good 24 or so hour soak in a good carb cleaner. Then you need to use something like a Dremil tool or such to polish up the insides. Then maybe run say a quart of ATF in 3-5 gal of gas and run it in it which will help clean it up even more and also help the engine in general

Eagle One All Wheel and Tire Cleaner.

Are you using gas with ethanol blended In? I have had similar problems with a corrosive film forming inside the carb using an ethanol/gasoline blend. This is caused in a vented fuel system when moist air is drawn in to the fuel tank. As the temperature changes over time, water condenses out of the air and is chemically attracted to the ethanol, which forms a weak acid. The metal alloy used in carbs typically contains zinc. Zinc is one of the lowest metals on the metal nobility range. It will readily sacrifice ions in a reaction with other metals and chemicals. With the formation of the weak acidic solution in the gas tank and carb, the zinc loses ions to the acid solution. In my experience rebuilding small engine carbs which saw ethanol gasoline, there is a white sticky paste (Zinc oxide?) in the fuel bowl and internal passages. If the corrosion goes on for a long time, there will be pockmarks and perforations throughout the carb body. Time to replace the the carb if that has happened. If the carb can be cleaned up, and the engine will run properly, you can prevent the problem by using pure gasoline, preferably pretreated with Stabil or other good fuel stabilizer. I had to replace several small engine carbs and one on a partner cut off saw, costing several hundred dollars in all. Since switching to non-ethanol gasoline, I have not had another problem.

And I'll add use ethanol free fuel (if available) treat with Stabil or other fuel treatments that will hep counter fuel degradation and maybe offer some protection for the rest of the fuel system. One of the few fuel treatments that's not poo-pooed on this site is Sea Foam, I might consider trying that too, it did wonders for my Wheel Horse and straightened out some of the fuel system problems on an old Cub Cadet I play with.

I run Mobil premium in all my mowers chainsaws
trimmers ect. The detergents in the gas keep fuel system clean, and the 2 cycle mix I use has Stabil blended in it so no worry when they sit unused for months

Carb came out of soak, polished and cleaned insides as suggested, put together with all new gaskets, fired it up and runs great so far. I put fresh 100% gas in it along with some atf. We will see in a day or two, because that is usually how long it takes to mess up. Once again when I took it apart, it had water in it and where it comes from, I have no idea. Hood is on, breather on, and no open place for water to get in. Now has new fuel line, new filter, and new cap on tank just in case. We shall see!

I use 87 octane ethanol gas in everything from 2 cycle string trimmers to an old gasoline powered semi tractor with never a fuel issue with any of them. It's amazing what ethanol gets blamed for these days.