to20 won't run

I am getting desperate. I have a TO20 that will start on starting fluid, but won't run on gas. I have checked everything I can. It has fire, good compression, is in time. Runs great on starting fluid. Someone has had the carb apart before I got it. I think they did something wrong, I don't know what.

You have three filters on the tractor. Start with the easiest and go up. First, lets eliminate your gas flow problem. Pull that bolt looking thing out of the bottom of the carb. Turn on the gas above and the flow is suppose to look like a "cow pithin' on a flat rock". Yes? Uh oh, you got internal problems. No? Didn't think so.
Turn off that gas flow and look at that cute brass fitting on the carb. Pull it out gently. Inside that you will find a screen. Pull it out and clean it. Compressed air works good. No compressed air? Carb cleaner / brake clean works also. Put it together and try that gas flow again. Next filter above that is in the glass bowl under the gas tank. Pull it out and clean that flat screen and fuel bowl at the same time. Before you take it apart, get yourself another glass bowl gasket to replace it with.
Last chance is the filter inside the tank. That is the stand pipe on top of the fuel shut off valve. If that is plugged, your probably going to better off with another valve assembly. I cleaned mine up with a lot of time and luck. Now if your filters are clean, your choices are basically down to a float stuck shut or the carb screws turned in or out too far. Check those filters first as the carby has been done.

I have gas flow to the carb. The float bowl is about half full of gas. I think is in the carb. I need to find one off of a running tractor to try it. I have tried the adjusting screws with no results.

Have you checked for a strong spark? It should be fat and bluish-white, the color of lightning. Don"t assume it"s the carburetor! To start and run, it takes a strong spark at the correct time to ignite the correct fuel/air ratio. The carb is one leg of that three legged stool. Timing and a hot spark are the other two legs. More often then not, the spark is the problem, but assume nothing and check "em all!

A simple test is to remove the air filter hose from the air horn of the carb, hold your hand tightly over the opening and give it a crank.

You should get good suction, and have gas on your hand and dripping from the carb.

If no suction, something is wrong, as in valve timing, stuck valves,or major vacuum leak.

If there is vacuum, and no gas, the main jet is clogged or not enough fuel in the bowl.

Don't be afraid of the carb, it is simple and field serviceable. Take it off, work over a clear, uncluttered surface so dropped parts can be found.

Ease the bowl off, look at the main jet. It is probably clogged. Clean, clean, clean! Ethanol gas is notorious for leaving deposits inside the jets. Poke them out with a small wire, spray with carb cleaner. If you save the gasket, and nothing is worn, it will go back without a kit.

When you out it back on, before connecting the fuel line, open the fuel valve and let some gas flush the line. Carefully connect it to keep any debris out.

Thanks guys, I'll give it another try in a few days.

I have spent a few years pulling on wrenches and until you check the basics, your wasting your time and money.
As your machine starts on fluid, chances are pretty good you have compression, timing and spark.
Your missing the gas element. Like I said, check the filters. Beyond that is the float level which can be checked externally by pulling the bottom plug, install nipple, 2 foot of clear hose and hold the end of the hose up to the sky. Turn on the gas and the fluid will flow into the hose and show you the level inside the carb. If your only 1/2 full, the float level is not getting enough gas into the carb.
Best of luck!

stop using the starting fluid or you will have nothing left

Just because the float bowl is full does NOT mean you have good flow to the carb. It can be full but still not flowing with enough volume to maintain the proper flow in the carb.