Clean the hole in the carburetor Main Jet.

The problem is usually because of a blocked or constricted jet. The small ones are easy to miss.
Shown are 3 of the typical jets and the small holes. All 4 are Tecumseh jets. Briggs jets are similar with the center-bottom hole and one on the side. All these holes need to be fully clean and open for the engine to run correctly.
Some jets only have a small hole in the side as the old style Tecumseh jet shown.

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Those clogged little holes have made a ton of cash for lawn mower fixers! A thin wire poked thru them and a quick "puff" of air from yer mouth does wonders!
Rusty Jones

Thanks for info . That worked really well , it runs now without the choke on all the time . Now I need to know how to adjust the jets so it runs smoother . thanks again

A couple things-
Your fuel may be somewhat suspect and the engine won't run smooth no matter what you do until it has "fresh" fuel-

Basically, adjusting the Main jet goes something like this-
With the engine at high speed, slowly screw it in until the engine starts to "drop off".
Note position and screw the other way until drop off.
Split the difference.

That said, that works great when the engine is revving away under no load.
In reality, you probably have to back it out SLIGHTLY to get max power UNDER LOAD. That's where the "rubber meets the road".

In addition to that, I'll adjust the main jet first and then take it down to idle. Quickly rev up to full speed. If it stumbles, slightly adjust the idle air screw in or out until it revs up smoothly without hesitation or stumbling. Most carbs today don't have these two adjustment screws.

Sorry for my ignorance but is the main jet on the bottom of the bowl and the idle air screw on side near the top ?? thanks

Yep

17.5 hp Tecumseh will only run on choke. I installed a new carb. Still only runs on choke and sometime backfires thru the carb

Getting good fuel flow to carb? fuel gravity feed or fuel pump? Has flywheel been disturbed? Engine ever run low on oil?