The carb can look clean and not be. The first thing I would check is the main jet. It's either an adjustable jet or one that looks like a hex bolt in the bottom of the carb. See the pictures to check and clean.

From time to time the question is asked about why an engine will not run long, or smoothly, or will start with starting fluid and not continue to run. 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 3 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 the center-bottom hole.

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Rolm: You may wish to start with a simple Fuel Treatment Concentrated Carb Cleaner Usage (2 ounces) with fresh fuel . Also I sometimes spray a little carb cleaner within the Venturi to start the cleaning process. If a 1/4 tank does not resolve your problem then , follow Bays advice and goe further into the Carbs Fuel Circuits with a visual and more thorough cleaning .

Does the unit have a fuel filter?
IF so, it may be restricted to the point that the engine will run fine when not loaded, but as soon as it needs more fuel, the filter won't allow enough flow.

Thanks for the info. I did clean the carb once again I did Add hi-test fuel with carb cleaner. Just waiting for a snow fall to test.

rolm: Bill also made a very valid point . Chck your fuel filter also , I always do but sometime neglect to mention the obvious to Old Wise Mechanically inclined Dudes such as you . The cleaning action of the fuel treatment will start a slow dissolving action even as we converse . Good Luck , heck must be nice I have already blown snow for at least the last 3 weeks every second or third day lol ...E

Heh heh last December, I struggled with 2 cripples to get the drive way cleared. 3 cripples actually, I was still doing chemo. Any way, I did some parts shifting and bought a belt or 2 and had 2 runners going into last winter. As a result of my careful planning, (luck) I dint get any more blowable snow. Even though it is in the 20s right now, the next precip is expected to be rain. Thus begins the dance.

Andy: Sorry to hear about the Chemo , my Sister just went through it and has been given a clean bill of health . I hope the same has been you reward. Also just to make you feel even better , it's still snowing up North here lol . After todays Snowblowing I have a Rad Thermostat to change out , the heats getting a little sluggish , all the Best Dude !

Dont be sorry, It was caught early and absolutely stomped. Like your sister, I am mending well. Recent blood work gave me good news.

Ahh...Great Stuff Andy ! All the Best to You and Yours this Xmas Season Bro :).