I had exactly the same problem, I tried to clean the carb several times without any luck. I gave up on the carb as it was an EPA style without adjustable mixture needles. Bought a new carb for it, installed it and the engine fired up right away. Took me 10min to let it warm up and dial the mixture, it has been fine ever since.

I recommend to buy the replecement carb old-new stock mfg pn: 632334A Tecumseh Carburetor with mixture needles

This place helped me out with one.

First off ,how old is the gas????? If it sat over the summer, meaning almost a year with gas in it. You will need to rebuild the carb or buy another. If you want to save some dough and like to tinker, rebuilding is the way to go. Just go out and buy some chem-dip at your local auto parts store and a rebuild kit for the carb at the local small engine shop or whatever place you can find. Tear the carb down, place all the metal parts including the carb in the basket "excluding the plastic and rubber parts" and let them soak for 2-3 days. Then you rinse all the parts including the carb with warm water and use high compressed air though all the orifices to dry the carb and parts off. Then re-assemble, It's really easy and it saves you money, not to mention, it's self gratifieing that you did something yourself and it works!!!!!!!!!

You may need to clean the carb or possibly put in a rebuild kit, also how old is the fuel? Old fuel will also cause it to run bad ( old fuel meaning more than 30 days old), they say the fuel we use today has a shelf life of about 14 day's then it starts to go bad.

Tankfilter first sludge can be on the bottom inside the tank a canister cleanup engine cleaner Tecflow or an other brand of fuel (engine) cleaner second is to clean the filter of the fuel-tap and the thirth step is the float chamber and the nozzle inside the carburetor and the last step control the gaskets and airfilter thats in most cases enough the little channels for idle speed could be clogged in the carburetor then spray it for a day or 2 with a good startcleaner or help it on the move with an engine starter spray ,but one time only if all the parts are controlled always its good to control the movement and the of the pushrods and also the oil level ,oil monitoring for ignition and also the colour of the spark of the sparkplug. thats normally the way , but in this case because it runs good and after a while there is arisen a problem i read after a good functional engine what i am thinking on possible loose of compression by mechanical compression release or gasket overheat by run out of oil the oil level control is having a protection ? its also a suggestion in that case

Check all the adjustments for the motor to drive wheel engagement from your handle. I think you will find that you are starting with the wheels engaged. You handle is not disengaged. As a test only, turn the wheel speed lever down to the very lowest setting and then start. If it does start be careful because if the wheel speed is set too high the blower will operate but the drive wheels will not disengage after you release the handle and there is no brake . You will only be able too stop it by shutting off or reducing the motor rpm. This is a dangerous situation.