Ok this thing is driving me nuts. I have replaced the nasty air filter, new diaphragm and gasket kit with fuel screen for the carb. The thing will run like a champ for about 35 to 40 secs. And then shut off. I double checked plug gap. Pulled plug after shut down to see if its getting soaked as the exhaust has some smoke from it. Nothing noticeable.

I am at a loss at this point. HELP!!

Its got a fuel restriction someplace. Double check your work and make sure the fuel strainer in the tank doesn't have a lot of crud and everything downstream from it is clean and clear... particularly the needle valve.

I agree, remove the bowl and actuate the float by raising it and lowering it. Fuel should dump when the bowl is down

Ok... Remember now this is a small push mower with a standard B&S motor, bulb primer type carb on it...

~Rechecked the gasket for the carb to the tank- good
~blew air (canned air, PC cleaner type) through all ports and screens to check for any possible blockages - none found, or if there was.. . it was unknowingly shot out.
~Looked through the fuel port into motor and found nothing out of the ordinary.
~ Carefully re installed everything and got the same. Run like a champ and then dead after a hot second.
~Another evening of fighting mosquitoes and no result for my efforts. It's starting to become a good candidate for a target at the firing range.

PS thanks for any advise y'all give.