since you get the same result with either carb, i'd look at a few things.
i would do a compression test first. you need to have 120 lbs or higher to run correctly.
i would also clean the exhaust out. a plugged exhaust will cause a flooding like situation.
i would also make sure you have the correct spark plug with the correct heat range for your engine. too cold of a heat range will acvt as if the engine is flooding too.
if all these things are in order, and the engine still acts funny, then i would check fuel flow, and make sure you dont have an air leak. you can drop the exhaust and look up thru the exhaust port. while looking in the port, roll the engine over slowly and look at the piston side wall. any scrapes or smear marks are a good indicator of a lean situation caused by an air leak or lack of fuel in the mix or lack of oil. these scrapes will lower compression and make the engine seem to act as if its flooding.
once you get the engine to run and stay running, then do a plug chop to determine if the carb you are using has the correct main jet.