My Lawnmower must be a Chevy

My damn lawnmower never starts unless I take the fuel bowl off and clean the carburetor, and the gasket that seals the bowl is only 1 dollar!

Its actually a Craftsman with a Tecumseh 6.75 motor. I dont know whats going on in the carb. I completely drained and changed the old gas, cleaned up the bowl, cleaned up the "power screw" that has a tiny jet in the bottom and blew the fuel line clean. I dont have any sort of fuel filter on it, just a screen at the base of the fuel tank. Even if I pump the primer bulb 3X (or 10X) it rarely starts after sitting for over 3 days. Getting annoying...