Outdoor Power Equipment and Small Engines - Carb trouble

Hi all,
I bought a Craftsman all wheel steer lawn mower this weekend.
Got it cheap, so theres always a catch. Someone has put a different carb on it. It has a primer bulb like you would find on a push mower. It has the linkage, so it came with a different carb from the factory. It has a Briggs 12.5 hp engine.
As long as I push the bulb primer, it will run. My question is, is this carb. not big enough for this mower or could the carb just need cleaned?

Thank you

Please post tractor number and engine number

Tractor model number is 536.255860. The engine number is 143.436092 Ser# 3074D. Those are the only numbers I found on the engine.
Thanks

That's a tecumseh engine, and it sounds to me like someone managed to put a push mower carb on a riding mower engine???! Forget about trying to make that work...sounds like you're going to need a donor engine for parts. Who knows what else is messed up if someone went and did something like that...

Carb#632774 Sears price $86.39. Tractor looks like it would be worth the carb price.