good to know where to start for looking for info. The carb is a marvel schebler USX series, hear they are pretty much junk. tractor runs with a slight uneven idle, occasioanl miss, then starts to load up, sooty exhaust then just seems to flood. Been sitting for a few years. is it possible hung valve? Also the intake/exhaust manifold has a crack by junction box where the 2 are bolted together.Crack Starts between 3&amp;4 exh ports and wraps down to joint of the 2 manifolds. Is there a heat rise plate in there that could be letting exhaust thru to intake? Know early 80's carbed ford 300 engines had similar setup, and there is a thin steel heat riser plate that sepeartes intake charge from exhaust, but heats up charge to prevent icing in runners.  Anyone know what i mean? possible could be burnt out because of crack.

what is cubic inch of engine?