The last few times I have gotten my M out, I have noticed white smoke coming out of the stack for the first minute or so. Not pouring out in clouds, just little puffs. If I warm it up with the lower radiator hose, the smoke is much worse. It definitely smells like coolant too. I haven't run it long or hard enough to notice if it is also burning coolant while operating.
I am assuming a bad head gasket unless someone has any other ideas.
I know none of the tractor's past history so while I'm in there I figured I could/should take care of anything else that could cause a problem later on while I already have it appart. I got a complete upper end gasket kit and a new exhaust manifold. But I've never had a Dubuque 2-cylinder opened up before and I was wondering if there was anything specific to the vertical 2-cylinder engine that I should be watching for? Other than needing its yearly changing of the spark plugs, it runs like a champ and pulls really strong.