I am trying to get my grandfathers 1941 John Deere B back up and running. I have put a rebuilt carburetor on it, had the magneto rebuilt, put new plugs in, changed the oil, put all new fuel in, and managed to get it started. This is still an old hand crank style. The problem I am having is people are telling me the tractor should run at a solid RPM. The tractor seems to ramp up and down almost as if it is firing to ramp up then missing a few times then firing again. The tractor doesn't die and moving the throttle will make the engine RPM's increase and decrease however it won't stay at a steady rate. Any words of wisdom? This really has me frustrated at this point.