Charles H.
Lean fuel mixtures can cause it to run hot, but so can retarded timing, as the fuel will still be burning when the exhaust valve opens. Adjust your main jet by closing it up all the way, then backing it out between 2 and 2 1/2 turns. Use this as a starting point. Turn the screw on the main jet in until the engine starts to "lean out", then back it out until it starts to run too rich, then run it back in a bit.
Check and adjust your point gap (maximum opening should be about .020"). This should get you pretty close. If you have a timing light there is a mark on the flywheel that will be visible through the hole on the right side of the blower housing, but often that mark is very difficult to see. I'll run the engine about 2/3 speed and go back and forth a couple of times between the carburetor main jet and the points to find the sweet spot, where the engine seems to strain the least to maintain a certain RPM, and still respond crisply when the throttle is opened.
If after this, you are still having trouble, make sure the points assembly is ok. A cracked piece of bakelite on the points on my 129 drove me crazy trying to keep the points adjusted earlier this summer, replacing the bad points made all the difference.
If you can't get the carb to run rich, then it's time to pull it off and clean it out because you probably have a partially clogged jet.