Oh, forgot.

Latest technology for those old engines....
Buy a "crock pot", or "slow cooker". Essentially a ceramic covered pot with a heating element for slow cooking food.
Buy a jug of "antifreeze" used in cars. Not the "Earth friendly" stuff, the real stuff.

Remove the "O" ring of the carb and the backplate and head of the engine, and submere it in antifreeze in the cooker. Use low heat overnight, then warm water and a toothbrush the next day. With an engine that old, you may need to dis-assemble a bit further, but this will get the engine back to "nearly new" condition.

Oh, and of course, NEVER use the pot for cooking food after. The ceramic will absorb some antifreeze, which is extremely toxic!
Dennis-