I was a McCuloch dealer --factory service center in the 1970 -1980 . Best thing to do is tear completly down , install new seals -- clean and seal crankcase --- my experance has been crankcase may have air leaks . After resealing pressure test , this will save a lot of time later . Repair kit in carb , solid state ignition module , new fuel felter -- or clean old filter , a couple drops of water will plug a fuel filter .
You should be able to tear down , repair , put together 1 time and have a good runing saw . This usually works , sometimes not , good luck .
Rog