Old trick we used in the 1960's and 70's. Start up the engine and let it warm up a little, slowly pour about a cup of transmission fluid down the carb. You will see smoke come out the back, shut engine off quickly and let set for about 20-30 minutes. Restart engine and rev it up a little, hitting the pedal a few times until the exhaust clears up. It has cleared a lot of carboned up engines back in the day when lead was in the fuel plugging the cylinder heads. I've seen chunks of carbon blow out, back in the day.