I picked up an older Stihl 026 "red master control switch" in really nice condition. Compression is good and the cylinder and piston look to be in very good condition. After starting it, it takes a few seconds to go to idle and at full throttle, it seems to be dieseling. Adjusting the carburetor or rather trying to fine tune it isn't giving the results I would hope to get. I'm thinking air leak but I can see that the carburetor looks to be after market and the air filter definitely is. Any suggestions before I start spending money and my time?