I'm pretty new to these 2 stroke motorized bicycles, but have developed a passion for them, but I've been plagued with some serious vacuum leaks using or should say reusing my not carburetor My engines ran great, had 2 of them, one a straight 38 mm stroke engine, no mods, the other was a 40 mm, balanced crank pk80 type. I started experience a irregular idle then my engines wouldn't idle at all. I checked for leaks at the intake to cylinder and the carb to intake tube. I sprayed cab cleaner to detect the leak, then tried wrapping plumbers tape around the intake tube with limited success, the carb started leaking once again, checked the head gasket, jug base gasket, no leaks there. I also silicone sealed all around the carb to intake connection, but the leak prevailed. I decided that even though I had the leak sealed however briefly I still was suffering power loss. I even tried the racing carb, which seemed to have a better sealing capability, especially with the sleeve insert, but that carb leaked as well! I finally decided to pull the head and jug an discovered severe damage to the cylinder chrome coating of the cylinder. This damage was only above and below the intake and exhaust ports, slight scoring of the piston an no apparent damage to the rings. I will replace the cylinder and most likely the piston and rings as well, but Im very curious as to what caused the damage, I broke the motors in properly. Need some advice badly on how to proceed, thanks in advance!