Hello im nick from jacksonville fl i have a 98 puch korado and it was just given to me it has 300 miles it did not run at first i took the carb apart and cleaned it and it started up the only prob was that it makes a popping/backfiring type noise around the air intake so i fixed that by replacing the plug and that worked for a while but now its backfiring again and the spark plug is filthy black like its 10 years old.could this be from improper gas mix?im using a 2 cycle 50 to 1 mix. please help!