I got a 1980 qt50 a couple months ago, didn't run when I got it, so I drained the gas, cleaned the carb, new plugs, pretty thorough tuneup overall and got it running. It ran good, but I rode it the other day and at the end of the ride it didn't want to idle and was kind of gutless, and would not run without throttle. Now it won't start at all. I did the oil pump block off conversion and am mixing my gas at 40:1 with no problem until this. I have good spark and can smell gas on the plug. I noticed that the inside of my gas tank is fairly dirty, so I tied the oil tank in as reserve and tried running out of that and still nothing, it almost sounds like no spark, but the spark is great. Any advice would be appreciated, I'm a little stumped here.