After 2 days now cleaning and double checking everything with the carb on my recent buy, I've decided the bike must have the cdi going out. I cleaned the fuel system thorough yesterday and it fired up but wouldn't idle without poping and skipping . Once throttle was rolled on it ran great. This morning went 2 miles to get gas and it didn't want to start but finally it did and it ran the same till 1/2mile from home, then suddenly bogged and popped, backfired, wouldn't rev and wanted to die, till it did. The motor sounded like it was working hard. Spark plug was really light grey and dry. Went back through the carbs and boots, triple checked for any air leak ect.. Got it back together and it started up ran smooth, idled no popping for about 2 minutes, then bog and backfire, then die. With full choke I can get it to start after five or ten minutes but won't run. Which parts are the most likely culprits on these bikes, I haven't done much with the Yamaha's in a while.