After a few minutes of riding my xt500, the idle started to get erratic. First it slowed down and died. Started back up but it would rev up high without me touching the throttle, then slow down enough to where it would die if I didn't open the throttle. After it died again it took about 10 minutes of kicking to start it again, and it was doing the same thing. I drove it home keeping close attention to when it was about to die so that I could give it more juice. I let it sit for about 45 mins before trying it again and now it won't start at all, although it will backfire every now and then when I hold the decompression lever and turn the crankshaft. I'm thinking it's the carb or the timing, and not the retrofit throttle I built for my new Mikuni VM36. Any ideas on what to look for? I'm especially curious about the backfire while valves are open and I turn the crank, does that mean it's just flooded? Any comments, no matter how basic are welcome. I'm VERY green when it comes to engines and motorcycles (this is my first bike and I bought it 3 days ago) and I am just teaching myself how to be my own mechanic by using forums, websites and manuals. Thank you for any suggestions.