Got back from the trac last weekend and sprayed off the bike and put it up. I had to go out of town for a week and couldnt get to it until today. I cleaned the air filter, put on a pro taper throttle tube and new grips and then tried to crank up the bike so I could chage the oil out. It took alot of kicks to get it going but it cut off after a minute or so. I finally got it cranked up again and took it up and down the street a couple of times and it was backfiring like crazy on deacceleration. When I slowed down to an idle it just cut off. Now i cant even it get started. I put a new spark plug in and the old one was a bit black and sooty. Any suggestions???