Does a four wheeler have a way to time it Mine won't start and keeps backfiring through the carburetor?

most likely no. especially if it is a 1 cylinder. just like a lawnmower, the camshaft is built into the same peice as the crankshaft. you can't advance or retard the timing. i am most certain that your problem is in your carberuator. It is probably dumping too much gas into the cylinder. when the piston comes up and makes compression, the spark plug ignites and causes combustion, the exhaust valve opens and closes quickly, but there is so much gas in the cylinder that when the intake valve opens again to let more fuel in, the fuel already in the cylinder is still combusting and causes a backfire on the intake side which also burns all the fuel back up to the carberuator in a quick flash and backfire. i bet the spark plug is either fouled out, or showing signs of overheating from getting too hot because of prolonged combustion. tune up time.