02'Sportsman 500 will not start!! When I try to start it , it will turn over fine, and I know for sure that it's getting fuel!! I pulled the plug and replaced it ! When I was checking for fire I noticed that It was not getting any fire untill right when I turn the ignition switch to the off postion and then It fired one time!(one spark) So I put the plug back in and tried to start it a few times and twice when I turned the key to the off position it back fired hard!! What could it be?? Thanks!!

 

u could have a pinched plug wire or a bad connection could be the coil

 

A "coil" is actually 2 individual coils of wire, 1 inside of the other. The outer coil is activated with 12 volts. When the outer coil is deprived of the 12 volts (either positive or negative ), the amperage is amplified through induction into the center coil. The center coil is attached to the sparkplug wire.

On older cars, when you turn the key on, a positive 12 volts is <u>continually</u> supplied to one of the small terminals of the coil. The other small terminal goes to the points in the distributer. These points make and break a connection to ground, thus collapsing the outer coil and producing a spark.

IMHO, this would suggest to me that there is a problem with whatever triggers the coil (or even wiring that carries this signal).

It sounds like there is voltage going to the coil, or there wouldn't be any spark at all. When you turn the key off, you collapse the voltage flow of the coil, producing a spark.

To be politically correct, a backfire is actually an explosion that fires BACKWARDS from the compression chamber, and out through the carb. In your situation, you are experiencing an afterfire. This is caused by excessive fuel in the exhaust system that was ignited by the single spark from when you turn the key off. (As you stated "and I know for sure that it's getting fuel!!")

I hope that I wasn't too long winded, but the better that a person knows how a system works, the easier that it is to find the problem.