today i toped out my 350rancher and when i slow down i heard a loud pop i just ignored it and like 20 minutes later the samething happend when i toped it out then i slowed down i herd a loud pop this it backfired 4 times today in a whole days of rideing. i told my friend about this and he said it was the spark plug and that it is old and need to change it my other friend said u need to ajust the valves my other friend said it was the gas

whay do u think is causeing my atv to backfire what think should i do to make it stop

 

The backfire is from a lean idle circuit. Could be a few things. Exhaust leak, partially pluged pilot jet, old gas, ethenol blended gas, or simply the mixture screw is a tad too lean.
You can verify this for yourself...next time before letting off the throttle, pull on the choke (which makes it way rich), and let off. The pop will be gone, if the issue is jetting. If it still pops, youve probably got an exhaust leak.

 

I would agree that it is probably lean, and perhaps needs a carb cleaning and adjustment of the fuel screw.

A fresh plug and a valve adjustment wouldn't hurt either!!!

 

It isn't unusual for something with a CV carb that is jetted properly under most conditions to pop a little when in an extreme compression braking situation, like suddenly chopping the throttle all the way off during a full throttle blast...

If it runs well otherwise, I might check plug color... It might be slightly lean.