Hello,
I just bought a 2005 kfx400. It is starting to backfire and is hard to start up now. Every time I give it gas it backfires bad and shuts off. When it is running and I give it gas it will start to die then kick back up .What could be the problem? Any help at all would be appreciated.
Thanks

 

After doing alot of research on these, it sounds like the timing chain needs adjusted. These things take a good bit of maintenance if I am reading all of my research correctly...

 

It could be your timing chain but I would say it sounds more like your valves need adjusted I had a 2004 KFX 400 and I actually had to replace the timing chain and the valves. If you here a ticking noise while it is running it could be the timing chain but if its just hard to start and back firing I would say its the valves. When replacing mine I found the parts cheapest at this place.ATV Parts, ATV Tires, Dirt Bike Parts & Motocross Gear | Rocky Mountain ATV/MC

 

This happened to me also turned out that i had to get the vavles done and also my timing chain was streched and needed a new timing chain tensioner

 

I can't tell you how many posts you will see about backfiring in an ATV. They are everywhere!!!!! I have a 2000 Suzuki Quadrunner 500 4x4 that does the same thing. I researched this forever on forums until I found a guy who knew what was going on......

When my ATV does this, it is time to buy a new battery. I tried everything.....new plug, drained the gas, put STABIL in my gas.....nothing worked. I finally noticed in a lot of these threads that people will mention that they are hand cranking the ATV.....Duh!!!!
Bad battery. My ATV will do this until I put in a new battery and it cures it every time.
It is good to disconnect the battery during long periods of no use and charge it before using it again. Try this......it works for me!!!!

 

Did you try adding some gas additive? mine was back firing too. I have a prairie 700 2004. I'm not sure where i seen it, but i was watching something about the effects of ethanol, and what it does to the carburetors .After 30 days it actually separates itself from the gas and really does alot of damage to the carburetors. I added some Sea Foam to my gas tank and my quad runs much better and no more back firing! Before you go ripping it apart, i would suggest that you try this! Aslo lucas oil makes a fine additive for this too! good luck