I have a 2002 Yamaha Kodiak 400 that I just started having problems with.  Last Saturday, I had about 1/4 tank of gas left so I filled it up.  About one hour later I went to take it for a ride and it would not fire.  This machine has always run great for me, and I had just used it the night before.  After cranking it over a little bit, I tried shooting a little starting fluid in the air box but that did not help at all.  So I let it sit for the day and went back to try again that night and it fired up.  It ran rough but it ran.  I took it down the road and tried to clean it out and it started to run great.  I thought that it just was bad gas or a little dirt in the carburetor.  So I brought it back home and went to use it Sunday and it did it again?  My next thought was water in the gas, so I drained the entire tank and carburetor out.  Filled it up with fresh gas and a little isopropyl alcohol, thinking that would do it.  After letting it sit like that over night, I tried to fire it again, but it still won’t go.  I tried to shoot a little ether in the spark plug hole this time and still nothing.  So now I think it is electrical, but not sure what to look for.  I am going to check resistance in the plug wire, and look over all the connections, but are there any other ideas out there?  I appreciate any help from you guys.  Thanks!!!  

Pull plug and let it set against motor turn over to see if you got spark. If not then would suspect problem in charging system. Powersports has a pretty good parts break down, may be able to look it over to get an idal where to go from there. If you are getting spark maybe carb. I've own several Yamaha bikes over the years and they all are cold natured. Full chock no throttle and hit the starter. Easy to flood. Good Luck  

if you are still looking for anwers to this, i would suggest buying a new spark plug.
i have had spark plugs upon testing show a good blue spark, then when you put them in the engine they don't work so well.

I bored and rebuilt a project yamaha blaster that had me scratching my head for 5 hours.
I put it back together cranked it up and it ran awesome for 5 minutes, then it started running rough, spitting and sputtering. I checked the spark plug, it had a good healthy blue spark but the ceramic was loose from the steel nut area, and when I put it back into the head it was firing against the head. so only a very weak spark was getting into the cylinder.

took me a bit to figure it out.
long story short i spent forever checking it out and then the last thing i tried was putting another plug in it.  it fired up and still runs great today!!!  

2000 Yamaha Grizzly 600 No spark.
Replaced colil & cdi box.
No Spark  

check the stator behind the magneto.  

check the stator behind the magneto.

it should be on the left side of the engine under the side cover.  

wolf1:
check the stator behind the magneto.

it should be on the left side of the engine under the side cover.

Hey wolf1, or anyone else, would you happen to know how to check the stator on a 2000 Grizzly 600?  

I have the same problem with my 00 grizzly 600.i replaced the stator assembly and the cdi box still no spark.dont know what else to do.please help.