Have a 1999 Grizzly that is sputtering at full throttle,it idles and accelerates good but breaks up at full throttle. Anybody have any ideas.

 

Have you checked your plug, How does it look?
Any carbon build up?

 

Your carb is dirty,have it cleaned and it will work good again.This is A common problem with Yamahas due to their poor air cleaner design.

 

wgr,

I have had similar trouble the last two wekends with my '00 Grizzly. Mine got so bad, it would only go 10 mph, and popped like 4th of July fireworks. I thought I had taken on water and maybe dirt through the airbox, but it checked out clean. My spark plug was fouled a little, but didn't fix it. It turns out I broke a rule and bought the last tank of gas from a local station known for bad gas. I drained the tank, refilled, problem solved....so I thought. I drove it on level ground for a very short distance, seemed fine. It sat for a week. By the next weekend, the same thing happened. This time, I realized that for the previous draining the fuel valve was set to "on". This left the reserve amount in the tank. The reserve portion is the lowest point, and that is where the water will settle. Second draining, put valve in "RES", and put the first amount into a clear 2 liter bottle, plenty of water was visible in the bottom. I also disconnected the fuel line between the valve and the carburetor, and flushed with Gumout carb cleaner until it ran out the drain hose. I then reconnected, flushed with gas. It fired up and has ran perfect for 10 miles. I took it down by the river to test it out under trail conditions. This may not be your problem, but it appears a very small amount of water can quickly bring down a might Grizzly (as it would most any ATV)

Hope this might help.

Yammer_Hummer

 

I think your on to something here Yammer_hummer

That sounds kinda like what that noise I have been hearing. light ping, & a poping noise ocasionally comming from the back of the pipe. And I was running on res.

Hey, What grade/octane do most of you guys run? Maybe thats part of my problem too. My first tank of gas was mild/premium grade 89+ octane and it ran real good, however my second tank was low grade 87octane from this old country gas station.

Would I see more performance and better engine life if I ran the really good stuff the 91 or 92+

That doesn't burn too hot for this motor does it?