I have a 2004 Yamaha Bruin 350 4x4. It has been a great machine, and has served me well...at least until this past spring. I had it on a poker run and noticed it wasnt running quite right. There was some lag in acceleration. I didnt think too much of it until I started going up this one hill, and it just started sputtering, and acting horrible. It was like there was a "reverse limiter" on it, only I was going forward. The more throttle I gave it the worse it got. I was able to baby it to the top of the hill, and pull it aside. We drained the carb out on it, and it helped a little but not much. We figured it just had some bad gas, so I babied it to the end of the ride and once we got home we drained the tank. It ran alright for a while, but lately it has been acting up again. It will run fine, and then all of the sudden act like it has no power. I was following my dad up a hill a few weeks ago and I went to give it more gas to get over a log, and it just started sputtering around again. It wouldnt even have enough power to spin the tires or make it over the log. I had to back it down the hill, and take her home. The bad part is, it doesnt happen all the time, just every so often. THe more throttle I give it the worse it gets, and if I back out of the throttle, and then back in, it doesnt help. I am not comfortable riding it when its running like this though, because If I want to go up a hill climb or something and it does it, there is no way it will make it all the way up. If anyone has any idea what this could be, let me know.

Thanks!

 

It sounds like fuel issues .. check the rubber intake manifold iv seen the rubber crack over time causing a vacume leak resulting in intermitted problems the carb on that model has alot of parts in it remove it and just remove the bowl on the bottom you will see the main jet remove it and blow it out also remove the pilot jet it is next to the main small screw driver blow it out you should visuely see some thing wrong dirt in bowl or cracked manifold i asume you have pulled the spark plug what color is the electrode white gray // black // light tan ..?

 

Spark plug looked fine, but I replaced it anyhow.

 

I have you taken the bowl of the carb and cleaned that? I'd give that a shot...sounds like there may be some gunk in there.

 

No, I have not tried taking the bowl out yet. I will try it this weekend and see if that helps. Thanks for the input guys! IF anyone else has any ideas let me know. Thanks again.

 

I just had a similar issue with my Wolverine....it was occationally stumbling at higher RPMs. Turns out, there was some crud in the bottom of the bowl and that was hindering the main jet's ability to to suck up fuel. While you're in there, check the main jet and make sure that's not clogged.

 

Well from your pics it looks like you like to go mudding so I would check out the carb and the gas making sure there is no water and other junk in them...Clean the airfilter...make sure you have enough gas and aren't on reserve and out of gas or something dumb...and if you are cleaning the carb make sure every jet is cleanout out and you can see through them...if none of this works just message back and do you have any mods done to it if so please list and what size jets etc

 

Only other thing besides being fuel is spark. Sometimes spark can get weak, and not fire all of the fuel. Next time it acts up, remove the plug right away and check. If it is black and suity or wet, its from weak firing. If not than it is fuel. lol.

 

My buddy had a problem like that but it was constant. Wound up being a dirty air filter.

 

@CobraR6 I know it is a old post but I take a chance Did you find your problem? It was the carburator? I have the same problem with my Sportsman 800 2010