I have a 05 ozark that has a lot of top end chattering at high rpm. It only does it when u are running over 30 mph on the highway, and gets worse when u go up a small hill. It is broke in, (50 hours or so) and the valves have been adjusted. The atv has done this since new and the dealer said at high speed they will have some noise. Sometimes it sounds like the valve or chain or something is gonna come thru the gas tank. What the heck is wrong with my ozark. Also this noise will only appear when u are going fast no matter how much or little gas u give long as its going fast on the highway or gravel road, u can rev it sitting still or going slow and it wont do it. Help

 

put 93 octane in it and the noise is now hardly noticeable, any thoughts?

 

Was the other gas old?
How does the spark plug look? Does it show signs of detanation?
I cant believe the motor was pinging that bad, and still survive. But its posible you had some very low octane gas in there. If higher octane works, then thats the fix.

 

No the other gas was new i usually go thru a tank every cuple of weeks. As for the plug the metal tip is a light grey bronish color, and the white insulator is totally white. I don't really know what the signs of detination are. I do think it really odd that a 250 need high octane, but it did make it a lot better even though I still hear it when going up a hill on the highway.

 

Heres an article on reading spark plugs, and how to look for signs of detonation.
http://www.dragstuff.com/techarticle...ark-plugs.html,
Its posible that the carb may have some plugged passages, and the main circuit may be a bit on the lean side, which can cause detonation.
Next time its making the noise, slowly pull the choke on, this will enrichen the mixture, and see if the noise goes away. If it quiets down, then id take the carb apart and make sure the main circuit is clear and increase the main jet one size.