took off carb to get it clean i had goine through some mud and some was in the bowl and the top of the card but it still ran then i put everything back in all the same and now i have this problem??

 

I did not look at my KQ400, and I'm not sure if it has a constant velocity carb, but I'm wondering--is there a vacuum line connecting to the carb?
A missing vacuum line/connection can cause the problems you are experiencing.

 

yes there is a vacum hose that runs from the fuel petcock to the top of carb then another that runs from the side of carb to under the seat ......

 

I am having the same problem. It is as if the reverse rev limiter is kicking in all the time. It seems to rev out somewhat fine in neutral, but under acceleration it is sluggish and cuts out around 10-15 mph. Have you found a solution?

 

Mrbocifus --Try jacking up the back end and see if it still cuts out with it in gear. If not then it should not be limiter or any clutch problem. Maybe valves- if done only under load??
If it runs fine in neutral I would not think it would be a fuel/air mixture problem.
Just something to try/think about.

Phil, could your float be stuck down, not enough fuel for main jet? If it will not go past 3/4 throttle it is a main jet problem or lack of air? try with air box lid off, is choke stuck on some? Maybe the top bellows for main jet is not seated completly or tear in rubber?

 

figured it out .. it was the darn petcock now i just run it on reserve cause the ON is all jacked up and yes the float was off a little which was my problem when it hit full throttle where it was cuting out