The quad is running fine for the most part, but it does not have full power in the mid-range around 4000 rpm. Appears to have good power below and above the mid-range.
Almost feels like when you are going backwards without pressing the yellow override button. Like it is missing...

Have changed the sparkplug without any results. Any suggestions?

THANKS,
Johannes

 

What did the spark plug look like?? Was it black or light in color??

 

Not really black, but dark brown. Thought it was looking good.
Johannes

 

4000 rpm on on 4 stroke, could you be on the rev limiter?
I don't look at the pod when i ride so I don't keep track of the red line.
Could be a dirty air cleaner or a blocked vent in the breather box