Flat down low, flat mid, but Rocket at high revs?

[Ecarta]

Yes you heard that right. After a full engine rebuild on my 2004 KDX200 the power delivery is way off. Power Is very flat at low and mid rpms, even mid high rpms. But if you really let it scream, the power suddenly goes up 300%. Why do you think it's doing this? What are the most likely 5-10 issues to check first in your opinion?

Here is a list of things that changed since it last ran well:
All seals have been replaced
New crank and main bearings
New piston and rings
New Boysen Power Reeds
Stator plate moved about a millimeter CCW (an effort to gain top end power)
Clean air filter
Gas used was 4 month old premixed filled to top in plastic container...its all I had at the time!

Let me know thoughts, thanks!

[SS109]

Check that your powervalve is operating correctly.

[Ecarta]

SS109:
What is the best way to go about this?

[Molly's 70]

[SS109]

How I would start is to do like in the video above. The gear should move at a certain rpm consistently. If that checks out good. You can then pull your exhaust pipe and operate your powervalve by hand making sure the center and both subvalves fully close and open.

[Slick_Nick]

Well done on the video!

[Ecarta]

Check that your powervalve is operating correctly.

I know its been awhile.....but FYI....the power valve was barely working and not timed correctly...Once I got it timed up, it ran great!

As always thanks for your input!