Kawasaki 650, no top end

OK it's a 1990 Kawasaki TS, stop laughing, I have a few questions.

First off I'll say that it ran this last 2 summers, but not very
great. It's missing its top end. With it out of the water it will start to
miss before it over revs.

When riding it I used to let off the throttle when getting some air so it
wouldn't rev too high, but now that isn't a problem, it doesn't over rev. It seems to be at top speed at around 3/4 throttle, giving it more throttle just changes the tone of the exhaust but not the RPM's.

Also ever since I owned it (around 1992?) it took a little warm up period (30 seconds?) at half to full throttle until it would stop missing and be able to get up and plane easily. Then the low end is fine until it gets cold again.

The carb has been rebuilt and adjusted per factory specs then
attempted to fine tune it, no help.

The compression is 160 psi cold and 140 psi warm, even across both
cylinders. Everyone keeps telling me this is fine, but the specs list
178 psi. That's a long way off! I even see supposed rebuilt engines
that said the compression was only 150. Maybe they aren't broken in yet???? I don't know, I'm lost. If the manual says 178 psi, how is 140 or 150 good?

I bought 2 "good" used reed valves. Well they were supposed to be
good. I don't know 2 cycles so this is new to me. The supposed good used valves are slightly open all the time. It's easy to see just looking at it. Both the smaller valves and the larger valves aren't sealed unless I apply light pressure, then they seem to
close fine. Flipping them over doesn't seem to help much. These
aren't metal, they look like thin fiberglass.

The spark seems to be the same for both cylinders and it doesn't vary when hot or cold.

Would good reed valves make a noticeable difference in compression?

This also sat 2 years outside without being fogged so I'm guessing
honing and new rings may help a lot? Can I just hone and install new
rings with the old pistons? (I guess I have to open it up first but
what do I look for?) Where do I get new rings?

Appreciate any help,

Tony