'79 KZ650SR Power Problem

Hi guys!

So this is my first post on the site so sorry if this isn't the right spot or whatnot.

I am having some problems with my KZ650SR. It runs okay and everything seems to be in working order. Mostly. But, when I'm riding, I can only get up to about 65 mph in 5th gear, which isn't quite as fast as it should be able to go. The RPM's will only up to about 6000 in 5th gear and it feels like it starts to kind of sputter (any other gear, I have no problems with the RPM climbing towards the red). I have some friends that have helped me try to diagnose it. I checked the compression of all cylinders. They were about 65-70 psi. Which is low across the board, but I'm thinking it may have been the kit I was using (but I have no clue). Regardless, they were within 10% of each other. My buddy said I should check the cam chain. Checked it, and it hasn't skipped a link or anything. Everything looked A-okay according to the manual (Clymer). The ignition coils seem to be fine; all cylinders are getting spark. I have checked the carbs and the jets and everything seems to be clean and working fine. Next would be to check and adjust the ignition timing, but I don't have the tools for that quite yet. And then another buddy just suggested that my regulator could be bad or going. I'm at a loss and could use some help.

Has anyone had similar problems and fixed them? Or maybe does anyone have any advice on what to do next?
Thanks!

Have you checked the valve clearances? 65 psi is pretty terrible

Maintenance (like valve adjustment) is always a good place to start. Also, is the bike stock or modified. If it's running pods for example with the stock jetting that's a no go.