Responding in order...
I removed the reed valve and it looks fine. I'm going to replace it but am waiting on a part quote.
The prop is a ParaJet 3 blade. My motor is a ParaJet Volution 2 with an XT172 motor.
No, I haven't checked the plug on each flight. It's been six months since I was able to fly and it didn't perform well on the first flight, so it's been grounded since then while I try to troubleshoot this. During the flight, it maxxed out at 6500 RPMs. I let off on the throttle to loase some altitude, then when I maxxed the throttle again, I only got 5500 RPMs. The top end RPMs have been very inconsistent.
I have changed the spark plug three times now to be sure that wasn't the problem.
In addition to the reed valve, I'm also going to replace the carb. I rebuilt the one I have but I'm running out of ideas.