Let me see if I undestand this time. Two clockwise clicks of the high-speed needle valve adjustment screw increases RPM by 1,000 and two turns counter-clockwise from that reduces RPM by 1,000? And one counter-clockwise click from 8,800 leans it out too much?

How many turns open is the needle valve?

That sort of sounds like the needle valve is fouled. This happened to my Magnum 80. Here's how I cleared it:

1. Remove the needle valve, and clean it off. Check that the O-ring is okay while you're at it.
2. Reinstall the needle valve.
3. Disconnect the fuel tank to carb fuel tube at the needle valve. With a spare section of fuel tubing attached to the carb blow low pressure air through the needle valve and the carb. Low pressure is something less than an air compressor would deliver, maybe 40 - 50 psi.

If you have a small obstruction in the fuel system the low pressure air should blow it out.

Hope that works for you.

Mike