3600-4200 is a pretty big swing. It should be engaging within 50 RPM every time.
If its at 3600, you could get it down depending on current spring height. If its at 4200, it will require more changes.
https://horstmanclutches.3dcartstor...ClutchInstructions/GreasedLightningManual.pdf
It’s a old Horstman. We had several when I raced karts and this is one we never ran. I was just a kid then though so I know nothing lolCheck your disk clearance for sure, but if that's right, I would think you would only have to back the springs off a little. Turn the screws about 1/8 turn, counterclockwise, and tested it.
I'm not familiar with all the clutches, who makes that one?