[Hectic]

Lot of trial and error.
when you are testing are you putting some screws back into the gearbox (like 4 corners basically) then checking the spin and play? I did this before got em shimmed perfect then after screwing it down its too tight.
Also, what motor, battery and how heavy of a spring? Most stock motors won't pull a 350-400fps spring on 13:1 gears, even with a big ass 11.1 50c lipo.
depending where in Toronto you are located we could perhaps hook up and sort out the issue together.