Try the gauge in another cylinder to rule out the gauge. That bouncing sounds like a gauge issue. Going from 80-200 psi sounds like a ring/piston problem..two different problems occurring at the same time?

If you are going to put pistons in, don't let them bore it until the pistons are numbered and in the machinists hands. The bore sizes are slightly different, IIRC number one has a different clearance than 2-4.

X2 on putting air in the cylinder to see where the leak is at.

Good luck and keep us posted!!!

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