Oh yes, the ever so fun derailleur fix

I bought a older 10 speed and I'm trying to set the gearing but my rear derailleur is popping.

Here is the scenario:
On bike, going down road.
When i peddle hard, to push the bike to go faster, the shin pops and I get a small jolt
I change gears to second, nothing happens, no pop
I change back to first, pops when I push hard

I've tightened the mount, played with the limiter screws and adjustments, readjusted cable tension, set shift tension.

Problems: Older derailleur, suntour cyclone rear, higher rear gearing on stock derailleur, and a bad pin in chain that doesn't bend fully - this isn't that bad, just off by an angle after it goes around a crank, but could be the problem

Any ideas? thanks in advance.

This is probably your problem. It's called a "tight link". You need to clean and lube the chain and then loosen the link: https://bicycletutor.com/stiff-chain-link/ . It could be that your chain is worn to the point that it's skipping on the rear cogs. If this is the case, replacing the chain and the cogs is the only sure fix.

Exactly what I was thinking, but I'm kinda of a newbie with some of this stuff, thanks man.

I just had this same type of problem and found that my small gear was worn and that was causing the chain to jump. As soon as I changed my gear cluster all was good.

It's a new gear cluster, it's had probably 200 miles on it.