Well, it's my turn to ask for suggestions..

318willrun said
170 psi says it has plenty of compression to run. For instance, 3 cylinders showing 50 psi would indicate a problem. The engine came with remanufactured heads, I'm sure, which included new valve springs. Not high performance valve springs, just new replacement springs is how parts store motors would most likely build it. I'm really doubtful valve springs are the issue here. Again, I've shared about all the info I have on the motor. I did not buy it new, it was from craigslist. I just took enough of it apart to verify it was new.

It has plenty of compression, yes. But what's in the cylinder? You need compression, spark, and fuel (air fuel mix). If the cylinder is partially still full of exhaust, or the incoming air is facing hardships just to enter the cylinder, you can have all the pressure you want and it will still run like ****. I've taken several of these engines apart. Mass rebuilder stuff is out and out the worst. They do not remanufacture. They repair used parts, and modify the worn crap to work with it. Like using guide liners that are thicker, and turning the valve stems smaller because replacing guides and valves ads to the rebuilding cost. I've also seen valves that were turned down until they were .100" smaller in head diameter because that's what it needed to get a seat angle cut on it. It's not a big deal if the valves are sunk - it will still run and have good cylinder pressure and you can whack off the ends of the stems to keep them sort of even. Of course you ground through the surface hardening of the stem but it only has to go through the 12 month warranty. The springs are not normally replaced. Instead they have thick shims under them to bring them back into tolerance even though they are whipped. Those you can see with the valve cover off. It's my opinion that you did not take it apart far enough, or you missed some things. It's running - which means it's passed the quality control of the rebuilder who only cares that it runs for the least a mount of investment on his part. The peformance is telling you there is a problem or a series of them. I hope it's something stupid like a rats nest or whatever. It's not the cam although that cam on factory springs won't work well either.