Well, had a moment to play with it. Backed out all the lifter preload, still can't get the intake valve to seal at the proper time.
I ended up hooking up the leak down tester and running only like 20 psi of air in to the cylinder. Enough to hear it but not enough to do the actual test. I then slowly spun the engine around by hand, several revolutions, both listening to the hissing and, since I don't have the intake manifold on, watching the lifters raise and fall. Also, I decided to try it on the the worst cylinder. The one that had the previous leak down test of 72psi being put in and only reading 20 psi staying in.
As I turned the crank, very slowly, there is one very small moment where the intake valve seals and no air comes out of the runner, but, instantly, the exhaust opens and the air starts coming out of exhaust. Even looking at the 4 stroke animations, it seems there should be a good amount of time that both intake and exhaust valves are sealed as the piston compresses the mixture. I don't have that.
Here are some things I'm thinking-- before I pull the head off.
1. The heads came from marketplace with the TFS stronger springs already installed. I took them off during cleaning, re-measured the height and re-shimmed as required. If I recall, most places required 1 more 0.015 shim then they previously had. Could I have messed something up here that would cause my issue?
2. In the TFS spring instructions, it said the keepers for the springs come in 2 bags-- 1 for exhaust, one for intake. The keepers were already on the valves when I got the heads. Could the previous owner have mixed them up? Would that cause my issue?
3. Can the cam be so much defective that it doesn't open/close the valves at the right time? Does that even happen?
Any other ideas? Thank you!