Ok, I've read a lot of posts about engine noise due to clogged injectors, timing, etc.

My engine has about 3-4 degrees of timing chain stretch.

This noise I have sounds like a gas engine pinging on acceleration, like a spark knock sound. This engine is a replacement used engine for my original one. My first engine (the original) had this very same sound, I tried on the original engine adjusting the fuel timing and that had some change but never eliminated it. This engine (the replacement) has the same sound, no smoke that I can see in the rear view mirror, when backing up I can see a whiteish colored smoke, but that is it. No black smoke on acceleration.

I tried checking the IP timing when I adjusted the valves, but when you remove the check valve all the fuel runs down into the injection pump when it is at 24 degrees BTC. I use the hand pump to pump it up only for it to run back down into the pump.

This is what I want to know:
Does there have to be a certain amount of fuel in the tank in order fuel to stay in the pump??

3-4 Degrees of t-chain stretch, is that normal?? What is the MB spec on that???

If you take the injectors apart, can they be reassembled without affecting the opening pressure???

And, does the 3-4 degrees of stretch affect the cam timing enough to cause that noise??

Thanks in advance!