Home Forums Gear Hunting Trucks and Four-Wheel Drives Chevy 350 engine noise

My 77 K10 pickup has started to make a nasty noise and has lost a lot of power. The noise is "like" a knock but seems to be ignition/timing related rather than a rod or valve gear. It is not as regular as knock usually is (not in sync to RPM) and sounds like it comes from under the intake manifold. The noise stops at certain RPM ranges. The truck has also started to backfire up through the carburetor when it the engine first starts. This is not the original motor it is a replacement(of unknown origin)with electronic ignition.

I thought about pulling the timing chain cover but A) that is a lot of work for a troubleshooting exercise and B) I read on the internet (so it must be true) that it is virtually impossible for the Chevy small block to "jump" the timing chain. It seems equally unlikely that the distributor somehow "jumped" a tooth but something happened.

Any ideas? Tricks for isolating the issue?

Its only at $1500 beater but my only transportation at the moment. So I want to get it fixed but I an not anxious to drop a new motor in it. I'd more likely start looking for another beater truck if it can't be fixed pretty cheaply.

Thanks