RIght now I'm working on a C10 Chevy, but having a few problems.

Could anyone tell me if the valve timing was off, could that cause the truck to backfire and die? Or is there maybe another reason why the truck won't start?

Welcome aboard!

You don't give us a lot of information to go on.

It could be backfiring for a lot of reasons, burnt valve, fuel starvation, bad distributor, bad plug wires.

What is this motor, what's it in, and what have you done so far???

Larry

The timing being off could cause that kind of problem. Unfortunately, it could also caused by several other things as well,in addition to the things Larry already mentioned, such as vacuum leaks, firing order being off, carburetor problems, etc., etc. As Larry said, there isn't really enought informatin in your post to make a good guess about what's causing your problem.