Hey guys I need some help so I have been slowly restoring my 84f-150 4x4 it has a 302 with eddlebrock intake and Holley 4160 600cfs carb. So all of a sudden it has started backfiring when it gets ready to shift. Any ideas? Also sometimes it runs like a top then gets up to highway speeds like 70mph then slowly starts to sputter then backfire.
Could this be my timing?

 

Usually due to water in your fuel. Replace the filter definitely first. Add a water remover additive to your fuel (must drive it often enough to have this help). If the truck will be sitting for a long period of time, drain and clean the tank. It probably could use a good cleaning too if you're working on a resto.

 

I had an older truck that did that, so I disconnected the smog pump and it stopped.

 

Well guys it's a daily driver so it goes through gas and I already have done away with smog pump so I'm stumped now

 

1. Timing
2. Plugs and plug wires
3. Distributor cap / rotor button
4. intake/exhaust manifold gaskets
5. Stuck exhaust valve

That's what else I can think of off the top of my head.

 

"Going through gas" doesn't mean you don't have water. At a minimum change the filter.