So I just finished installing the Edelbrock 2027 Power Package with aluminum E-Street heads, a mild cam, lifters, pushtubes, roller-rockers, intake, and a 500 cfm carb on my 1978 Ford F-100 with a 302. The truck ran great for 500 miles. The only issue was that there's an exhaust leak on the passenger side manifold and so on deceleration it'd backfire. All of a sudden last week the backfire disappeared and when I'd accelerate there'd be a rapid irregular popping (can't tell if its exhaust or the carb - doesn't show up when its revved unloaded). The truck hesitates and stalls with the popping and if you really get on it, you can kind of fight through the popping. The popping/stumbling is getting progressively worse. It mostly happens under load at higher rpms. The cam was broken in properly, overhead has been run and double checked and fine-tuned twice. Timing has been set and checked; there's a new chain and sprocket on it. The fuel filter was pretty dirty, so it got replaced last weekend. I was thinking of pulling the carb and giving it a thorough cleaning in case it got clogged if junk got through the filter. I don't know if that could be a cause of this problem or not. The stumbling leads me to believe that I'm not getting fuel, so I'm thinking the carb is dirty (I pulled apart the filter and it was BLACK after just 500 miles). I'm just learning carburetors so I'm not terribly familiar with troubleshooting them. The thing that really puzzles me is that it didn't show up for so long which is why I was leaning towards the dirty carb. Any thoughts, ideas, suggestions? I know the valvetrain could be suspect with these symptoms, I just want some input before I go back and tear everything apart again. Thanks.

 

It could very well be dirt in the carb. If the filter was filled with black gunk, probably a lot of really fine dirt got through it and into the carb. That happened to one of my cars that sat around for really long. It turned out that the gas tank got really rusty, and the filter would clog up very quickly. But the stuff that got past it built up a layer of mud in the fuel bowls in the carb. I had to get a new tank, and flush out the fuel lines.

 

Thanks for the recommendation. I'll start at the carb and look at the fuel system.