My truck has recently developed a problem. It's a 77 with a 302 Holley 500 cfm 2 barrel and C4. It will fire up on the first turn of the key every time, but I have to let it sit and warm up some and while i let it sit and idle to warm up it will give me a little backfire pop every now and again. Then when I go to take off if sputters and sounds like its only running on about 5-6 cylinders. When I get to a stop sign if I give it too much (anything more than slowly pushing the pedal) it will sputter and sound like it dies completely then jump back to life. If i slowly push the pedal it just sputters cuts out a little and shudders some until it gets up to speed (I'm sure irritating anyone behind me at a red light or stop sign).

Once it's up to temp it does better and doesn't sputter really, but still doesn't have the throttle response it used to have. And sometimes while at a stop I can tell the engine is vibrating a lot and shaking the truck and the idle will drop down to about 450 rpms for a second and sound like the truck wants to die, but it doesn't and it comes right back up to about 550-600.

EDIT: I left out that now when slowing down it makes a gurgling sound in the exhaust, it's always done it some but the gurgling seems much louder and noticeable now.

I have a vacuum gauge hooked up and idling in gear at about the 550-600 range it's right at 16 inches of mercury, idling in park at 950-1000 it's steady 20-22 inches of mercury. So I think the engine is okay.

So far in trying to fix this I've replaced the fuel filter and the spark plugs with Autolite 25's (same as what I had in there). The old one didn't look too bad to me but since I had bought the new ones I figured I'd go ahead and replace them. Here's what the old ones look like.

1 thru 4


5 thru 8


What do you guys suggest I try next??? Sorry for the long story.

 

Update , (even though no responses) someone may be having some issues and this thread come up in a search.

I took the carb apart and sprayed it all out with carb cleaner and then followed up with the air compressor. Adjusted the choke cable and idle a bit, changed the fuel filter, fuel pump (because after replacing the fuel filter with a clear one I could see there wasn't hardly any gas being pumped) , accelerator pump diaphragm, PCV valve, and air filter. It ran great this morning, I had great throttle response with no hesitation, sputter, or miss. I hit the gas and it went! Hopefully it stays that way.