Ok, so i know this isn't really a HAMB worthy ride, but yesterday I picked up a 67 c-10 it has a 327 with headers, 650 holley double pump, edelbrock torker intake, MSD electronic distributor, newer plugs and wires, probably a few other things in there too. on the way home yesterday, it has a rough idle, and when accelerated, it stumbles and wants to go but misfires. I'm thinking its just the plug gap or the ignition timing? the guy seemed like he knew what he was talking about but couldn't tell me why it was misfiring.
The possibilities are endless, but rule out old/bad fuel first. If it's been sitting, he may have poured some gas from a can and inadvertantly introduced moisture into the system. Get a catch can of some sort and pull one of the lower front float bowl screws out to drain the front float bowl, this will be a good sample. Smell it, this will tell if it is fresh. Let it settle and look for water, it is heavier than gasoline so will be at the bottom and be obvious.
One of the most ignored part on these kinds of things is the ignition wires, because a new set costs more than a new set of spark plugs, so guys kind of ignore the possibility. You can't look at a set of wires and tell, they might look like new when they're 5 years old. It's hard to test them. Even with a plug wire disconnected and held a half inch from the motor it might be bright/hot and blue, but when connected it might be breaking down and not delivering a hot spark to the plug.
Bus, I'd look at the plug wires. You say it has headers, so its easy to get the plug wires near the headers and burn them. Alot of back firing thru the carb tells me the plugs arn't working right. So if you find a bad wire, the plug from that hole is probably full of gas and not firing. N.N.
Try and check the distributor vacume advance. Probably you'll find it's set up to backwards of what it's supposed to, then recalibrated around that to make it not seem so bad. Just walking up to it I'd set TDC and prove it with light, then proving advance control function mechanical, then I don't know the rest of your set up. Standard is to get advance with vacume applied, standard goof is to hook up to manifold so you loose vacume when you should have most.
How long did it sit before you bought it? Better do an intro, some don't like the first post to be OT.
All of the above and check to see if there is alot of black carbon on the plugs. Fuel that has been sitting for a while will leave heavy deposits on the plugs.
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