I have a 1978 z28 with a 350 in it, I recently replaced the distributer, plugs and wires. At first I tuned it by ear and with a vaccum gauge to highest vaccum as suggested by another forum as I was driving into town it developed a ticking noise at first I thought exaust leak I will deal with it when I have time, I was going about 65 to 70 when it started and slowed down to listen. When I put my foot in it to regain speed it started popping like a weird sounding backfire. It continued to click and everytime I gave it gas it wpyld backfire, itdid that for 5 mins then went away. When I got to town I thought well maybe timing was screwed up so I used a timing light and timed it to 10 degrees of center and drove home. Everything was fine until about 30 muns later it did it again. This time it would not go away so I pulled over to look if it was a loose plug wire or one arcing off the manifold but foynd nothing, still ticking. Started it a couole times still there. I decided to just limp it home. Got on the road and it slowly faded away to nothing. Any info as to what I should look at would be very appreciated.

 

It sure sounds like a plug wire shorting out,do you have headers on the car?
If you can maybe pull one plug wire at a time when it's doing this while it's running (best to have insulated plug wire pliers) until you find the one that's causing to problem.

 

no headers just stock manifold and was under there last night wiggling on plug wires no change, one was on the manifold and had a black spot but after moving it still no change. Should i replace that wire because of the black spot. In saying that i was think that the blackspot is just the rubber getting hot and discolored could be an arc mark though.

 

Was it ticking at the time? Your wires should be isolated for any contact and I would suspect that "black spot".
If it was ticking and or missing wiggling isn't enough,you need to fully disconnect each wire,those hitting as they should will make a noticable difference in how it runs ,any not firing will not and you'll know that wire or plug isn't firing.
Be careful though as you can get a nasty shock.

 

If you ground out the suspect wire the ticking should stop, You will have a dead miss but no ticking.

Black on anything electrical is a bad thing. Wire burn things will lean more towards brown and a melting looking. A black spot I would suspect of carbon tracking (from electrical discharge). If you are hearing a snapping at low RPMs / low loads then I would guess it should be a full miss under load. You could also wrap and bunch of rubber around the black spot and see if it changes. It is not in anyway a fix, just a test. Wires should be replaced 5/7 years on a daily driver and 10 years on a garage kept weekend warriors. Scope is the only real way to know if you wires are good and getting your car hooked to a scoop costs more then new wires.

Are you sure it is an electrical snap sound? 78 is in the middle of the Soft Cam issue GM had. This would only be a possible issue if the Cam is the original one. GM had to extended the warranty on the Cam to make people happy. It is a little before my time at the Dealer but the machinic that where there used to talk about doing 2 Cams per day. It basically effected all GM V8's 77-82. I believe GM tried a new case hardening process that worked most of the time. At lease enough to get through the original testing. If the harness fails 1 in a 100 that is a lot of cars especially over 6 years.