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NovaPwr
06-05-2008, 10:02 AM
I am asking this for a friend of mine who keeps his 78 Camaro with a pretty well built 502 in a storage building of mine. Over winter he pulled the front end sheetmetal off and then lifted the engine out and replaced a couple of gaskets and painted stuff up. He never disturbed the dist. Reinstalled the motor and has had nothing but trouble since. Motor seemed to be running well at first but now it pops and backfires when accelerating. He is using a GM HEI ignition and has replaced the module, rotor, wires, changed out the cap, drained the fuel out and replaced it along with the spin on filter. I checked his timing and it is spot on where we set it last summer while it was running good. He also had another friend run the valves and check for any broken springs. All seemed well there. The carb is I think an 1180 Holley. I looked to see if it had power valves but they are a solid plug in there. The spark plugs are a nice even tan color and look to be in fine condition. I am no pro, just a weekend mechanic that does his own work so I could sure use some help. What else should I check? I have to go to my grandsons ball game tonight and he asked me what else to do? Also, about the 3rd day he had it running I checked his firing order and he had the 3 and 6 plug wires swapped around. While that improved the problem, it did not solve it. Also, there have been a few times he says it will suddenly run like it should......maybe a short in the electrical supply to the coil? I was going to have him run a direct 12 volts to the dist. and see if that improved anything. And unplug the tach just in case it is shorting somehow....? Appreciate any help with this. I just don't know what else to do to help him and I know you guys know a LOT!
Thanks,
Dave

Vegas69
06-05-2008, 11:21 AM
First of all...I would check for loose connections in the ignition system. Secondly I would be looking for an arcing plug wire. Last would be looking for a gummed up carb from setting and not draining the bowls.

*hotrods*
06-11-2008, 05:55 AM
I had a buddy of mine that had the same problem and it turned out to be a ground. Also, when he replaced the wires were they pre-assembled? Check the ends of the wires and check to see if any of them may not be contacting.

camrat68
10-10-2008, 07:52 PM
I had a similar problem with my 502 due to a loose internal B+ starter connection. When I pulled the battery cable off of the starter, I must have rotated the post inside the solonoid which led to intermittant voltage to the choke and caused problems similar to what you've described. Once we found the problem and tightened the post, the problem has dissappeared completely. I have a gearVendor's overdrive and it was playing hell with the computer which was the dead giveaway that it was electrical in nature and not a timing issue. BTW- check all grounds if he repainted the car. That one got me too...