Ignition problem (I think)

[Wayne Maybury]

OK, here we go. I will try to explain the problem to see if anyone has any ideas that may help. This car has been on the road for 5 years and never given me any problems at all.

I have a 351W with a 750 dp Holley, mechanical fuel pump, solid lifter Comp cam and all the other regular goodies. Ignition is via an MSD distributor, MSD Blaster 2 coil, and an MSD 6AL box.

Here is the problem and what I have tried so far. Once the engine has been running for about 5 to 10 minutes from a cold start and has just heated up to the normal operating temp, it begins to mis-fire, buck, back fire, you name it. I can just barely keep it running. The car will move in first gear if I don't press too hard on the gas. Going up a gear or pressing too much on the gas results in worse operation. When it did this the first time, a friend thought that a float needle maybe sticking. I took the Holley off, pulled the bowls, pulled the float needles, everything was clean. The power valve was also checked and was fine. The fuel filter had a couple of little specks in it but no big deal. Fuel levels were checked. Put the carb back on, same problem. Fuel pressure is 5 to 7 lbs so the fuel pump is not the problem.

Now for the really strange part, if I shut it off for just a couple of minutes, it will start right up and run normally but in a minute or two it will begin to miss, buck, etc all over again. It really appears that this problem is heat related. If I shut it off for an hour, it will run normally for 5 minutes then start to act up.

I thought that maybe it was the coil. Changed the coil, same problem. Checked all wire connections, grounds, etc. Everything appears to be normal. Called MSD, they suggested a couple of tests including removing the wire from the center of the distributor, tunring on the key, jumping the 2 wires that feed to the box from the distributor to see if the coil will arc from the wire which is placed a 1/2" from a ground. Lots of spark. MSD tech says that this test proves that both the coil and the 6AL box are working normally.

With virtually no where else to turn, I ordered a new pickup coil which I should get in 2 or 3 days. The parts supplier said that he has not sold an MSD pickup coil in years but I was the fourth person to order one in the past 2 weeks. Strange coincidence but no help to me.

Anyone have any ideas? Don't tell me to check the gear on the distributor or the timing as the engine will run normally if it is allowed to cool down, even for just a few minutes. I cannot go far from home to test it as I am now affraid that it may crap out completely. Each time it acts up seems to be worse than the time before.

Regards,
Wayne