Ignition/Fuel Problems??? - I'm Stumped!

[Silk]

I’ve got an ignition issue – or possibly a fuel issue- that I can’t figure out. It’s gotten progressively worse over a period of almost two years, and now it’s approaching fatal. I’m hoping that better diagnostic minds than mine can help pinpoint the problem.

About two years ago, I noticed that the car would start up just fine, but after I’d been on the road for 4 or 5 minutes, it would stumble badly. Occasionally it would simply lose fire completely and stop. It would crank, but wouldn’t catch at all. After waiting a couple of minutes, it would start up and run fine. The problem didn’t occur every time I drove the car, but was more likely when the car sat for a week..

Over time, it’s gotten progressive worse. Now, every time I use the car, it will stumble and then die – no fire at all. I have to wait 3 or 4 minutes, then it will start, run rough for a few moments, then clear and run fine, but only for a couple of minutes. Then it’ll die again. After about three of these start and stop episodes, it’ll start and run rough for a while, then clear and run perfectly. Start it up the next day, and it’ll run fine. Let is sit for a week, and all the problems reoccur.

I was fairly certain it was a fuel issue, until I recently noticed that the tach (electric) would bounce all over whenever the stumble occurred – leading me to believe the issue is electrical, not fuel-related.

I’ve got an MSD Pro Billet distributor, no ignition box and no ballast resistor. I’ve replaced the coil and tightened all connections in the ignition circuit, but that hasn’t remedied the situation.

Could this be the distributor pickup gone bad? If it weren’t for the tach going crazy when the engine stumbles, I’d think this was a fuel issue (I have checked the fuel filter, and it’s clean) – but is there any way a bad fuel pump or debris in the carb jets could cause this? Other than that, I’m stumped – and would really appreciate any ideas you might have.

Thanks.