This is a problem I have seen before. It is what I described earlier. The base problem is ussually the pickup rotor is not clocked properly to the spark rotor. Somehow messed up when distributors are made new (aftermarket) or rebuilt by A-1 Cardone. I think they make the shafts from a different distributor.
From my website.
http://www.12bolt.com/distributor_blueprintingI did look thru Georges Old distributor and found exactly what is described above.
Testimonial from George in Wisconsin,
I own a 1957 GMC 100, a ½ ton pickup truck. After buying it and driving it for five years, I removed the tired 270 inline six and 4-speed manual transmission. I then removed the truck’s front clip and welded in a Fatman Mustang II front end with rack and pinion steering and 13” front disc brakes. Next, I lowered a GM 292 inline six with lump port head connected to a TH 350 automatic transmission. I bought a distributor for the 292 from e-bay. When everything was ready, the engine started and ran well until I tried to hook up a vacuum line to the distributor.
The engine would often backfire when I let up on the gas, and it would bog when I took off from a standing start. I’ve had neither problem whatsoever since I installed Tom Lowe’s distributor.
The engine conked out immediately each and every time I tried to hook up the hose from a different vacuum source. I figured the e-bay item just wasn’t up to the task. So, I ordered a Summit distributor for $200, or very close to that price and installed its distributor. Guess what? The engine conked out each and every time I hooked up the distributor to vacuum. I thus drove the truck with a distributor. minus a vacuum line hookup for a year and one-half.
When Tom Lowe was told of the problem, he promised he could build a distributor that I’d be able to hook up to vacuum. Personally, I didn’t believe him, but I said if his distributor didn’t work as promised, he’d have to refund me my money plus shipping, no questions asked. He agreed.
After his distributor arrived, I installed it, hooked it up to a vacuum line at 18 inch Vacuum. Voila, the engine purred like a randy lion. Better yet, the truck has run a lot better at Interstate-plus speeds, it gets better gas mileage, and I’ve driven it every day since May and have had no problems whatsoever. Tom Lowe’s distributor has made a believer out of me.
George
