Well... I got a poorly running slant that I'm at wits end with and ready to replace, but I'm still willing to give it a second chance. Maybe one of you fellas can help me. Please. No one else has been able to help or even try to explain it.
My '74 Duster has never ran right since I bought it. The engine isn't original and had been swapped in prior to my purchasing of the car. It is a 1977 Super Six out of I presume a Volare. It had a bad off idle hesitation that would kill the engine. I chalked it up as a carb issue and figured a carb rebuild would set it straight, it didn't. I've managed to decrease the size and position of the dead spot, but I can't get rid of it no matter what I do.
The back story:
The engine has had a complete rebuild. The rebuild wasn't initially intended but when I pulled the engine out to fix a bad rear main seal shortly after buying it I found cam bearing material all over the inside of oil pan. I installed federal mogul main, rod, and cam bearings. Cleaned up the cam, rebuilt the oil pump, polished up the cylinder walls, new gaskets, rings, timing chain, adjusted the valves, your basic rebuild. Everything was federal mogul or fel-pro, timing chain was a cloyes. Brand new ignition, plugs wires, cap, rotor, and vacuum advance. All Borg-Warner, and Autolite parts. The factory exhaust was replaced with 2 1/2 od pipe.
For the intake the studs are original, the intake hasn't been surfaced, but I pulled it out last week and inspected it. The gasket showed no signs of leaking. The egr had been wiped out prior to my purchasing the car. Someone had cut and beat out the wheel and flap inside the exhaust manifold and replaced it with a bolt and made a block off plate for the intake. For the intake stack everything was installed and torqued to Chilton's standards during my rebuild and the recent reinstallation of the intake.
The engine doesn't have a vacuum leak, it isn't sucking exhaust, the compression test was perfect, and the vacuum and mechanical advance are operating correctly. Mechanical this engine has nothing wrong! It just doesn't run right.
The engine has had six different carburetors on it now, ranging from new out of the box to rebuilt from the local scrapyard. The issue has remained constant through each carb swap showing it isn't the carb. It prefers a Motorcraft 2100 1.21 venturi (way too big, I know) with the timing advanced to 22 degrees.
To help the timing issue I hooked up an OSAC valve backwards, I was able then to bump the timing back down to 12 degress. This has helped more than anything. The dead spot is now around 30 mph or about 1/3 throttle, no longer off idle. It stumbles, coughs, sputters, and surges all over the place if you hold the throttle constant, but refuses to die. Simply letting up, or pushing the pedal down just a hair instantly overcomes this dead spot. It is the oddest thing I have ever seen.
The dead spot is noticable upon acceleration both from a stop and cruising down the highway, but the engine shrugs it off unless you hold the throttle constant in the "dead zone."
It seems like the engine is missing something, but I don't know what. I'd hate to get rid of it, but unless it gets its problem sorted out, I see no other option.
