May or may not be THE Pontiac Guru of thegroup, but do hasve a lot of experience with them. (Might want to bounce this one off Mr. Fixit also)
Somehow, I don't think it's the carb either, but need more details. Plugs fouled, with fuel or
oil? Black liquid out the exhaust, fuel or
oil?
If fuel, if it were running that rich (like no jets at all in the primary metering block), if the motor would even start, I doubt you could get the car out of the driveway before you started having problems with it. A closed choke might give you similar symptoms, but a lot sooner than 50 - 75 miles. And the motor would run like crap.
Is the cam dialed in correctly? Is the ignition dialed in correctly?
I'm thinking
oil, rather than fuel. And oil can only get into the combustion chamber in a few ways. Past the rings, past the valve stems. (Pontiacs are notorious for drinking oil down the valve stems when the seals let go) That's the obvious ones. Oil getting into the intake by some other means are less obvious.
I would put Pontiac engines in the same class as Ford FE's in that it's been 20 - 30 years since most machine shops have seen one, and they do have their quirks. (I could still build a Pontiac engine in my sleep, but would ask for a lot of advice with an FE)
H-O Racing Specialties in Hawthorne CA was where the real Pontiac Guru's resided, and they may still be around. Check for postage stamp size ads in Hot Rod, PHR, etc.
Why did you use a 400 instead of a 455? The blocks are identicalfrom the outside and you can't tell the difference unless you know Pontiac casting numbers. The Edelbrock P4B or Performer RPM will give you better street performance than the Torker.
This is a little off-topic for a Cobra site, although most of us came up through the Musclecar ranks. If you want to go off-line with this, I'm at
jwalsh21@ix.netcom.com.