Replaced Q-Jet now missing on half of the cylenders

[Kritter]

I have a 73 w 350 that was running fine using a junk Q-Jet.

I replaced the junk Q-jet with a refurbished Q-Jet.

It was running fine with the old one other than a hesitation at low throttle, once I got the new one on it is missing on half of the cylinders. It was running fine with the old carb but now missing terribly.

I cleaned the distributor cap, and contacts in the cap, checked the plug wires but to no avail.

The choke is supposed to be manifold driven (little box on manifold) but my manifold doesn't have one. I've just been feathering the choke. Adjusted the cold idle so it would run when I started it, haven't even gotten to the warm idle.

Mixture screws are adjusted to 3 turns out, was 2 1/2 moved to 3 but no change.

Strange though, it would run before with the timing set in various settings. Now it won't fire on all cylinders no matter where the timing is set. When I let it run (missing and all) about half of the exhaust headers are cold, and the other half are hotter than heck. Hotter than when it was running on the street before.

Help

 

[Kritter]

I picked up a new Distr Cap and will try and rule that out, new plug wires, and plugs so not worried there.

If the new cap doesn't fix it, I'll be Pi$$ed.

 

[WETVET]

I think you have a vacuum leak at the base of the new carb. Try exchangib=ng the new for the old again and see what happens.
The gasket at the base may be damaged.

Good Luck.

Steve

 

[BeaterShark]

Initially, was the carb the ONLY change made from when it was running OK to horrible? If so, I'd leave the timing and everything else the same and work on the carb.

At this point, I'd put the old carb back on and get it running good again. Then, swap the carb and begin troubleshooting the carb.

I'd start by checking the following:
Check for vacuum leaks (will the engine run with hand sealing air from entering carb? Do you hear loud hissing noises?)
Make sure all unused vacuum ports are plugged.
Are the rods/jets the same between the two carbs?

 

[Kritter]

For those interested I found the problem. When I replace the old quadrajet with a remanufactured one from Advanced the float bowl was stuck. It dumped massive amounts of fuel down the manifold and fouled the plugs. Similar to what happens on a 2 cycle dirtbike.

After four carbs, exactly the same from Advanced finally got one that wasn't messed up. Runs great, no flat-spot on acceleration it's a beautiful thing.

Now just need to get the HEI distributor modified so I can achieve full 35-36 degrees of timing.

Kritter