I recently picked up a 1981 Conquista (305 V8) in Seattle. A previous owner pulled almost all the emission system out (Air pump, AIR injection tubes, EFE actuator, EGR valve, air cleaner) and replaced the original Rochester with a Holley. In order to get a smog certificate (required before it can be registered in CA) where I live, I needed to replace the emission system (many long, hot hours scouring junkyards took care of that) as well as the Holley that was on the car when I bought it with a Rochester 4MV. I bought a new/rebuilt Rochester but notice that once the engine warms up, when I hit the gas the carb bogs/hesitates. This is especially noticeable from a dead stop. Before I start tinkering with the carb, I would appreciate any suggestions on what the cause might be, as well as how to fix it.

There's a good chance it's secondary bog (untuned Q-jets are good at that). Since it's a new carb, some causes (like a failed secondary choke pulloff) are probably not candidates (though you should check), but there are a variety of things to play with.

I don't know about other threads, but this one:

http://www.necoa.org/postp6827.html&highlight=&sid=900b49f7bdfdfaa691fec3a07cb6d093#6827

has some Q-jet discussion and at the bottom some links to websites that discuss tuning the Q-jet. Once you get it dialed in, the Q-jet is a pretty solid carb, but out of the box they usually need some tweaking to really run tight.

Be sure to check that fuel pump pressure before giving up. Those things can be fickle and are a real pain when stomping the floor doesn't work. :-)

The web sites reccomended are an excellent start to understanding the Rochester. Thanks, I'll let you know how it works after I read and digest them...

I don't know if you figured your problem out yet or not, but here is the situation I ran into...This isn't going to be a very good description because I dont remember the exact details of what caused my problem and dont have the car here to check it out again. I had a similiar problem where my car would act like it almost wasn't getting gas when I first hit the gas, then it would run fine once I was in the throttle. It turned out it was because the bottom part of the chrome air filter cover on it was hitting (this is where it gets vague) something on the top of the carb. If I loosened the wing nut on the top it worked fine. I ended up denting in the bottom of the air cleaner cover so it cleared and as long as its in the right spot it runs like a champ.
Hope I was of some help...if not atleast I entertained myself for a few minutes :)

After reading your post, I checked the air filter and with a little looking around found that the vacuum line from the charcoal cannister to the carb had wound up sitting on the exhaust manifold! Needless to say, the line had melted and fused shut so I had inadvertatly created a vauum leak which apparently caused the problem. I cut and spliced the vac. line back to the carb and the engine has been running fine ever since. Hard to believe that a vacuum leak could cause such a dramatic difference in performance - I would have bet my next paycheck on it being a carb or ignition problem. Thanks for the advice.