Classic/Antique Car Repair: 68 buick skylark custom - sluggish, buick skylark, fuel starvation

Question
i just had a freshly built motor put in this car.  the old motor was a engine built for speed (bored over / big cam)

i kept the carb (holley 650) that was on the old engine when we put the new motor in.

when the car is warm and has been running i get smooth acceleration if i don't hammer on the gas.

if i hammer on it.. either from a start or while i'm driving the car will accelerate but then start to bog and 'chug chug' slowly accelerate.  it's very poor performance.

the new motor is slightly bored over and has a cam one step up from stock.  nothing radical.. definitely something that could be a daily driver.

the car sat during my divorce and at least 2 times it went a while without being started.

the carb hasn't been cleaned - the jets are the same as they where with the old motor.

the car has new points/plugs - i haven't pulled them yet to see what color/condition they're in.

does this sound like a rich/lean problem?  which do you think?  timing?

where would you start to fix this problem?  should i rejet?  the car has headers/dual exh. and a standard open air filter/lid. (no scoop)  

Answer
Well, with all the non standard stuff on the car it is hard to guess, but from the symptom you describe, it could be fuel starvation.  I'd start by changing the fuel filter and testing the fuel pump to see if it is putting out the right pressure (3 to 5 1/2 PSI) and volume (fills a coffee can in around a minute at idle).

Then, the next step, if the problem isn't gone, is to find someone with an engine analyzer and have it tested to see where everything is set, and to check your vacuum advance unit to make sure everything is hooked up right and working.  It's very common to hook up the vacuum advance to the wrong port on the carburetor and cause all sorts of driveability problems, and since you have non - stock stuff on the engine, I can see that happening easily.

If the mixtures are way too rich, you'll feel some loss in acceleration, but you describe a much more serious loss of power, so I don't think it's the mixture totally, there's something else not right.  It's time to get some professional help, I think.

Probably, to get decent performance, you are going to have to replace the carburetor with the right one, but I think you have other troubles to fix first.

Dick