Let me set the stage:
I have a holley 4150 series double pumper on my recent 454 rebuild. The motor was dynoed at the machine shop that rebuilt it and the timing and carb were all set. I put the motor in the car and it seemed to run great for a short period of time. (30-45 min) Then, suddenly, it acted like it was running out of gas. (but guage said there was some in it, even though low) It would almost stall at slight throttle but if you stuck you foot in in away it ran. I did this all the way to the gas station. After fill up it ran better but not perfect like it was. At highway crusie at part throttle it seems to have a slight "surge" to it now. You can gently feel the car surginging.

Question: Is this carburation? Is it possible I have some debris in the carb. The reason I say that is we dropped the gas tank to put in new line and we could have dislodged something. Maybe just further adjustment?

Last note, the thing is a pig to start cold know. This carb on the old 454 started like a dream cold. Pull the manual choke out all the way, fire her up and immediatley go part choke and it would hold a fast idle. Now, the thing smokes and miss fires and won't idle until warm. It still doesn't idle well even when warm.

Where should I start here?

I may be wrong on this but it sounds like me the timing is to advanced. On my dads 78 Corvette with a 350, it would surge and backfire out of the carb but most of the time out of the exhaust. I dont know if this is really your problem. Hope i helped out.

Sean

check the float levels, and for a vacuum line that came off.

the first place i think i would start would be to dismantel the fuel bowls and clean them and take a look at the needle and seats to make sure there is no trash on them......after all looks good then replace the fuel filter. before you hook the fuel line back up shove it in a pop bottle or something and crank the motor and flow some fuel into the bottle......just incase there was any trash in the fuel line.....this would allow you to pump it out before it goes into the carb..........after a few shots of fuel into the pop bottle then hook the carbs fuel line back up........

then recheck the floats.......adjust if needed to be......fuel should just trickle out with a slight bump of the fender while the car is running.......

look down the carb while its running with a flash light and look to see if you see any fuel dripping from anywhere...there shouldnt be.....

reset you idle mixture screws to the highest vacuum reading.....

i think maybe you got some trash in the carb....

Yup, sounds like trash in the carb causing a lean condition at part throttle before the enrichment circuit opens.

i pulled the primary side bowl and metering block. (parts store only had one gasket set ) The was dirt in it. one of the jets was about half plugged. It ran 90% better.Still not perfect. Should I do the secondary side or is there no fuel going through the secondaries at idle??
I am also going to try re-adjusting the idle screws...I did a search here and found out how to do it.
Last question- my jet have #71 on them. what are doing if you go up or down in numbers on the jets?