UPDATE: my challenger feels like its out of gas when i drive it hard

[505challenger]

i have a 73 challenger 340 4-speed.  the car runs fine until i open it up, it will pull just fine for a few seconds then it feels like its runnig out of gas.  the motor has a lunati cam, 10-1 comp, x heads, headers, performer rpm intake and holley 750 carb.  at first i thought maybe it IS running out of gas and the stock fuel pump just cant keep up and its sucking the fuel bowls dry,  but it doesnt just run like that for a second or 2, but runs like that for usually around 5-10 minutes (usually i limp it home and shut it off).  after it sits for a while it will be fine, until i open it up again.  i think it has to be electrical since it isnt really out if gas.  when it starts running like crap see that the carb is spraying fuel, and the engine is sucking it in when i crack the throttle.  i have changed the ignition module and coil and neither helped. oh and the reason i suspect that its electrical is sometimes when it does this the tack needle sort of jumps around.  i REALLY need to figure this out because im selling the car!!  http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=130432205793&viewitem=&sspagename=STRK%3AMESELX%3AIT

[72cudamaan]

My guess is a pickup coil going bad.

[505challenger]

whats a pickup coil?  is it in the distributor?

[mopar12372]

check fuel pressure / imop the fuel pump is toast(look to see if theres fuel in the bowls when it starts acting up). if you have an engine that is NOT stock you need to install a higher volume fuel pump, i would go with a mallory 140 with return style regulater. if the fuel system is ok how long has it been since you replaced the ballist resister (if you have one )its part of a tune up , they can test good and be bad .next i would ohm out the coil when its hot after it starts acting up (not cold). check all ignition wireing conections ect . test one area at a time and make 1 change at a time so you can single out the problem.

test the simple things first , there is more to what i said just keep it simple!

[mopar12372]

check fuel pressure / imop the fuel pump is toast(look to see if theres fuel in the bowls when it starts acting up). if you have an engine that is NOT stock you need to install a higher volume fuel pump, i would go with a mallory 140 with return style regulater( simular type fuel pump and regulater or what ever your pocket book allows). if the fuel system is ok how long has it been since you replaced the ballist resister (if you have one )its part of a tune up , they can test good and be bad (create headaches like this).next i would ohm out the coil when its hot after it starts acting up (not cold). check all ignition wireing conections ect . test one area at a time and make 1 change at a time so you can single out the problem.

test the simple things first .

[505challenger]

UPDATE , ok so its obviously not ignition related, ive tried a new coil, pickup coil, ballast resistor, ignition module.. heres a new clue, while i was screwing around with it i knocked the BIG vaccum line off of the brake booster and nothing happend, it was sucking air like crazy, but didnt die, or even affect the idle??  how is that even possible, i can put my finger over the line and it IS sucking.

[Bullitt-]

I would guess that you have a bad enough vacuum leak that the hose coming off did not add enough air to change anything, one other possibility is the throttle is open & your not on the idle circuit but that would not explain the loss of power. 

[wiging19]

This probably doesn't apply but if you replaced the sending unit or added a new sock on the end of the sending unit that could cause a problem.   I had the same problem when I put a new filter sock on the unit.   My car would drive great then die from fuel starvation because it takes a while for the filter to fully open up.  At least that was my problem.  In time it went away but had me going for a while till I figured it out.

[Bullitt-]

i knocked the BIG vaccum line off of the brake booster and nothing happend, it was sucking air like crazy, but didnt die, or even affect the idle??  how is that even possible, i can put my finger over the line and it IS sucking.

  You should also know that the leak from the brake hose should have Increased the idle speed.... To confirm the vacuum leak cover the carburetor throat & the motor should die, if it does not you know you have a pretty serious vacuum leak, if it just slows down a small leak.

[Chryco Psycho]

you can have a leak inside the booster , so your engine may be adjusted to compensate for the leak in the booster ,get the booster repaired , it should hold vacuum