Misfire under load at low rpm

[martin owen]

440. Once motor is warmed up has mis under load. when i take off it hesitates have to give it alot of gas when i put car in park it goes away. Has new plugs and wires new coil and new edlebrock 750 carb. any advise would be much appreciated

 

[Lionized]

Fuel pump or fuel pump push rod?

 

[martin owen]

Has electric fuel pump

 

[tak419]

So when in park its running smooth ? Do you have a fuel filter that could be plugged, a kinked fuel line. It kinda sounds like it's starving for fuel under acceleration. That could also be a dirty carb. Any back firing or slight popping as you accelerate ? These are hard to pinpoint without being there. Plugs wires arcing anywhere or rubbed up against anything ? This could also be a vacuum leak. I chased the exact simple on my ZX10 motorcycle, checked stick coils, injector, electrical connections, everything. It was a slightly loose, I mean slightly loose rubber boot where the throttle body bolts to the head. Had a slight miss and no acceleration.

 

[Kern Dog]

My advice is to consider that it may be running lean once the choke opens. Have you considered using a ThermoQuad or a Holley 750?
Edelbrock carburetors larger than the 600 cfm seem to be hit or miss.

 

[CoronetDarter]

I have the 750 Eddy on my Dart (1407). Was having the same issue. Make sure the accelerator pump linkage is in the hole closest to the throttle body on the pump arm. When I bought the Dart the linkage was engaged in the bottom hole and was having severe hesitation; moved the linkage up and solved 90% of the hesitation. As Kern Dog says, the 750's can run lean at WOT, especially with a built motor. I also stepped up the metering rod 2 sizes (which reduces the rod diameter). No more hesitation, car pulls hard.

 

[martin owen]

Did not do this when i first put carb on. Started doing it about week after. I did have a holley 750 on before this, but every one i know convinced me to go with edelbrock, lucky i still have the holly.Could it be a problem with the distributor it looks pretty worn out

 

[dadeo]

Is it electronic ignition or you running points?

 

[martin owen]

Electric it also has a msd6al box, the distriutor is not msd

 

[PurpleBeeper]

OK, just to muddy the water, I will throw in my 2-cents. I say this because you mentioned "new plugs, wires & coils". As tak419 mentioned....it could be as simple as a plug wire boot slipping off the spark plug side. I have had similar issues many times after putting on new plug wires & getting a "mystery, intermittent miss" only to find a plug boot 1/2 on.

Otherwise, it does sound like a fuel issue of some sort.

 

[khryslerkid]

Recheck your plug wires. Had the same problem with them backing off the plugs after a heat cycle or two. Solved the problem when I replaced with "Firecore".

Is your Edelbrock used, rebuilt? The "blue" accelerator pumps are crap. They leak past and won't hold a seal useing ethanol. Replace with the "orange" one, problem solved. (Check into the carb while pulling back on the throttle for a good squirt. If not replace.)

Throw a timing light on her and check for vacuum advance operation.

 

[Ranger16]

I'll second (or third) checking the accelerator pump.

 

[HALIFAXHOPS]

Also check you mechanical advance in the distributor. They never get oiled, Easy check take off the distributor cap and see if the rotor turns and goes back if not it is gummed up. I see it all the time. Just FYI

 

[martin owen]

Put the holley back on and problem solved. No more edlebrock for me