Holley 750 "stumbles" on WOT
Tough diagnoses only because he claimed no other changes besides changing carbs.
Always begin with correct fuel level.
The jets and accelerator pump inlets are low and at the bottom. However it is possible the fuel level in bowls were low.
Next, check for contact between pump arm and pump cam at idle. This is something that someone could change when adjusting idle speed with the stop screw and not think it was a change. The pump must begin to move when the throttle opens. The 1/10 clearence in the specs is when the throttle is fully open. The clearence at full open is to be sure the spring is not be bound up. It provides some cushion from overtravel.
(Pictures here)
After that I would say check for pump check valve (probably an umbrella type - and these do go bad, especially older ones when used with newer fuels, its not just the eth, its other components too).
Finally, before you set this up for your car (or his) make sure the primary side throttle blades at slow idle are in the acceptable range of .020 - .040" transfer slot showing.
make a note of how many turns or (1/4 turns) of the idle stop screw to reveal .020 and .040 of the transfer slot under the throttle blades. Write that down! Now you have a way to know too much and too little without taking the carb off the intake while turning. :)
Tough diagnoses only because he claimed no other changes besides changing carbs.
Always begin with correct fuel level.
The jets and accelerator pump inlets are low and at the bottom. However it is possible the fuel level in bowls were low.
Next, check for contact between pump arm and pump cam at idle. This is something that someone could change when adjusting idle speed with the stop screw and not think it was a change. The pump must begin to move when the throttle opens. The 1/10 clearence in the specs is when the throttle is fully open. The clearence at full open is to be sure the spring is not be bound up. It provides some cushion from overtravel.
(Pictures here)
After that I would say check for pump check valve (probably an umbrella type - and these do go bad, especially older ones when used with newer fuels, its not just the eth, its other components too).
Finally, before you set this up for your car (or his) make sure the primary side throttle blades at slow idle are in the acceptable range of .020 - .040" transfer slot showing.
make a note of how many turns or (1/4 turns) of the idle stop screw to reveal .020 and .040 of the transfer slot under the throttle blades. Write that down! Now you have a way to know too much and too little without taking the carb off the intake while turning. :)