carb help

stock 460 770 truck avenger in 4x4 truck 4 speed.. idles , runs great, no stumble from idle drives good until u open it up ... once the secondaries open it revs up for a just second then stummbles hesitates until throttle is let up then it smooths out runs fine. Won't run at wide open throttle driving, but will rev up just fine sitting.

New diaphragm in secondaries , changed power valve, carb was rebuilt ran great on my other motor . silver spring. Dont find any vacuum leaks

only thing that was changed was the carb to spacer gasket. This is the stock 4 hole non egr spacer my old one was thicker and had 4 holes same size,, the replacement is thinner and the 2 holes has a cut out between them in the center could this be the problem?

Thanks

have you checked and seen if it is running out of gas

Hey there! Um no i have not i was wondering if the fuel pump was not pumping enough to keep up? This is a new truck i just got so im trying to work out all the bugs! It ran ok before but the secondaries wouldn't open so i replaced the diaphragm and they seem to be working now but it won't run long with it open. Now this new worse hesitation that wasn't there before. So i guess if the secondaries were not opening before it wasnt to bad now with them opening it is running out of fuel?

It had a slight stumble before under a load but not this bad. It all but quits.

Checked for vacuum leaks?