i have a 750 holley double pumper i will rev a little over six then pops like its to lean took the plug out its white then idle around town took plug out way rich the back power valve is blocked off so i assume i should up jet the back but not sure what do do to the front if i should change the power valve or jets maybe the four corner idle would help any suggestions would be great also when i stom it from an idle it will stumble and quit is i roll on it it a bit first it works fine  

I believe the 4150 750 double-pumper has #76-80 rear main jets when no power valve is used. Are you in this range? Vaccum governs the front power valve cut in-out. Do you know what you engine is pulling for vaccum? What is your primary jet size?  

the rear has 83 main jets i'm not sure of how much vaccum it has its not much i don't think it has a 6.5 valve in the front with 69 jets  

The only way to properly tune a Holley, is to disconnect the secondaries, wire them shut, and tune as a two barrel first. Vaccum needs to be established in order to choose the correct power valve. When vac. drops to a given amount, the power valve opens to enrich the the fuel delivery. The primary jets, from the factory are 71-74. Give me the carb # located on the airhorn, and I will give you the factory specs. Start there. They are never far from the mark.