I have fought a Holley 750 DP for 2 months trying to figure out this problem. I have put 3 different sets of needles and seats on the primary and secondary side (almost everytime it happens which is alot it pours out of the primary side) my fuel pressure is 7 PSI i have lowered it all the way down to almost 4 psi trying to prevent this problem with no good outcome. I have replaced both float bowls and have even adjusted them almost all the way down and this problem is still happening. I am constantly fighting this carb i'm about to throw it in the trash. The carb is on a 408 CI sbc 12 degrees of initial timing and it swings out to 34 the vacuum advance is not hooked up. Any info will be greatly appreciated!!!!!!!
Well carburetors are generally meant to only run it maybe two PSI I would lower the pressure even further but if it's still does then they sold you a crappy carburetor
Your floats might be ok but have you checked your float needles and float needle seats? They may be damaged.
I've had really poor luck with Holley carbs...I can't give you any advice because anytime I worked on them they leaked more. If possible I would get an Edelbrock. I've had great luck with Edelbrock carbs, and when I've installed them for the most part it was install and go. Some tinkering sometimes but not much and nothing major.
