Engine Popping
 

Ive got ann 88 RCSB that originally came with TBI. In August of 2009 we swapped it out and put heads, intake, cam, and carb on the 350. Truck ran good then the fuel pump went out. Replaced fuel pump with an edelbrock 255 gph (went big for big block motor coming soon). The day we put the new fuel pump in the truck has started popping at cruising speeds. Changed plug, plug wires, checked for vaccum leaks and checked timing. Pulled plugs out and they were very black so truck is running rich. At WOT the truck runs PERFECT, but as soon as I get down to cruising speed where gas pedal is hardly pressed it starts popping out the exhaust. Fuel pressure is 6 PSI and timing is 32 degrees. Please help this is driving me CRAZY.

Any mods on the carb?

Unburnt fuel getting ignited in the exhaust? and it happened right after replacing the fuel pump? Do you have a fuel pressure gauge on there somewhere so you're sure that the pressure is at 6 psi?

There are no mods to the carb and I have a fuel pressure gauge mounted on the fuel pressure regulator. Before we replaced the stock fuel pump the truck ran great, but as soon as we put in the new one it started this popping. As long as your at WOT or accelerating it doesnt do it, but when I start to let the truck cruise it starts popping or misfiring really bad.