Im having the same problem as of yesterday. The reson I found this thread.

Same thing happing to me. I had a 125 power shot on my car and the thing ran fine. But now I went to a 2 stage setup Im nosing at about 5000rpm. I also thought of a fuel problem so I installed a fuel cell and two fuel systems. Both running holley blue pumps threw 1/2 inch tubbing. Pressure is at 7lbs. Also installed a fuel pressure gauge and seems to be constant pressure. Im only using one side of that 2 stage at this time till this is fixed. Funny think is the only thing I did was take 2 degrees of timing out of the car and bolt on the new plate. I also in a 1/4 mile run melted off all ground straps on the plugs. Took the car last night to a 1/8 mile track and same thing happens nose dives and breaks up at 5000 however first gear seems fine 1.51 60 footers , But as soon as second gear comes blllllahhhh blllllahhh nose dives. Heres what Im going to do...

New carb tomarrow...holley 750 HP! I also went out today and bought a NOS delay box and a 4 step MSD retard box. Im running two colder then stock spark plugs. Going to 3 colder.

Again the wierd part is I only sliped a new plate under the carb. Sheesh making me nuts.

Have you had any luck fixing your problem?

PS...Great forum everyone...I'll be around more.