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It will be fuel delivery! either the pump not up to task, or the way the fuel is ran to the carb (s)
Unless the springs have broken the stocker will go past 5500!



I went through this over well over a decade ago, two different sets of MP springs! All crap. Checked the pressures before and after a weeks run time and was horrified how much they dropped off.

Ended up buying a set of battleship steel springs and taking out the inner spring to get the pressure I wanted. Even after years of use still within spec and the motor has been buzzed hard to 7200 RPM.

Before that it would get to around 5000-5500 and pop and frat like it had a bad misfire from a coil of ignition box.

Check the springs, check the springs, check the springs. Really not that hard to pull two and have them checked.

Ignition wise I ended up using a gold NASCAR box, Blaster II coil, and Moroso spiral core 8mm wires all of which made no difference till I changed springs.

Hell I even indexed the distributor rotor with a clear ignition cap and timing light, still got the cap too.


MP springs are junk - you learned the hard way.

Not sure what rockers are on the motor but I had a small block that would break up at 4500. Was running stock non adjustable rockers. Heads and blocked were milled. Hydraulic lifters would pump up at 4500 and cause valve float. Adjustable rockers cured it. I'd start with the valve train - adjustable rockers/valve lash, valve springs, and look at fuel delivery too.