Hey guys, I'm turning this mystery over to this forum after 2 weeks of troubleshooting with no change. I'll try to keep this brief and to the point and provide some details on the build.
340 block +.060, stock forged crank and rods with KB pistons, Oregon Cam solid 572/569. 252/258@50. 106 lobe seperation. Howards oil thru lifters, EQ Magnum heads 1.6 Crane roller rockers. Edlebrock RPM Airgap with Holley 750 dpdf and 1 inch spacer. Ignition is all Mallory, HyFire VI 685, Coil and Comp SS distributor. Accel 8mm wires, Holley blue fuel pump regulated at 7psi. Hooker super comp headers. The car is intended for drag use only, running 93 octane currently.
Problem - at approximately 3000rpm and up, the engine chugs and struggles.
The following changes have been made with no improvement.
Carb rebuilt, jets 72 front and rear. Power valve at 450. Eventantually changed the carb to an 850 from a running car, no change.
Distributor set with 24* mech advance, springs changed to be all in at 2500rpm
Rechecked valve lash .016 Intake .018
Exhaust. A-OK.
Rechecked timing mark with piston stop. Off by 3* remarked with new degree tape.
Disconnected the tachometer.
Made sure the ignition box Rev limiter is set at 6500. Two step is not activated.
Checked firing order, cap and rotor condition.
Adjusted initial timing from 5 to 15 (29 to 39 all in) with no improvement.
Plugs indicate running rich.
I am more then willing to share any more information needed, in exchange for clues that solves this issue.