Missfires

[1990Obscammed]

Hey guys I've been building my obs for some time now, it's a 1990 Scottsdale, I ditched the tbi system and put a set of Corvette heads on with a comp cam with 468 lift a wiend intake and a 600cfm Holley carb, now I have tried absolutely everything to fix this problem but I can't seem to figure it out the thing starts right up and runs like a top, driving it down the road normal it seems just fine but when I punch it once it gets up to 4k rpm it will start stuttering and skipping really bad and as you hold it to the floor it will slowly creep up to 5k rpm, ive tried everything I can think of and I've been doing weeks of research anything will help (p.s. I'm only 21 Im not the best with this old school stuff, also it's a five speed manual if that matters) thanks guys!

 

[Schurkey]

Perhaps a moderator will move this to LSX + Carb Swaps.

What is the fuel pressure when the engine loses power?

How is the distributor centrifugal advance curved? Where is the vacuum advance connected--manifold vacuum or ported vacuum?

Have you measured exhaust back-pressure? Are any of the exhaust pipes crushed? Catalyst plugged? I've seen double-wall exhaust pipes where the inner wall collapsed but the outer wall looked fine. I don't know if these trucks came with double-wall pipe, but replacement pipes might have been double-wall.

Are the valve springs suitable for the camshaft? Did you verify no coil bind at full lift, retainer-to-rocker clearance, retainer-to-valve stem seal clearance?