[Chevy 70 SS vert]

I started the 454 70 chevelle yesterday and took it out for a spin since it was a really nice day here. Started with little or no trouble. Warmed it up with the usual driveabilty issues. After it warmed up I started noticing a miss on light acceleration. Yet under full acceleration it pulls fine with out a miss. Carb is still wired to only open up with the 2-barrel operation until I get a few more miles on the engine. So performance isn't stellar. After diagnosing it I found the vacuum advance would not hold a vacuum on the diaphragm. So I need a new one of those. Yet I doubt it would cause a miss on light acceleration. I plugged the vacuum line going to the vacuum advance to see if it would change. No change noticed.

Spec's are as follows:

468 cu in .060 over 454
Roller cam .512" lift 230 duration.
Quadra jet carb professionally redone by a Quadrajet specialist (who I believe knows what he is doing).
Stock distributor with a pertronix Hal effect/pertronix coil.
New wires
New AC delco plugs
New Dist cap.
Stock exhaust Manifolds
10:1 with dome pistons, running premium fuel.
Heavily reworked 781 heads, ported and polished, bowl blended.
4 spd Muncie 3.08 gears


Any ideas what could be cau
sing my light acceleration miss?

 

[72convertibless454]

bump

did you ever figure this out? I have the same exact problem and very similar engine combination.

 

[p-hanny]

a plug or wire or hair-line arcing in cap can give you that sensation and you dont feel it under heavy throttle (normally you will but NOT always). If all these parts are new or OK look at a possible vacuum leak as well would give you that,,,,, under heavy acceleration vacuum leaks dont matter towards a miss. An intake leaking gasket for instance would give you that exact misfire. Good luck

 

[Chevy 70 SS vert]

Yep, I put on a new distributor vacuum can and it solved the problem!

 

[72convertibless454]

for me, I put a new carb and the problem went away.