Trying to help my B.I.L. with his 455 mid range stumble during acceleration.
Honestly I'm not in my comfort zone so I thought I'd ask for guidance here.
More honesty....... Its a Buick. Hope the basics apply.(I would think so)

Its unknown year, unknown cam (previous owner said RV?-not much help)
It has a newly redone Q-jet and distributor was rather worn but has been rebuilt.

Here is the issue: Pulls strong low end, pops (backfire?) mid range then clears and pulls like a freight train.

Did it before and after distributor re-work.
Had a Edelbrock carb before the Q-jet and may have gotten worse w/ Q-jet.

I've spent very little time in the car. Wish I had more info.
Just need ideas for places to check or likely culprits.

I'm thinking timing check, and look for vac. leaks. Right track?

Maybe pretend its an Olds I really don't want to sign up to another forum.

Thanks in advance!

 

Definitely do those, but the problem sounds to me like you may be a bit lean in the primaries - maybe larger primary jets or smaller primary needles, or maybe the spring on the power piston isn't strong enough and the needles are staying too far down for that vacuum level.

I'm sure others will have other ideas.

- Eric

 

Thanks Eric, I have Cliff's Q-jet book and figured I'd have a look and see if it has a section on run ability. Also just found he has a forum.
Worth looking at. http://cliffshighperformance.com/sim...hp?topic=731.0

 

It could be the carb, it could be the distributor. It could be the wiring to the distributor, it could be a bad spark plug or wire. It could be ...? Do the basics and start with checking the tuneup specs.

 

Spent a small amount of time checking over the Buick Saturday.
Didn't get to go through the complete check of everything we wanted to.
What we did find the timing was past 12* we backed it down to 10*
In doing so we noticed erratic timing. It seemed to be steady then bounce around like a loose chain would cause.
If the chain is loose would it not bounce always?
Anything else cause erratic timing?
Also if the chain is loose would that cause it to fall on its face @ 2500
under load. It was at 3500 a couple times also.
Revved well w/o issue parked so load seems to be a factor.

Pulled strong after the stumble which to me would rule out ignition wires,
fuel starvation as those wouldn't clear up till RPM's came down. Right?