another one - quick vac advance question
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Junior User
Joined: Jan 2014
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another one - quick vac advance question
79 351 edelbrock 4bbl w/ holley 600 and factory distributor w/ hose from timed port at top of carb. runs smooth as a ribbon without v/a unhooked from off idle and at cruise. when I hook it up no at idle issue but when I accelerate and vacuum comes in it stumbles or / misses like crazy - the more I accelerate the more obvious it is. sounds like I have plug wires pulled off. block off v/a and it runs great. do need v/a however because it is street driven. timing is at 12
any advise would be appreciated.
thanks
any advise would be appreciated.
thanks
More Turbo
Joined: Oct 2006
Posts: 632
Likes: 40
You will likely get differing opinions, but in my experience for a street driven (non race) vehicle ported vac advance improves off idle and light throttle responsiveness. No idea what is causing your issue. I did have a GM HEI that did exactly what you seem to be describing. Drove me nuts till I figured it out. Reman dist was defective and somehow shorted internally ONLY when vac advance moved. Idle was fine, as was heavy throttle. Just an idea. Good luck
Lead Driver
Joined: Feb 2002
Posts: 7,960
Likes: 594
From: Greater Austin, Texas
This means the bushings in your distributor are worn out. When the vacuum advance pulls on the breaker plate in the distributor, the worn bushings are allowing it to get out of kilter (i.e. not centered).
Postmaster
Joined: Mar 2011
Posts: 2,698
Likes: 7
From: Taxachusetts
Oh, yeah...there's a bunch of reasons. My bet is the vacuum advance diaphragm is shot - torn, a hole in it, etc. That lets air into the ported nipple on the carb when called for an advance.
Suck on the tube - if you get nothing but a good breath, there you go.
Your wires inside the old distributor vacuum plate could be too brittle to move...shorting out.....if the vac advance works when needed.
Suck on the tube - if you get nothing but a good breath, there you go.
Your wires inside the old distributor vacuum plate could be too brittle to move...shorting out.....if the vac advance works when needed.
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