Vac Problem?
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Junior User
Joined: Nov 2000
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From: Birdsboro Good ol' U.S.A.!
Vac Problem?
Hey guys...I put a new Holley 500 on my 351M a few days ago. And things dont seem to be going as good as they should, although the Holley made me swear im never going to run an Autolite again. Engine seems to be advancing quick or something, I mash the peddle and it sorta wants to bog out, or be slow to pick up. Im not talking like accelerator pump woes, im already moving. It feels like a 2 stroke at open throttle then afterwhile hits the powerband and wants to throw you through the back of the cab. Now the Holley I put on didnt have the usual vac hook up for the PCV on the back and I rigged up my own jig and connected it to Mani. vac right where the brake booster hooks up. Also, I hooked the advance up to the carb spacer as I originally had it since I put the truck back together when I bought it, but that seems to pull constant hard vac. Any ideas? Could I be getting too much advance right off the line? I have no other places to hook up vac...wheres the variable cut out or kick on lines? 
It's not what you buy, it's what you build!
1979 F-150 4x4 Shortbed 4 spd 33x12.5's Towing Cam 3" Susp Lift and many other neat thingers
1978 F-150 w/250 front end Supercab 4x4 Dana HD44 Towing cam
1977 F-150 Longbed 4x4 4spd Psycho lift cam, Decked & Bored
1996 Ford Explorer
It's not what you buy, it's what you build!
1979 F-150 4x4 Shortbed 4 spd 33x12.5's Towing Cam 3" Susp Lift and many other neat thingers
1978 F-150 w/250 front end Supercab 4x4 Dana HD44 Towing cam
1977 F-150 Longbed 4x4 4spd Psycho lift cam, Decked & Bored
1996 Ford Explorer
Posting Guru
Joined: Jun 1999
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From: Comox Valley, Canada
Vac Problem?
By the sounds of it you have full advance all the time. I think the advance should be using "ported vaccuum" (meaning you dont get vaccuum til the throttle is opened) rather than direct manifold vaccuum.
I also thought that Holley had a few vac ports, some ported some not. Maybe they are just blanked off from the factory?
Sparky
I also thought that Holley had a few vac ports, some ported some not. Maybe they are just blanked off from the factory?
Sparky
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Joined: Aug 2000
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Vac Problem?
Hi Fordkid. Like Sparky says, change the vacuum advance to a timed port on the carb. You can remove it altogether for testing purposes, the engine will run very well without it (plug the carb port).
I'm not sure about your PCV hookup to the vacuum tree. That may be giving a different vacuum signal than having it under the carb. Try removing it from the manifold, and cap the port. Then take the pcv valve out and let it vent to the atmosphere temporarily, and see how it runs. This might tell you something.....
I'm not sure about your PCV hookup to the vacuum tree. That may be giving a different vacuum signal than having it under the carb. Try removing it from the manifold, and cap the port. Then take the pcv valve out and let it vent to the atmosphere temporarily, and see how it runs. This might tell you something.....
Thread Starter
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Junior User
Joined: Nov 2000
Posts: 95
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From: Birdsboro Good ol' U.S.A.!
Vac Problem?
Thanks for the replies...God I dont wanna say this..Well, what I thought was the vac sec. nipple for the carb was actually my ported vac. It comes out the side of the fuel bowl so it had me thinkin it was secondaries. I didnt have anything hooked to it though so I had me a vac leak there. It seems a little smoother now...hm wonder why? lol. Again, thanks. Somebody shoot me 
:-X11
It's not what you buy, it's what you build!
1979 F-150 4x4 Shortbed 4 spd 351M Mild Cam 33x12.5's 3" Susp Lift and many other neat thingers
1978 F-150 w/250 front end Supercab 4x4 Dana HD44 Towing cam
1977 F-150 Longbed 4x4 4spd Psycho lift cam, Decked & Bored
1996 Ford Explorer
:-X11 It's not what you buy, it's what you build!
1979 F-150 4x4 Shortbed 4 spd 351M Mild Cam 33x12.5's 3" Susp Lift and many other neat thingers
1978 F-150 w/250 front end Supercab 4x4 Dana HD44 Towing cam
1977 F-150 Longbed 4x4 4spd Psycho lift cam, Decked & Bored
1996 Ford Explorer
