Help me find manifold vacuum at the carb...

[243]

I am working on the 4bbl Motorcraft carb that came on the 401. I would like to hook up a vacuum gauge to set the idle mixture but can't find manifold vacuum, found ported but won't help.

I found two ports, both on the front corners and neither pulls a constant vacuum.

Thanks,

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243

Ol'e Blue
79 Wagoneer 401/T400/QT

http://www.0hassleisp.com/dwilk/79sig2.jpg

Red 75 Wagoneer (project)
Mean Green 76 Wagoneer (parts car)
99 Dodge Ram TD

cummins_isb@hotmail.com

[joe]

You need ported vac to set the mix screws.
Plug the vac gauge in at the dist vac advance hose "after" it's good and warmed up. You won't need to have the dist vac adv operative at idle when warmed up. Just remember to hook it back up when you're done http://www.ifsja.org/ubb/smile.gif

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Regards,
-joe
63 2-dr Wag, 72 J-4000, 73 J-4000, 82 CJ-8

[243]

Joe,

Is "ported" constant, the same as I would find right off the manifold?

If it is, I am using the wrong terminology...

I am getting a pretty steady reading of 19.5/20.0hg the way it's sitting right now.

243

[joe]

You're reading manifold vac there and neither man or ported is constant under acceleration/load. Manifold vac drops as the throttle increases and ported vac increases as the throttle opens.
On the later FSJ's the vac advance runs off both manifold and ported vac via the CTO. The CTO adds man vac to advance the timing a bit to add in warm up soothness. At 165 deg water temp it swithes to ported vac for driving use.

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Regards,
-joe
63 2-dr Wag, 72 J-4000, 73 J-4000, 82 CJ-8

[nograin]

At Idle, Ported sources will read zero.
Manifold sources will read between 16-19"Hg

There may be no manifold source on the carb itself (like the 2150s). If would be a port near the base if there was. Follow the hoses from the TAC system in the aircleaner and you should find they usually go to a facume fitting in one of the intake manifld runners. With the aircleaner off, you got to plug it anyway so its a good place to hook up the vacuum gage. Another place sometimes is the PCV valve if it has the T in it to the charcoal canister. That T is ususally a strong Manifold vac source.

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360 727auto-trany, NP229
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