Cliff's Quadrajet Parts and Rebuild Kits

General Category => Quadrajet Carb Talk and Tips => Topic started by: Shark Racer on February 23, 2014, 04:52:28 PM

Title: Is the distributor port supposed to be ported vac?
Post by: Shark Racer on February 23, 2014, 04:52:28 PM

(http://elucidus.smugmug.com/photos/i-rDZKfm9/0/M/i-rDZKfm9-M.jpg)

I'm using this port, which IIRC is supposed to be a ported vac source and meant for the distributor. The car is a 78 and this is a 17058228 carburetor.

Testing with a vacuum gauge shows this to be a manifold vac source.

Title: Re: Is the distributor port supposed to be ported vac?
Post by: Ethan1 on February 23, 2014, 06:02:07 PM

 Not sure, Steve. That should definitely be the port for ported vacuum. Let see what Cliff says.

Title: Re: Is the distributor port supposed to be ported vac?
Post by: blazer74 on February 23, 2014, 08:44:31 PM

That port is full vac on my 17056228 , 17057204 carbs.
Lower right (pass side) on base plate on my carbs  is ported vac.

Some carbs have a bleed off  that reduces vac at higher throttle blade Openings to some ports.

Title: Re: Is the distributor port supposed to be ported vac?
Post by: Shark Racer on February 23, 2014, 09:55:00 PM

Quote from: blazer74 on February 23, 2014, 08:44:31 PM

That port is full vac on my 17056228 , 17057204 carbs.
Lower right (pass side) on base plate on my carbs  is ported vac.

Some carbs have a bleed off  that reduces vac at higher throttle blade Openings to some ports.

Yup, EGR is hooked to the lower right port on my carb. I tested that as well, and it takes quite a bit of throttle angle for it to be engaged.

Title: Re: Is the distributor port supposed to be ported vac?
Post by: Cliff Ruggles on February 26, 2014, 04:57:59 AM

That is the correct distributor port on most q-jets.  A few part number in the mid-1970's will be manifold vacuum at that port, then again in the early to mid-1980's.  The vast majority will have ported vacuum at that location.

Almost all of the ported options in the baseplate will either have a high source location, or a bleed off "slot" to lower the signal to the EGR valve so it doesn't lean out the engine and cause running issues.  None of these ports are suitable for the vacuum advance without some minor modifications.....Cliff

Title: Re: Is the distributor port supposed to be ported vac?
Post by: Shark Racer on February 26, 2014, 09:19:32 AM

Quote from: Cliff Ruggles on February 26, 2014, 04:57:59 AM

That is the correct distributor port on most q-jets.  A few part number in the mid-1970's will be manifold vacuum at that port, then again in the early to mid-1980's.  The vast majority will have ported vacuum at that location.

Almost all of the ported options in the baseplate will either have a high source location, or a bleed off "slot" to lower the signal to the EGR valve so it doesn't lean out the engine and cause running issues.  None of these ports are suitable for the vacuum advance without some minor modifications.....Cliff

Hi Cliff - does the baseplate determine whether or not that port is manifold or the body itself?

Thanks to everyone for the help. :)

Title: Re: Is the distributor port supposed to be ported vac?
Post by: Cliff Ruggles on March 15, 2014, 04:17:36 AM

The source location in the baseplate will determine if the port has manifold or ported vacuum at idle speed.  Off idle both will show full manifold vacuum.....Cliff