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Quadrajet vacuum ports, distributor advance Q

fidelity101

fidelity101

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I am hearing and reading lots of mixed answers for this question.

Basically I am trying to find the right port to use for my distributor.

or1e.jpg

This is what I'm assuming

1 = brake booster line

2 = to distrubtor?

3 = ???

4 = EGR

please correct me if I am wrong, I did not label the big PCV hose because I was 100% certain I knew where that one went :) :whistle:
 
Based on the way things are setup in that picture now, are you just trying to make it run good vs. meet a visual or tailpipe inspection/sniff test?

If so, hook the distributor up to a manifold (vacuum at all times) port, whether on the intake or at the carb, and see how it likes it.

You will get all sorts of varying opinions, however, ported vacuum is an emissions control device. If you aren't concerned with emissions, and the engine likes it, run manifold vacuum. You give the engine the timing it wants (how it runs best), not what you think it wants.
 
I think base timing on most small blocks tends to be around 8*, if yours is set around there, hook it up to manifold vacuum and see how it runs. You've got factors like how it starts to consider as well...too much timing and you will hear/feel how much harder the starter is working than it needs to.

Vac advance is there to apply advance under LOW load conditions. Manifold vacuum drops under acceleration, so it is a non-factor except at idle and cruise, which is where additional advance helps markedly. As soon as you hook the vac advance up to manifold vacuum, idle should pick up and smooth out, acceleration should be unaffected.

There are a variety of vac advance cans out there, so how much advance yours pulls at X vacuum is an unknown at this point. But you can easily check with a timing light if your timing tab is easy to see...check timing with vac advance unplugged, plug it in, check timing again, at least at idle, that's how much advance it pulls.

FWIW, fuel injected vehicles run 20+* of advance at idle. Getting that high with mechanical and vacuum advance, and still being able to crank the motor easily is probably unrealistic.
 
blaznjon said:
the brake booster is the threaded connection on the base plate.try this for the rest. it looks like about a 1977 truck q jet to me.

http://www.google.com/imgres?imgurl=http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/1d/b2/b0/medium/0900c152801db2b0.gif&imgrefurl=http://www.autozone.com/autozone/repairinfo/repairguide/repairGuideContent.jsp?pageId%3D0900c152801db29f&h=392&w=500&sz=40&tbnid=1Cd45-Tr6SOgCM:&tbnh=85&tbnw=109&zoom=1&usg=__yKZMtclZ3TJLF-TfkOH0jmx40fs=&docid=x21fiH7s7W8KZM&sa=X&ei=ruPeUevIG6SviAKEqYHgBQ&ved=0CDcQ9QEwAg&dur=16441
Click to expand...


Yeah I'm not concerned about the brake boosted. I did see that threaded connection and I plugged it, along with the one above it. Vehicle is equipped with hydroboost. I'm not exactly sure what year/vehicle this came off of. I'm only certain that it is a chevy because of the passenger side fuel inlet.

This was last used on some camaro (I believe), I got this carb from a friend of mine, I'd ask him but he's on vacation and usually hard to get ahold of as it is... I recieved the carb with that bolt in the hose plugging that hole, I assume he must have had some fancy valve cover breathers on it then.
 
i would use the pcv port and one pcv valve on the drivers side you can put a breather or run a tube to the air cleaner on the passenger side.

reason being carb will likely run rich with out the extra air the pcv valve lets into the base plate. you also have a good chance of oil leaks if used the way you have it.pcv valves are one way and having two one in each valve cover is like sealing both valve covers.you need to get rid of the normal blow by or it will find its own way out.

you can check the serial numbers on the carb and find the year and application it came from.
 
blaznjon said:
i would use the pcv port and one pcv valve on the drivers side you can put a breather or run a tube to the air cleaner on the passenger side.

reason being carb will likely run rich with out the extra air the pcv valve lets into the base plate. you also have a good chance of oil leaks if used the way you have it.pcv valves are one way and having two one in each valve cover is like sealing both valve covers.you need to get rid of the normal blow by or it will find its own way out.

you can check the serial numbers on the carb and find the year and application it came from.
Click to expand...
I cannot run a line to the stock air cleaner because I don't have one :(

I have a holly freflo, I don't like it but it is what I have available right now.

I tried that originally but I cannot find valve cover breathers for the life of me! All of the diameters are too large for these and I can run a ford PCV elbow (autozone special) from the grommet but I cannot find a universal small cone filter to stick onto it. The running rich via the extra air in the baseplate makes sense because it seems to have a high idle.

Where on the carb would I find the serial numbers?
 
You should be able to shove the stock "bowtie" breather filter from the air cleaner housing into the valve cover grommet on the passenger side,and run the PCV valve on the drivers side cover--or get a oil filler cap with the breather made into it...some also have provision for a PCV valve in them too..
 
Carb numbers are (as looking at that photo) on the vertical portion of the carb near the back, right side as I recall, next to the short bolt that holds it to the intake? Been a few years since I looked.

Stock air cleaner should be cheap/easy to find, if you wanted one. I suppose you could at least use the filter element that is supposed to go inside the air cleaner on the hose, the fitting is part of the filter element.
 
I use ported for dizzy, like was said prior vac drops off when u hit the gas and mechanical adv take over utill u let off the gas or reach cruise speed and vac stabilizes and vac adv is added again.
Unless u need extra timing at idle do to compression, big cam etc u don't need full vac at idle for dizzy. It all depends on what works best for your engine.
Some quadrajet also have timed ports that have reduced vac to them and don't work well for vac adv.
 
dyeager535 said:
Carb numbers are (as looking at that photo) on the vertical portion of the carb near the back, right side as I recall, next to the short bolt that holds it to the intake? Been a few years since I looked.

Stock air cleaner should be cheap/easy to find, if you wanted one. I suppose you could at least use the filter element that is supposed to go inside the air cleaner on the hose, the fitting is part of the filter element.
Click to expand...

Like so?

7mfb.jpg


top# 1705920 5
bottom# 0579 CBD

with a quick google search it looks to be an manual transmission march of 1979 carb for any GM/pontiac/chevy vehicle 4 barrel.
 
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