Quardajet Vacuum Lines - Pontiac GTO Forum
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post #1 of 6 (permalink) Old 11-05-2017, 03:51 PM Thread Starter
 
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Quardajet Vacuum Lines

Today I pulled the old Holley off of the car and installed the new Jet Stage 1 Quadrajet. Along with the carb I put on a 1" spacer, also from Jet. Installation went pretty much as planned, except the new fuel line was very difficult to get in - I had to do a little bending to get it lined up and threaded right on the top and bottom.

With the carb torqued down and the new fuel line in place, I found that the throttle linkage is a lot different - I'll have to play with a new spring set or buy a new kit, we'll see.

When I went to plug back up the vacuum lines I found myself scratching my head - there are a bunch of ports on this thing and I could not find a diagram anywhere for what is what.

I scoured the interwebs and referred to my shop manual but couldn't find anything that looks like my carb.

So I figured I'd take a picture of it and ask you guys for help.

Here's a quick video of what I have and what's set up. Sorry about the lighting, but I have everything all buttoned up for the day, so I was on flashlight. See:

First time I've ever done this, so pardon the newbie questions!!

I'm looking to find out where to put each of vacuum advance line, vacuum line to transmission, and the brake booster.

Note that I did start it once and it was very rough - wouldn't run without working the throttle. I ran out of time for the day, so that's where I finished...not sure if it just needs some air/fuel mix and idle tweaks or if I have my vacuum line placement jacked up. :-)

Thanks for any guidance!
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post #2 of 6 (permalink) Old 11-05-2017, 07:06 PM
 
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Should be able to use a factory gas pedal cable, bracket, and return spring.

Brake booster hose typically hooks in the back of the carb. PCV valve hose hooks in the front.

Simple way to test the vacuum ports: To test the vacuum ports off your carb is as simple as starting the engine, let it idle and pull the hose off the port. If you have vacuum at the port (put your finger to the port and feel for suction and the idle should change if there is suction) when idling it's a manifold source. If there is no vacuum at idle, crack the throttle a bit and feel for vacuum at the port. A ported source will start sucking as the rpm increases and the throttle plates open up. Of course you could buy a vacuum gauge and hook it up to find out as well.

Finding a pic on the web matching closely your carb, the fitting above the fuel filter inlet with gray cap is ported. The port on the right (drivers side) should be manifold vacuum.

Bases on the Q-jet can be different based on year/make, so you may not even have a port at the rear for your brake booster. I see a plug in your intake. You can tap off this with a T-fitting to get your manifold vacuum for the brakes, trans, & distributor ( if you run manifold vacuum to it). Something like this: https://www.summitracing.com/parts/c...yABEgKmdPD_BwE So you have options.
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post #3 of 6 (permalink) Old 11-05-2017, 08:11 PM Thread Starter
 
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Hey PJ - Thanks as always!

- On the factory throttle cable, bracket and return spring... The throttle cable has definitely been replaced - it has some ungodly mix of nuts and washers on the end - not my doing! I tried using the one the guy before me had, but the spring is stretched way too far. There's also a kink in the cable that hung up on me once while testing WOT and kinda scared me for a sec...so I think a new throttle cable is in order.

- As it turns out, my engine vacuum gauge is not working - dang thing is hung up, so I can't use it. Funny - ran down to Advanced Auto Parts to see if I could get a new one and the kid at the counter gave me the deer in headlights look. Is a vacuum gauge really that crazy of a thing to want?? Maybe just a dumb kid.

- You mentioned a plug on my intake - on the intake manifold there are two plugs right there on top - one right next (left side) to the radiator hose and another on the right side (drivers) just in front of the right front corner of the carb. To which one were you referring? That sounds like an easy fix - use that for the brake and transmission, and the ported vac on front/top/left (gray cap) for advance. I'm just not sure which of the plugs on the intake manifold is the right one to remove and tap with that mentioned T Fitting.

Now it gets dark at 5:30. Looks like tomorrow nights ruined getting some decent lighting in my garage.... :-)
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post #4 of 6 (permalink) Old 11-06-2017, 06:35 PM Thread Starter
 
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The solution to the brake vacuum was found in the rear center - I'm not sure why, but Jet left that vacuum port (rear/center/manifold) open, with no fitting/hose barb on it. It was just an open hole. The fittings evidently don't exist at the local auto parts stores either, but Lowes had one.

So, threaded the fitting in and popped the brake booster on there and it works great.

The other two are what I first thought - the bottom front is manifold and I have the trans attached there, and the upper right side is ported.

Just a short time ago I started it up again (after first try yesterday) and what a huge difference! Funny how actually having a functional choke makes things better.

Fast idle is good, but a little slow after it warms up, and Drive drops the RPM's to 550-600 - almost cutting off. That's with NO adjustments. And...no more burning eyes fuel vapors and best of all, no dripping gasoline all over the manifold. :-)

Yesterday the first start up was a bit rough. I only had it on for about a minute and it was really rough. I'm assuming that's because I had the fuel line off and drained all the gas out of the fuel pump and line - I was thinking that'd cause some rough running until the fuel system was primed again. I can't think of another reason why it'd run crappy yesterday and find today, since the vacuum lines are the same (except brake). Thoughts on that?

So now.... Plugs, wires, timing (again just to be sure), fuel/air and idle.

Then, on to the boxes of exhaust parts on my garage floor....
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post #5 of 6 (permalink) Old 11-06-2017, 07:14 PM
 
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The rear center is where the brake hose typically goes. Yes, it is a threaded hole and you can use a straight line fitting like it sounds you did. Some factory carbs will have a fitting with a large outlet for the brake hose with several smaller fittings for various other vacuum lines.

The engine runs better BECAUSE the hole in the back of the carb was sucking air and not sealed off.

Just make sure your transmission line is hooked to the manifold vacuum line and not ported.

On the distributor, many opinions on ported or manifold vacuum. You can play around with it to see what works best. Always set your initial timing at the balancer with the vacuum line to the dist. disconnected and blocked off. If you choose to try manifold vacuum, as soon as you hook it up, it will advance your initial timing at the balancer. You initial timing (which I believe is 9 degrees) will be your setting with the line disconnected PLUS what the vacuum advance pulls - so it will jump up to over 20 degrees. Often the engine will run better and smoother. So keep this in mind as I think you said your timing was already at 15 degrees? I don't know if this is with manifold vacuum or ported.

You are probably going to have to adjust the idle up a little and you might want to adjust the idle mixture screws and dial them in. I think you are going to really like the Q-jet and the sound when you pop it open.
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post #6 of 6 (permalink) Old 11-06-2017, 07:54 PM Thread Starter
 
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Yep - just like you mentioned, just a simple straight fitting is all it needed.

When I did the last timing tune I used ported vacuum to the distributor. That seemed to really do nicely. That made total advance @ 35 and initial timing at 15 degrees. I drove like that for an afternoon and it seemed to do really well, though I'm not convinced it's as dialed in as it could be. Since the carb is new since then, I want to go through the entire procedure again.

Here's the idle - again, no adjustments at all, just right out of the box. Needs tuning for sure, but not terrible... See:
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