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I actually posted this on Facebook and received some possibilities, but I wanted to also get some opinions from you all.
When I set my timing with the vacuum advance plugged/blocked off I was able to get the idle to 800 rpm, which is where I've read it should be close to. Unfortunately as soon as I reconnect the vacuum advance the idle immediately jumps 300 or so rpms. I could not get the idle lower than 1000 rpms; the idle set screw was backed all of the way out/not touching throttle.
The vacuum advance is connected to the nipple on the lower driver's side of the quadrajet which would be ported vacuum.
I'm wondering if my vacuum advance canister is not functioning properly?
Is there anything I am doing wrong or can do differently?
The vacuum advance is connected to the nipple on the lower driver's side of the quadrajet which would be ported vacuum.
If the timing and idle speed changes when you plug the hose in, that isn't ported vacuum, it's manifold vacuum. Ported vacuum will be near zero at idle. Did you put a vacuum gauge on that port to see what the reading is? Also, if the idle speed screw is backed all the way out, you either have a vacuum leak, mis-aligned throttle plates that hold the primaries open, an improperly adjusted fast idle screw of sticking cam, or some other problem that prevents the throttle plates from closing fully.
If the timing and idle speed changes when you plug the hose in, that isn't ported vacuum, it's manifold vacuum. Ported vacuum will be near zero at idle. Did you put a vacuum gauge on that port to see what the reading is? Also, if the idle speed screw is backed all the way out, you either have a vacuum leak, mis-aligned throttle plates that hold the primaries open, an improperly adjusted fast idle screw of sticking cam, or some other problem that prevents the throttle plates from closing fully.
I'll check the reading tonight! I have attached a picture of my quadrajet.
Originally Posted by oldcutlass
If you disconnect the throttle cable/linkage can you adjust it down further and then readjust cable/linkage as required after?
I have not tried that! I will definitely do that tonight, also!
I agree with the above on the likely problem. If the throttle blades are not fully closed, there would be vacuum present at a ported vacuum source and the idle speed screw would not be able to lower the idle below some point.
I suspect the real problem may be a vacuum leak between the Qjet and that E-brock intake. You might need a steel base gasket between them to ensure all the gaps are sealed.
I suspect the real problem may be a vacuum leak between the Qjet and that E-brock intake. You might need a steel base gasket between them to ensure all the gaps are sealed.
That could very well be the issue. Where can I get this gasket?
I suspect the real problem may be a vacuum leak between the Qjet and that E-brock intake. You might need a steel base gasket between them to ensure all the gaps are sealed.
I honestly doubt its a gasket issue because you can get the idle down prior to connecting the vac advance. You can check for a vac leak by spraying some wd40 or carb cleaner around the base of the carb. If the rpms go up you have a leak.
Good news: I figured out that the vacuum advance canister is adjustable so I turned it all of the way down. This allowed me to set the idle (after reaching temp) to 750. Removing and replacing the vacuum advance did not seem, by ear, to change the idle rpm. However when I hooked a vacuum gauge up to the ported vacuum nipple it read 6 hg. So it is still pulling a vacuum at idle.
More good news: The spark plug wire was not fully seated on #8 and fixing that made it ride a little smoother.
Bad news: Besides the vacuum still being pulled at idle, when accelerating (not wot) I may have some detonation. I'm not 100% sure what pinging/detonation sounds like, but the sound I get it could very well be an exhaust leak. The gas in my pickup may actually be close to two years old and I'm sure it is only 87 octane. I will get some new 91 octane gas (highest or goes around here) and some octane boost. Due to this sound possibly being detonation I never went close to WOT.
With the engine fully warmed up, the vacuum advance unhooked, choke fully open, rev the engine to 3000-3500 and set the timing at 34 degrees. Leave the vacuum advance unhooked. Take it for a WOT test drive, listen for detonation. If you don’t hear any, add a couple degrees and take it for another WOT test. If you hear pinging, back off a couple degrees. Once you found the max timing with no pinging, then it’s time to work on the vacuum advance
What Matt said. It will definitely get you up and running quickly.
What kind of distributor do you have?
What cam and rear gears do you have?
Auto or stick?
What is sea level where you live...approximate.
Before you do anything we need to verify the carb and ignition systems are OK and you have zero vacuum leaks.
Verify the vac can holds vacuum.
Read your spark plugs and exhaust tips now and 500 miles from now.
You have to adjust the carb A/F, base timing, vac advance, and centrifugal timing events(points dwell?). They must play nicely together.
You should know what each timing event is doing.
Then you start tweaking each one to dial in the car. Its called super tunning and it takes patience trial and error... We won't get into advanced carb adjustments yet.
You will need an RPM meter, set-back timing light and a vac gauge..which we see you have.
Another method you can try is:
1. Set base timing at 12* at curb idle ~650- 750 ish, no vacuum advance.
2. Set the A/F to achieve the highest vac reading possible.
3. Readjust the timing to get the highest vac reading possible (back n forth etc).
4. Now plug in the vac advance can and see how many more degrees "come in"..at curb idle, straight vacuum source not ported.
5. Set the adjustable canister to bring in 8-10* more at curb idle. Now you are at ~22*
6. With the timing light & RPM meter hooked up give it 2500-3000-3500RPM and see how much more timing the centrifugal advance brings in and at what RPM it stops delivering timing. This is your total.
You're looking for a total of 34-36-38* of timing at 2500-2800-3000 RPM for a tame to mild street 455 on higher octane gas, 91 or better with booster at sea level.
You have to go back and forth with all of this and experiment to find the sweet spot. Give it as much timing as possible without spark knock. Experiment with different base vac and centrifugal settings to see what it likes.
Road test.
Last edited by droldsmorland; March 24th, 2020 at 09:00 PM.
I have never owned a timing light because my father, currently age 92 had always taught me to do the ping test for optimum timing, and a good starting point
He was in the automotive business his entire career. He also said that before timing lights, mechanics used vacuum gauges.
I would pull the carb and make sure your throttle plates are in the correct position and closed enough to pull well from the idle circuit and good vacuum (depending on cam).
And like mentioned earlier, see if you can check your total advance with the counterweights engaged. Hang in there and this will keep you off-the-streets during the Covid spread. I wonder if I have already been exposed.
A timing light isn’t required, trial and error certainly is a option. However, once you have the happy spot it’s nice to know exactly where the initial timing is, that way if the distributor needs to be removed you can reinstall it in the same location.
To the OP, its not pulling 6 vacuum its pulling 2" hg. Instead of adjusting the vac advance down, just disconnect it and plug the line until you get your base timing setup. What timing setting are you using? Did you check for vacuum leaks?
March 24th, 2020, 12:19 PM
