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quadrajet: the fuel pump, fuel bowl, and accelerator pump

Ha! Must be something that was common. Buddy had a '73 that came to him in a roundabout fashion, that think probably weight 1/2 again as much due to the extra welded on stuff for hitches!

Too bad there isn't an easy way to even temporarily run a return line. I suppose anyone that has one of these trucks and an IR temp gun can try what you have done, but not sure many will be that interested. :( Besides, I'm a big fan of keeping it consistent, and your setup will show different temps than another setup.
 
I have the 'no return' case study anchored.

Today I did a few things:
- 1" 4-hole wood spacer - lost a bit of off idle bottom end, had to watch backing up hill out of driveway so not stall, bottom of carb is now 100 deg F (was 200 deg F)
- EDIT: propane leak test @ carb base and throttle shaft, no change in idle, example video
- tested spark plug wire resistance - all good @ 50 ohm/ft
- adjusted choke to 'warm' (dot #2) setting, fast idle now comes off
- tuned idle circuit to high vacuum (20 in-hg)
- removed dummy airhose (controlled vacuum leak) - idle needles nearly bottomed out
- gave the secondary air valve spring an eighth turn tighter, no bog on flooring it.

I have a 1" phenolic 4-hole spacer in the mail, should have gone with 1/2", dont know till you try.

Also ordered a fuel pressure gauge and t splice. Plan to check fuel pressure and see if that could be a hidden cruising problem. Seems fine but by the numbers it is close one way or the other. If over 5psi then pressure regulator is next.

The choke seems like it is not doing what it should. I sat there and watched it and it never moved. So, I adjusted it open. The pull of dosent even touch it on startup. I checked grounding and it is fine. Might buy three elec choke from three mfg and test all three.

I will drive it like this for awhile and see if it is livable.

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Your cruise issue may be the fact your idle circuit is so lean.. Try opening them a bit and that may also give some of that low end back. Usually I would add more initial timing for this but if try both.. Initial on a sbc can be as high as 25 degrees before its a diminishing return but you have to limit the mech advance
 
Run it a little rich, OK. After I run a tank and get the gas milage, I will give that a try.

The timing should be on the upper end. I might be able to get some more. I've never heard about limiting the mechanical advance. What is the purpose and how is it done?

EDIT: I found this site http://www.crankshaftcoalition.com/wiki/Hot_rodding_the_HEI_distributor

Is there a hei tuning thread you recommend on ck5?
 
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Think of it this way the engine will be more responsive with more timing advance, you give the engine longer by lighting the mixture sooner and because the heads these come with stock suck and are super slow burn this make a huge difference in low end tq. The point of limiting mechanical advance is so you don't have too much timing because the max for most sbc is 38-40 and crusing around 50 but that depends on what your engine can handle. There is a ton of info on the internet regarding this.
I can tell you from my testing it will be the biggest change power wise you will feel aside bolting on carb and manifold. If you have any questions just ask.
 
I know what you are talking about, it makes a huge difference. I set the timing, take it out and then floor it. If it pings, then I turn it back a bit, if not I give it some more advance. After a few trial and error runs it is dialed in. Mechanics hate it when I tell them that. I have no clue what my advance is, but I know I can't have any more.

Using that approach I found a few things that in retrospect are obvious:
- if the engine gets hot, you can't run as much timing, holding the temp at a set point is really important. I can't run as much becuase my cooling is not that great, in the summer my temps can climb to 210 deg F. That limits what I can get from advance.

- Obviously, octane is a big factor. Put is high octane and pull the timing up but it cost you in fuel. I use 87 so I can't run as much advance.

- A lean tune will ping easily. A rich mix is more forgiving and allows for more advance.

- The worst is when I have 87 octane and running a lean mix trying to save gas. It gets to a hot day, I go up a grade, and it starts to ping a little bit, but, that shoots the engine temps up and with marginal cooling it quickly overwhelms the cooling and next thing you know I am nearing 215 deg F. At that, my tune is done and all it does is ping if I touch the gas. Complete runaway reaction. I'd have to stop, dial back my timing, richen the mix a bit, and let it cool down. I leave a little fat between my advance and the ping.


I read in that link I posted that you can 'find' a midrange ping that limits your advance. With some curve adjustments that midrange ping can be eliminated and open up for more advance. I'd bet that is what I was running into.
 
What mostly your referring to is the vaccum advance and because some of the advance canisters add like 20 degrees of course it's gonna ping, at cruise the mech and vaccum are added together so check this out.
Base timing 20 initial
Mechanical timing 18 all in @2500
And vaccum 12 @10hg
What at means is under full throttle you will have 38 but under a no load scenario you have 50

You can limit both to suit your engine and doing this will allow you to run a leaner mixture and will get better Mileage and run cooler. It will take time so find this because of testing but it will pay for itself. The engine will be a lot happier and will run better overall. All the things you stated are mostly myths because people don't understand what's going on and will tell you old school anecdotes to suffice for facts and real world testing.
 
This is not hard to change and make work for your truck, all you need is an adjustable timing light a set of advance weights and springs 8 bucks from summit or junkyard surfing. Time, the ability to make good notes and more time :) a wideband helps a lot with mixture but it's only part of the puzzle
 
Ol school pramatism - sometimes it just works


I will look into a timing light and play around with the timing. I have a GM performance HEI from 1995. I dont know much more about it.

On a side note, my wife likes the 1" spacer, it quieted the engine noise in the cab. She no longer has to yell for me to hear her.

The morning it didn't start right up, mybe two or the revolutions before it fired. Livable but something different.
 
You will find the taller manifolds will do that I think it's because there is more airspace so the mixture to start has to be richer. At least that's what I have found in my testing , try closing the choke a little more that should help a bit. And your hei may have adjustments built in. If your vaccum adv has flat edges like a large bolt it most likely has an adjustable diaphragm
 
The choke is difficult to get right - I had it closed more and the fast idle never wanted to come off. I turned it back and it comes off fast idle just right. I will close it a little bit and see how that is.

It drove really nice today. I like this spacer. After a 1.5 hour meeting it started right up, I didn't press the gas, just got in and pushed the ignition. It idled a little slow at first - 525rpm - then was fine.

Once during the drive, after leaving the meeting when it was still warming back up, out of the stoplight it felt a little sluggish getting going off idle and could have stalled if I didn't feather the clutch. Hopefully richening the mix and some timing tune will resolve that.
 
Solution:
My hard start when warm problem is gone. I'd like to have fast idle for a short time when warm, but it seems like the accelerator pump squirt floods the engine. That is what I am going off right now as a working theory.


  • How to start a warm quadrajet (less than 4 hours since last started in warmer weather). Do not press the gas, just start it up, if it idles low and wants to die, hold foot on gas for a minute of fast idle.
  • How to start a cold quadrajet, press pedal fully to floor, release and then start.


Followup:
-That 1" spacer is nice. It seems to run more smoothly when warmed up. I think once the carb was up to 200 deg it did not drive as well. it was not noticeable but now with a comparison, it feels more crisp and I think it is the colder carburetor.

- I turned the idle screws a 1/4 turn richer. I have not noticed any difference, so no harm.

- after sitting for a few days the fuel is gone - but it is not as bad, I get maybe one more day of sitting

- I think the gas mileage went up, a lot. The gas pump shutoff early so I had to eyeball how much fuel that last 1/8 of a tank really represents. 24 gal tank, 1/8 = 3 gal, but we all know chevy fuel gauges 'hide' a gallon or two on the top. What size tank is it anyways? CK5 spec says 20 gal for '74 but based on when the gas pump shuts off, the most I've put in was 22.25 gal and I still had fuel in the tank. Before I post anything here, let me get another tank of gas through and see.

Next:
- The fuel pressure is still up in the air. My concern is that while cruising the fuel pump over powers the fuel needle and floods the fuel bowl, causing the air/fuel ratio to richen. I have no evidence of this and without an A/F meter I cannot check it. I have a box of parts I ordered and next chance, I will add a fuel pressure gauge.

- The carb startup is OK, but I think it can be better. I need to adjust the choke one dot more closed and see if that helps. I't be nice to understand why the one pump when warm causes a hard start. Without that pump I cant set the fast idle. Is it the fuel shot, the cracked throttle plate, or the choke plate set that causes the warm hard start?

- I have a 1" phenolic insulator I am swapping the 1" wood block with. This will cool the carb down further. The 1" wood block is the equivalent of a 1/8" phenolic insulator. So, if the carb is picking any heat from the engine now, the phenolic insulator should reduce it fully to ambient air temperature under the hood less expansion cooling, and some heat pickup from fuel. Might get the carb base down to 70 deg F. In the Q-Jet technical report from the '60s they said the hight of the q-jet is a design compromise to allow lower hoodlines on cars. That to me is engr hint for "this carb wants more height." The 1" spacer seems to work better and it might be it corrects some design geometry.

- haven't given much thought to the ignition timing, still on the list.

- I might give back a 1/16 turn of the secondary air valve that I tightened up a 1/8 turn (just tryin it out at this point, works fine as it is - no hesitation at all). If that air valve is sensitive between a 1/8 turn, what in 1/32 turns, there should be some documentation and it needs some kind of dial on that adjustment screw for reference. I can see why they added the dashpot time delay as a fix to fine tuning the air valve spring tension.

It will be a week or two until my next maintenance trip to my in-laws house. Until then I wont be posting much. One thing that stands out, and this is real, I enjoy driving the blazer more. For longer trips I was taking a zip car, it was the same price as filling my gas tank. But, my last trip I thought, the blazer is driving nice, I'll just take it. Cruising my K5 is more fun than cruising a prius any day. Then I got stuck in stop and go traffic for 4 hours with an SM 465 and mechanical clutch linkage - but it was ok, a nice stress test for cooling, 180 deg pegged the whole time. First gear and let it idle.
 
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Your mind will blow up when you stick a wideband on this.. The amount of data to be had is overwhelming. For me it was so much it validated a lot of stuff I read and invalidates a lot more. Perceptions are confirmed and proven wrong as well. It's an awesome tool for validating your senses when tuning.. No one uses these anymore. The sight smell taste and touch. Also you will see how small changes make all the differences and how some big ones don't at all.. Good luck sounds like your getting closer.
 
I've been looking online for a wideband with a datalogger that I can pull a text file from through USB. Most of them require looking at the gauge while driving and taking notes. Is there a thread on CK5 documenting tuning a quadrajet by wideband?

EDIT: Found a thread at Cliffs High Performance, go figure. This guy talks about low speed bucking. I get the same thing. I'd passed it off as using 3rd to turn a corner at 700rpm and the mix of 3.08 gears and 33" tires, plus the locker acting up. There are some turns that don't require a stop but I need to slow down - it is too fast for 2nd gear and too slow for 3rd. I have to either get down to 15 mph and down shift to ~2,000rpm, or take the chance it will start bucking in 3rd at ~600rpm.

Nice thread at Cliffs that relates some of the issues I have found (headers + fuel lines = hot fuel), suspect to find (high fuel pressure), and had no idea to look for (dripping idle needles and a few others) --> 'tip-in' test, if I pull a vacuum hose and rpm increases then I am rich, that is what I have. But, my idle screws are almost seated. So I need to add my 'dummy' air hose back in for bypass air, or open up the air bleeds.
 
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Moates.net MIGHT be able to help you out with a wideband setup, and maybe point you in the direction to get all of what you are looking for.

I've heard the innovate stuff might not be that good, but then again, the source who said that wasn't very good either. :)
 
sent them an email - I don't see a USB style data logger listed but they seem like they will understand and either have it unlisted, or know were to get one, or can cobble something together.
 
moates.net is right on the mark - they wrote back and were real honest about things and gave some suggestions of what should fit my needs.

this LM2 looks like it
http://www.innovatemotorsports.com/products/lm2.php

I need to give it some thought before setting down ~$500, gas mileage + fun factor + tuning + reuse needs to equal $500 or my wife is going to say something about buying a whole carb for that or two tires. That wideband costs 167 gallons of gas. Six or seven tanks of gas. That is 2500 miles. I go through a tank a month, so, that is the equivalent of half a years gas. If it gives me 2 miles per gallon, the pay back is, well it gives me a headache just thinking about it and I don't want to get excel out, but it is a long time, so the fun factor (not sure if the wife is going to think a wideband tuner is fun so that doubles the fun it must give - if my son was older I could factor that in but he's five) needs to be real high.
 
I've not ventured into the wideband realm myself, but you would certainly get some interesting info out of it.

I'm with you, the cost is pretty exorbitant. It's almost like an educational tool more than functionally worthwhile or necessary in your case.
 
This is really simple and cheap guys. The AEM eugo is 170 bucks and supports a serial connection, you get the cheaper wideband controlled (same sensor) plug it into a cheap laptop and log the data.
KISS principle don't make it more complex. I will tell you that you will not be able to replicate the data you will get. There will be no assumptions at all because the sensor will tell you exactly the ratio at that moment. Logging it also only helps if you can make it with relevant data like rpm and tps or map so you know load. You could rig up a map sensor and pull rpm into an input which the innovate supports and log that info.
All this talk about bypassing and adding air makes no sense when your almost as lean as can get already. Your bucking issue is a lean spot clear and simple. You come off the throttle and have zero fuel and your qjet has a weak pumpshot so you compound this with a low rpm load no fuel etc and wonder why it's bucking? Your in the wrong gear! Lol mine will do the same thing if my kickdown isn't hooked up. Dude it really sounds like tbi might be the best of all worlds for you. Simple. tuneable. Bolt on and starts whenever and wherever you want. You have a 30 year old carb you should expect less and be happier and enjoy your truck. Trust me some compromise on one place opens up fun in others.
 
I disagree Yeager if you have not used a wideband for tuning you won't realize how valuable the tool is. Basically if you know how to tune the circuits it can take you from ok carb guy to guru the first day it's on your truck.. It will save you tons of ri
 
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