Technical Tuning Quadrajet help needed

If you google"qjet base gasket" or " qjetparts.com" you'll see some of the options , if the manifold came off a 60's sbc , it's likely to need the 2 if not the 3 piece stack ...

 

That type of intake has a composition (metal and gray stuff) gasket with a stainless steel "shim" above it. The trough is where exhaust gas travels across when the heat riser valve is closed, to help warm the carb so fuel will atomize well when it's cold out.

Chevy used that design from about 1965-69.

And yes, they do expect the carb base to seal directly to the stainless piece, there is no gasket above the stainless.

 

Not to hi-jack the thread here, but that's a spiffy new avatar you've got there squirrel!!! [emoji41]

 

thanks! the P. L. Newman racing jacket I made, for the LeMons Rally. We're supposed to dress up/have a theme, mine was Doc Hudson/Paul Newman in the 1980s.

 

LMFAO!!! [emoji23]
You nailed it!!!

 

The manifold you have is an early design that obviously didn't work well. If it did they wouldn't have changed it. I drive 1/2 inch soft plugs into the holes that are on each side of the slot. Then I still use a plate under the carb base.

 

I've used that design intake for a long time on a few different vehicles, it works fine if you ***emble it as designed.

 

Yep !

 

I was taught to adjust the secondary's by crimping the vacuum tubing that the vacuum hose slides over, not tightening the spring. That spring is only there to close the flap.
Open the crimp on the tubing until you feel a bog when you bring on the secondary's, then start crimping a little at a time until it goes away..
My neighbor taught me this, the Pontiac dealership he worked at sent the techs to school to learn how to work on the Quadrajet.. That's were he learned this.. I've straighten out a lot of Quadrajets over the years using his method..

 

I thought that WAS Paul Newman in your avatar ! ! !

 

The spring is adjustable , the number of turns to the adjustment screw was always clearly spec'd in the carb rebuild data for the carb number you were rebuilding , like alot of things , failure to read and follow directions leads to all sort of tomfoolery !

 

The secondary air valve needs to be fairly stiff. Just poke it with your finger, if it flops open easily, the spring is too limber. Realize there is an allen lock screw holding it that you have to loosen to make the adjustment. Have the screwdriver in the slot when you loosen it, or it will completely unwind and you have no idea where you started.
You can also bend the tang stopping it from opening quite as far, if you dont need all that air flow. Most of the dinking around I did with these was on a dirt car, youd be surprised how much those two things affected how crisp the car came off the corner.
Good Luck

 

I've been building and using Q-Jets for 40 years and this is a method that I had not heard or read about, interesting concept.

 

One thing I didn't mention yet is that in addition to the adjustments, you need to make sure all the vacuum diaphragms are still working. Some have one, some have two. They are used for the choke pulloff, and for the secondary air valve.

Since the originals would be close to 50 years old, it's possible they're acting up.

 

If the engine is stock, and the carb is correct, and the carb has been properly rebuilt, then the "crimp" is totally unnecessary. The air valve should be adjusted.

No offense, I don't like the idea of the "crimp". Seems like a band-aid with old sticky glue!

Rochester DID use choke pull-offs with different internal orifices to adjust the timing of the airvalve opening; so the IDEA of the crimp has some merit. I just prefer changing to a different CPO for the adjustment. Crimping would make any kind of scientific adjustment difficult, if not impossible. As in my first paragraph, this adjustment is totally unnecessary using stock components. Only if the Q-Jet has been migrated to a vastly different engine, or the engine has been very highly modified, is this adjustment necessary.

What many enthusiasts fail to do when rebuilding a Q-Jet is to replace both the airvalve spring, and the plastic secondary cam (the one controlling the secondary rods). These parts come in the better rebuilding kits.

I have seen as much as 0.050 wear on the cam. Due to the location of the cam, the reduction in lift on the secondary rods is twice the wear on the cam.

Jon.

 

Here's a guy who knows how to properly adjust the secondary air valve on a Qjet. And I'd bet it didn't involve crimping the vacuum fitting on the pull-off. Watch close at the end of the run where he's off the throttle and you can see just the last little bit of fuel splash on the air valve from the secondary transfer slots, I believe.

 

For what it's worth, I had a nice original '68 Corvette with this same carb/gasket setup. I thought I was smart and took it off and replaced it with a single gasket. The car wouldn't run for **** when I did that, so I went back to the stock setup, which made the car run good again.

 

Hey again guys, I've been tinkering as able during the week and yesterday discovered that my alternator had died so between installing an e-choke (the block part of the divorced choke was not installed, need to have a talk with the old man about that!) I haven't got much "tuning" done.

I do however have another question. When should ignition tuning be done? after the fueling tuning is complete? I've done exactly zero distributor work in my life so that will be my next foray into google research.

I also found a really nice paper by Lars Grimsrud (http://www.capitalcorvetteclub.ca/attachments/article/92/Q-Jet Tuning Paper.pdf) that has helped a newb like me considerably.

 

Get the timing sorted out before you try to get too far with idle adjustments.

 

Generally what I found, carburetors are dependent on manifold signal especially at idle is where it's really noticeable but everwhere else too, and ignition timing and valve timing directly affects the average manifold vacuum levels. If the average manifold vacuum levels aren't right at any given operating point, the carb will not tune right. It is calibrated from the factory for a certain signal and flow.

 

I don't think there is anything wrong with the timing (probably should have opened with that). But what symptoms would I listen/feel for if the ignition needs adjustment? And on that should I inspect points or anything else in the distributer? Is there a frequency that things like that should be done in?

I took it for a drive after tweaking the idle screws a smidge rich this morning and I'm getting:
Idle 12:1
Part throttle 13-16:1
"WOT" 13-14:1

Driving it in town I don't have a lot of opprotunity to punch it so I probably never get the secondaries to even crack, but from a roll if I put my foot in it the AFR drops and holds. I may add a touch more fuel from the mixture screws, but for putzing around in I think I'm pretty comfortable with those numbers being safe for the engine.

 

I would be reasonably happy with them.

Do you have a timing light with a knob or display on it, so you can read the degrees of timing advance?

Do you have a dwell meter?

 

Nope, neither of them.

 

Then you won't get too far on your tune up. See what you can find...usually dwell meters show up at yard sales....but you should be able to buy a new timing light, I think. Although new cars haven't needed them for a decade or two or three.

 

Poor ignition timing, the advance has to be right from idle to cruise or it won't run right. And valve timing. A stretched or worn out timing chain set will reduce power quite a bit.

Get yourself an old MoToRs manual, from about 1955 or so. They had this **** figured cold out a long time ago. Compression test, vacuum test, ignition, carb tuning, in roughly that order. If I was only allowed one tune-up tool for some reason it would probably be a mechanic's vacuum gauge. It tells pretty much everything if you know how to read it.

 

I have had a vacuum gauge since the late 70s, I use it maybe once every five to ten years. Maybe I'm missing out?

 

If you had to repair other people's **** all the time, yes. You already know all this stuff. On the automotive forums, somebody shows up "My '62 Schmedlap is popping and backfiring. What could it be?"

They want "the answer", a simple tweak of a carb screw or something and Everything Will Be All Better Now. LOL. Everybody wants a smooth running mo'chine, but they don't want to do the work to get it that way. They don't want to check compression, vacuum test, timing light, tach, even a ****ing voltmeter is a Bridge Too Far.

 

that buick qjet is an 800 cfm unit and used on the 455's and 350's. maybe its too big for your chevy.
on the v8buick website there are a couple of guys that do them. one in ct and one in tx.

 

Oh yeah, it's way oversized. I wonder if I'll ever get the secondaries to open.

But I have it sorted out sufficiently to drive it comfortably. It's a heavy truck with a little V8 after

 

The glory of the quadrajet is the variable venture on the secondary. You've got small primaries and the secondaries only p*** the amount of air the engine is asking for. If it's a smaller motor the air valve on the secondary just won't open as far, unless somebody ****ed around with the spring on it.