Author Topic: Quadrajet choices  (Read 352 times)

Offline hiy_po

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Quadrajet choices
« on: October 01, 2019, 11:13:08 PM »
Ok second post, maybe I will get more interest in this one.
I am using a 17059596 carb on my car. Its incomplete and needs some IDCR but Its what I have intentions of sticking with.
Not so long ago I paid out for a Jet 35004 to try out.
Its a 17081206  1761 DDJ
I modified it to suit my purpose but didnt really mess around with the setup as wanted to see how it went with original settings Jet 35004 orig not factory)
https://www.facebook.com/hiypo/videos/10206714854975085/
It seemed to Idle ok but when driven on road every time I tried to get into it the engine would go off the scale rich and flood out.
I pulled it down to check it out and was a little disappointing at how rough some of the carb work was, eg throttle plate was cracked secondary air bleed tubes uneven and end of one flared. I will put up some pics of the carb.

Offline hiy_po

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Re: Quadrajet choices
« Reply #1 on: October 02, 2019, 04:02:22 AM »
Secondary Air bleeds uneven

Offline hiy_po

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Re: Quadrajet choices
« Reply #2 on: October 02, 2019, 04:03:53 AM »
Bottom of the secondary tubes

Offline hiy_po

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Re: Quadrajet choices
« Reply #3 on: October 02, 2019, 04:15:08 AM »
 Its still basically as supplied, but stripped of all its parts. It would have been on the running engine less than an hour. The secondary holes where the needles go in look huge compared to my other quaddies.
So my question is would this carb be a better choice than the one I am using.??
Can the secondaries be tamed down a bit to suit my application??
Or is it best left in its box on the shelf where it is now and continue with the 17059596 ??
The real noticeable difference I see is the main air bleeds and how they come out over the booster ventury. Is this a better design??

Offline Cliff Ruggles

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Re: Quadrajet choices
« Reply #4 on: October 02, 2019, 05:19:40 AM »
Not really much difference between a Jet carb and any other commercially "remanufactured" unit. 

Generic in every respect and if you start looking close you'll find multiple issues with them and crappy parts used to build them.

The secondary disks looked pretty large from what I can see in the pics, which is never a good thing......Cliff

Offline hiy_po

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Re: Quadrajet choices
« Reply #5 on: October 02, 2019, 06:20:52 AM »
Thank you for reply.
Mite put it on Ebay. If no one wants it be a good door stop.

Online davel

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Re: Quadrajet choices
« Reply #6 on: November 08, 2019, 09:33:51 PM »
Not really much difference between a Jet carb and any other commercially "remanufactured" unit. 

Generic in every respect and if you start looking close you'll find multiple issues with them and crappy parts used to build them.

The secondary disks looked pretty large from what I can see in the pics, which is never a good thing......Cliff

Agreed! I've acquired a couple of these Jet carbs and they have all had multiple issues. They tout themselves as "the highest quality".  They are not. Maybe they were good at some point but they certainly aren't anymore. I've also called their tech department and the "quality" there is on par with the quality of their rebuilds.

That said, I ended up with a Jet rebuild with the same problem you have (hopelessly rich secondary circuit) and the culprit was a enlarged (mangled) secondary disc as Cliff pointed out. Actually, on mine, it was just one of the discs that was damaged. But the diameter of the opening in those discs needs to be exact for the secondary circuit to transition properly. I replaced the damaged secondary disc with a new one and problem solved.

FWIW I've been able to salvage the sh1tty Jet rebuilds that I've acquired but it's always required complete teardown and retuning. I haven't had to deal with a cracked baseplate though...

Online davel

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Re: Quadrajet choices
« Reply #7 on: November 13, 2019, 07:30:38 PM »
Here's what the secondary discs looked like when I opened that Jet carb up.

Offline 77cruiser

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Re: Quadrajet choices
« Reply #8 on: November 14, 2019, 04:17:57 AM »
Did you measure them?
Jim

Offline hiy_po

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Re: Quadrajet choices
« Reply #9 on: November 14, 2019, 05:03:43 AM »

Online davel

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Re: Quadrajet choices
« Reply #10 on: November 14, 2019, 06:46:44 AM »
The disk on the right - the undamaged one - measured 0.136 which is the stock size. I replaced the damaged disk with the same size and then the carb performed fine with smooth transition to the secondary circuit. I'm pretty sure that, for street performance use, you need to have the stock size discs installed. Otherwise the carb will go way too rich during the transition when the secondary throttle blades are open and the air flaps are still closed. The fattest part of the secondary metering rods should only be a couple thousands of an inch smaller than the opening in the disk. This way fuel flow is almost fully restricted through the disks while the air flaps are closed.  I'm sure Cliff can elaborate more on this.


Online davel

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Re: Quadrajet choices
« Reply #11 on: November 14, 2019, 01:49:35 PM »
Now you're getting too much interest in your post :)

Don't mean to hi jack the thread, but another thing to consider is that you likely have a thick style airhorn gasket on that carb.  The thick gaskets can be 0.020" - 0.030" thicker than the OEM gasket.  That's great for sealing the airhorn. BUT...It also positions the secondary needles that much higher in the secondary disks.  This may require running a leaner hanger - Meaning a hanger with a higher letter.  If you have an M hanger now, you might need to run a "S" or "T" hanger.  The first post I made to this forum addressed exactly that issue with the first Jet carb I purchased - which was the only Jet carb I bought new.  Here's the post:

https://cliffshighperformance.com/simplemachinesforum/index.php/topic,3294.msg14372.html#msg14372

Your secondary discs need to be replaced with the 0.136 stock size discs first.  But if you still have loading up when the carb transitions to the secondary circuit, I would try a leaner hanger.  Or take an old hanger and file the letter off of it and bend it to see if it makes a difference.

Also, don't get discouraged.  I'm still running my original Jet carb on this truck and I've got it dialed in perfectly now.  It's my daily driver farm truck and has been running great for the past 2 years.  Took it to the track this summer and put down a 14.7 at 96mph in the 1/4.  Not bad for a 4500lb K5 Blazer with a mild 383 and SM465 manual tranny. Went through the traps redlined in second gear :)   

Offline hiy_po

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Re: Quadrajet choices
« Reply #12 on: November 14, 2019, 07:58:35 PM »
Hi Jack away. when it comes to info more is better and only crickets arent wanted.
Funny fact when I started this thread I was asking about what was the better casting of the two types I have, but it seems everyone is onto that it came from Jet and all the associated problems. So I guess it is now pretty much a doorstop.
 I have had so much success getting my carb to work with my engine, since I just started making everything smaller I am wondering what the smallest secondary disc fitted OEM is and how hard are they to change?
 I have just purchased a  7045281  2674. It appears to have the 0.135.




Online davel

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Re: Quadrajet choices
« Reply #13 on: November 15, 2019, 04:53:52 AM »
The carbs that start with 1705 and 1708 are generally better to work with since they have an Adjustable Part Throttle (APT) system.

I believe ALL quadrajets come stock with 0.136 secondary discs. They are easy to change out. They're just held in by those bronze bushings which are pressed into the casting.


Offline hiy_po

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Re: Quadrajet choices
« Reply #14 on: November 15, 2019, 06:47:33 PM »
Yes am having thoughts APT may be just adding a level of complex that I am not able to use as intended. I generally sit on about 2Hg Vac at cruise. Between 2Hg and 2psi is normal for me. Even with the softest of springs under the Power piston I still cruise at pretty much full rich.  Being able to block and delete APT/power piston saves a boost referencing modification to the carb as well.
 If I can find the combination of main air bleed area and primary main jet that is just big enough to supply my needs at cruise then have the secondaries for on boost enrichment,  I think I have brought down my Idle system to a minimal and is lean of stoich.
Main Air-Bleed Airhorn 0.064" #52                 
Main Air-Bleed body 0.040"
Primary Jet 0.072
Primary Rod 0.048
works well for me but want to find the bottom so I can sit just above it.
Main Air-Bleed Airhorn 0.064" #52  reduce to 0.040" and a 70 primary jet will be next test.
Once happy with this 1705  will transfer settings to the 704 and start the delete process

If I find some standard sec discs for the 1708 will jump on them and see if I can bring that back as well.