Author Topic: Which choke? 7044240 Buick qjet  (Read 308 times)

Offline Trans Am

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Which choke? 7044240 Buick qjet
« on: May 19, 2021, 08:29:10 PM »
Why not run mechanical choke?


I have a new to me 1972 GMC 1 ton with a chevy big block 402ci. Originally came with a Qjet(obviously), it has an edelbrock on it now and I want that gone.

I got lucky at a local boneyard and found a 7044240 on a 1972 Buick Riviera today, so that's what's going on the truck.

Truck was originally divorced choke. So was new carb. However that doesn't mean the choke parts are the same and will match up--I still got all the choke parts out of the boneyard anyways.


To start here: What exactly is wrong with the factory divorced choke?

Would it be better to use an electric divorced choke kit? There seems to be a few available.

Thank you very much.







Online Kenth

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Re: Which choke? 7044240 Buick qjet
« Reply #1 on: May 20, 2021, 01:27:30 AM »
The Tomco sticker is the main issue with your carb.
It qualifies the carb to a "frankencarb" put together with non-matching parts from X amount of different Q-jets.
Be prepaired to throw lots of money and time on it to have a proper functional carb from this.

You would be far ahead getting an old used, non-factory "restored", correct Chevy Q-jet with a Chevy divorced choke for your engine.

JMHO

Offline Cliff Ruggles

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Re: Which choke? 7044240 Buick qjet
« Reply #2 on: May 20, 2021, 01:57:14 AM »
An early Chevy divorced choke carb would certainly be a better fit, side inlet, linkage, place to hook up a return spring, etc.

Those early Buick divorced chokes are rare so make sure to save it.  You might want to wonder over to the Buick board and offer it for sale if you end up not using it.

Flags go up with the carb just from the pics, starting with the "goofy" front vent tube that started life as a PCV or vent fitting.  You still may want to take the "reman" apart and look around.  Most likely it is "hacked" which is common from the company that built is as Kenth mentioned........Cliff

Offline Trans Am

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Re: Which choke? 7044240 Buick qjet
« Reply #3 on: May 20, 2021, 04:14:41 PM »
Hey Cliff I bought your book several years ago and skimmed through it a couple times, but I've never actually been through a qjet.

I have a funny feeling I may have taken you out of context(or incorrectly altogether) when you suggested in the book that if rebuilt to factory settings and tolerances, basically any qjet could run any engine very well.

That is why I grabbed this when I could; I figured it couldn't be too hard to run. I'm not needing high performance, just a good running truck that can haul occasionally.



I understand the choke situation might be wonky, but if I'm not looking for "correct", but rather "reliable", is this carb still really not gonna work?

Why did Kenth suggest I'd be spending lots of money? Does he mean that Tomco ruined the casting? Or that the carb is just so "wrong" for my chevy that it'll never really work? The inlet position doesn't bother me and a wonky but FUNCTIONING choke doesn't disturb me either.

Offline Cliff Ruggles

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Re: Which choke? 7044240 Buick qjet
« Reply #4 on: May 21, 2021, 04:29:44 AM »
You can take nearly any Q-jet and put any calibration in it so it will work where it ends up.  So you didn't take me "out of context".

Even with that said when selecting a carb it's bet to look at all the parameters and choose one that fits your needs with less "cobbling" to get it in place.

You chose a front fuel inlet, not really a big deal there but you get a LOT more clearance toward the thermostat housing with a side inlet model.  The linkage on the big Buick carb is "goofy", and no provision to hook up a return spring rear of the carb.

The choke just doesn't work at all with a Chevy intake without some help or replacing it with a Chevy version.

Tomco like all the other companies that "remanufactured" Q-jets had a bad habit of mixing/matching components, "gutting" the original calibrations out of them, then installing "generic" calibrations and cheap parts.  You will also find that many of them received the POS pressed-in N/S assemblies which are HOPELESS and leave the carb nothing put a pile of junk.

At a minimum decide if you can work with the linkage and choke parts before throwing a lot of time/funds at it.

There are literally millions of good cores still out there and easy to obtain at relatively low prices.

I use and prefer the 1976 and later non-CCC side inlet carbs (hot air or electric choke) for what you are doing.  They Chevy versions will be side inlet, PLENTY of places to hook up linkage, return springs, convert easily to E-choke, and fully adjustable via the APT system without having to remove the airhorn and change parts.

IF you are wanting to use th early stock intake then go after a 1969 or newer Chevy divorced choke carb instead, preferably 1972-1977.  They are EXCELLENT units as well, and have the correct choke set-up already on them.

I actually have scores of them here in the core pile.  My personal favorites in the bunch are the 1977-78 truck units with the SMAB set-up.  They are at the top of the pile for Chevy divorced choke models but even with that said the four MAB style will work just fine if that's what you end up with........Cliff

Offline Trans Am

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Re: Which choke? 7044240 Buick qjet
« Reply #5 on: May 21, 2021, 04:24:19 PM »
So I guess my initial question was never answered: can I get an "electric divorced choke conversion kit" and make it work?


If there is a pressed in N/S, does that mean you can't replace it with a proper screw in type?

Offline Trans Am

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Re: Which choke? 7044240 Buick qjet
« Reply #6 on: May 21, 2021, 07:19:53 PM »
So here is a list of other Qjets I have laying around. Can you tell just by the numbers which one might be my best selection? Or do you need pictures of each unit?
Are the two 1975 units the dreaded ones that are useless?


7045505

17059553

7045224

17056228(tinkered with and "remanufactured"

17059530

17058512

Online Kenth

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Re: Which choke? 7044240 Buick qjet
« Reply #7 on: May 22, 2021, 03:15:49 AM »
17058512 Chevy style, needs .050" main airbleed inserts or different jetting.
17059553 Olds style.
17059530 Cadillac style, no hook-up for TV cable.

These are fine 800 cfm castings.




Offline Cliff Ruggles

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Re: Which choke? 7044240 Buick qjet
« Reply #8 on: May 22, 2021, 04:39:38 AM »
With enough "cobbling" you could probably make an aftermarket electric divorced choke work. 

They are marketing electric choke conversions for the divorced choke carbs.  Have had a few sent in here with them in place and NOT a fan.

If you run into a "pressed in" N/S assembly the carb is JUNK.  That modifications removes the threads for the OEM style seat.

The best carb in your bunch with minimal work is the 17059553. 

Use a short filter housing on it and one of my Marine filters.  Convert to E-choke.  I can provide a rebuild kit with tuning parts so it's dialed in exactly for what you are doing right off the bench.

The big Caddy carb is second, and you can replace the throttle shaft with one from a later model Chevy carb.  It a little closer than the large MAB models without as much work, but no better anyplace otherwise.

I spend at least 8-10 hours every day putting together custom rebuild kits with tuning parts for these carburetors.  I just need ALL the engine/drivetrain/vehicle specs and a carburetor part number.  At this point I know all the numbers, what they came with, and what they need to use in any particular application.........Cliff

Offline Trans Am

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Re: Which choke? 7044240 Buick qjet
« Reply #9 on: May 22, 2021, 06:30:13 AM »
Can I also ask, are the two 1975 units absolute crap without a doubt or do they need to be torn down to see if they have that balance port?

Kenth, thank you for your clarification, that helps me in the future with those carbs no matter where they go.

Thank you cliff, I'll get the 9553 and take some pics to let you see up close if it seems ok.
Later today or tomorrow I'll reply with as much info as I can, but I'd like to say now with all openness: I just got this truck a month ago. I was told the engine was rebuilt but I have NO idea if it was a stock rebuild or what. I don't know the bore size if it was changed. I don't know the cam if it was changed. I don't even have the rear gear exactly but could verify roughly using a speed test. The diff cover doesn't leak and i don't want to remove it to inspect the teeth for ratio. Factory manual says it can "only" be a 4.10 but who knows.

This is a work truck and the old 402 big block will probably never see over 3500 rpm for the rest of it's life.

« Last Edit: May 22, 2021, 06:41:55 AM by Trans Am »

Offline Glutenfreecarbs

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Re: Which choke? 7044240 Buick qjet
« Reply #10 on: May 22, 2021, 10:49:23 AM »
Trans Am, I'm selling a freshly-rebuilt 17083226 that might be a great fit for your truck. Chevy-style throttle/trans linkage, side fuel inlet, electric choke, etc. It's not pretty or re-plated, but it's got Cliff's SR Rebuild kit and runs great; I actually drove it to work Monday through Wednesday of last week.

http://ebay.us/NvvgsP?cmpnId=5338273189



Offline Trans Am

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Re: Which choke? 7044240 Buick qjet
« Reply #11 on: May 22, 2021, 04:02:30 PM »
Trans Am, I'm selling a freshly-rebuilt 17083226 that might be a great fit for your truck. Chevy-style throttle/trans linkage, side fuel inlet, electric choke, etc. It's not pretty or re-plated, but it's got Cliff's SR Rebuild kit and runs great; I actually drove it to work Monday through Wednesday of last week.

http://ebay.us/NvvgsP?cmpnId=5338273189
No thanks man, looking for more DIY.

Offline Cliff Ruggles

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Re: Which choke? 7044240 Buick qjet
« Reply #12 on: May 23, 2021, 04:35:32 AM »
"I was told the engine was rebuilt but I have NO idea if it was a stock rebuild or what. I don't know the bore size if it was changed. I don't know the cam if it was changed."

Not really a big deal, if it isn't hammering really loud and the County is trying to hire you to kill mosquitoes this summer from the burned oil smoke it's probably OK!

At a minimum I would do a vacuum test at idle speed and a compression test in all cylinders. 

The vacuum will give you a relative idea as to how much camshaft was installed during the "rebuild".  A cranking compression test will also let you know if the cam was well chosen for the compression ratio and at the same time how well the rings are sealing up.

Knowing the vacuum produced at idle, idle quality and cranking pressure also helps me when choosing tuning parts and how to set up the carbs idle system so it will work perfectly once placed in service.

Big Block Chevy engines sadly were really "low" compression in those years.  They also had crappy cams in them and late cam timing.  All that was done to please the EPA, not the end user.  They are however excellent otherwise, just sitting their waiting to be exploited.

I've helped quite a few later model 454 "truck" engines by improving the "squeeze" in them a tad, tighter squish, well chosen cam and they literally pick up 100hp and an least that much torque!  No need to spend a lot of money on them either, the "truck" heads are more than adequate for the task.  They just need higher compression and improved cam timing.  Even the "flat" iron intakes are excellent even though folks have labeled them "door stops" and been tossing them in scrap piles for decades.

Recently had a customer do a "stock appearing" 1970 Chevelle SS.  I supplied the carb for his 454 (bored and stroked to 496).  The engine "builder" targeted 560-580hp and under his breath told the owner that the POS stock iron intake and Q-jet would NEVER "feed his engine". 

I get a call on dyno day and it isn't making chit for power, around 425hp and DONE at 4500rpm's.  I tried to help the engine builder/dyno operator with some questions and such but he was so focused on bad-mouthing the intake and carb it was difficult.  Finally I got around to asking about the timing and distributor.  He told me he installed a Pertronix and timed the engine right at 36 degrees total for dyno pulls.  I told him to remove the Pertronix and put points back in it as I've seen GOBS of those modules not work well in recent years.

Reluctantly he put the points back in it and went back to dyno testing.  I get a call about an hour later from the owner that it made 565hp/587tq on the very next pull!  So don't think for a minute the stock intakes and carbs are not adequate for you average 396-454 engine build....FWIW.....Cliff
« Last Edit: May 23, 2021, 08:38:54 AM by Cliff Ruggles »

Offline Trans Am

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Re: Which choke? 7044240 Buick qjet
« Reply #13 on: May 23, 2021, 06:08:26 AM »
OK I'll try and complete those tests in the next two days, simple enough

Offline Trans Am

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Re: Which choke? 7044240 Buick qjet
« Reply #14 on: May 25, 2021, 09:04:58 PM »
Compression was an even 140-145 for all cylinders. Vacuum gauge appeared to stick so I'll get another one but If I tapped the gauge it would react. Vacuum read was ~15 at 600rpm, it wouldn't get to 18 nless it revved to about 900 or so.
It seems to idle rough, timing was set at 12ยบ BTDC.


I can't imagine the farmer who owned it would have asked for a mild cam--of all things-- to be installed, just sounds very silly. But who knows....vacuum gauge is definitely not in good condition but honestly the thing idles way rough for what I'd think is correct for stock.....but again, the thought of a farmer installing a lopey idle cam is just silly....
I'd also like to clarify that I was told the engine was rebuild long ago, but everything is clean around the engine. At speed it runs very smooth, just idle is lopey. Get it to 1000rpm and it sounds perfectly smooth and stock.
« Last Edit: May 25, 2021, 09:08:21 PM by Trans Am »