Author Topic: Did they mix the parts ?  (Read 312 times)

Offline Erick

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Did they mix the parts ?
« on: March 29, 2024, 08:26:59 AM »
I'm new to this forum and of course I'm having problems with my carburetor.
I recently changed my Corvette carburator from Holley to a Quadrajet.
So I'm the "lucky" owner from a uremco "remanufactured" Q-Jet.
Because I was unable to adjust that carb, I made some research and with the help from the net, Lars from corvette forum and Cliff's book, I discovered what those "remanufaturers" are able to do. On my carb were missing power piston bottom pin, air horn main air bleed, main body main air bleed and  idle air bypass was plugged.
Before going further and order a recalibration kit for my aplication, I would like to be sure that they don't mix the parts, so i hope that with the following pictures one of you will be able to tell me if airhorn and base plate are the good ones for that 1972 350CI truck carb (704 2210 ).

Online Kenth

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Re: Did they mix the parts ?
« Reply #1 on: March 29, 2024, 09:51:51 AM »
Looks like a genuine 7042210.
These units have .120" MAB´s in airhorn and float bowl, no brass inserts.
Cut power piston is a bummer, never understood why they do this.
Plugged idle bypass air is a cheap way to richen up the low speed circuit, doesn´t work well with ported source to the ignition vacuum advance.
Factory jetting is 43B primary rods, #74 main jets and DA secondary rods.

Offline Erick

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Re: Did they mix the parts ?
« Reply #2 on: March 29, 2024, 11:53:03 AM »
Thank's Kenth. Finally some good news. It seems it will possible to adjust that carb.
I machined a new pin for the power piston which I re-sleeved in place and removed the lead plugs.
So now engine idle is much better, sparkplugs are no more black and the idle mixture screw finally useful.
But there are small hesitations at cruise around 2000RPM, slight engine stumble.
Factory jetting is ok ( 43B primary rods, #74 main jets and DA secondary rods)
Idle tube and idle down have also been changed by remanufacturer, I don't know if it's orginal manufaturer size for that carb
idle tube : 0.029
idle down restriction : 0.047
So I suppose there are some modifications to do with my engine specifications.

Online Kenth

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Re: Did they mix the parts ?
« Reply #3 on: March 29, 2024, 02:40:38 PM »
As for the idle circuit i have found the 1972 Chevy Truck Qjets have .039"-.040" idle tubes, .092" upper idle air bleeds,  .051"-.052" idle down channels, .063" lower idle air bleeds, .095" idle bypass air holes in throttle plate and .086" idle needle holes.

HTH

Offline Erick

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Re: Did they mix the parts ?
« Reply #4 on: March 30, 2024, 11:30:05 AM »
So upper idle air bleeds, lower idle bleeds and idle needle holes, jets and needles are the good size
Idle bypass holes are larger .0137
idle tubes smaller  0.029
idle down chanel restriction smaller  0.047
I don't know the possible effects from those changements.
Kenth, thanks for all those informations.

Online Kenth

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Re: Did they mix the parts ?
« Reply #5 on: March 30, 2024, 01:06:57 PM »
Chevy BB Qjets of this vintage uses .137" idle bypass, so throttle plate may have been swapped.
Who knows if the carb has been thru an earlier "remanufacturer" and had the idle tubes and downchannels drilled out for a "top fuel dragster", and that the latest company tried to get it back to factory specs without knowing the proper specs?
Easy enough to drill the idle tubes with a #61 drill and the idle down channels with a 1.3 mm to have the correct sizes for this unit. The idle bypass holes in the plate can be threaded from above for 1/4" brass set screws drilled to .095".
This will restore the performance and cure any hesitation.

Offline Erick

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Re: Did they mix the parts ?
« Reply #6 on: March 31, 2024, 07:32:37 AM »
Kenth, I will follow your advice.  I have ordered all what I need. It will take a while before I receive what I need to make the changes.
By the way, how to be sure that the power piston spring is the good one?

Offline Cliff Ruggles

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Re: Did they mix the parts ?
« Reply #7 on: March 31, 2024, 08:45:38 PM »
Just curious, what did Lars tell you to do with that carburetor?....


Offline Erick

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Re: Did they mix the parts ?
« Reply #8 on: April 01, 2024, 08:17:13 AM »
"Yes, you have unfortunately ended up with a "Uremco" carb, which is a horrible pile of junk".
He sent to me an article outlining just a few of the common problems and issues with the "remanufactured" carbs and wrote the fact that they will use mismatched parts and components from various different model years and makes that are not compatible with each other.
With the pictures I sent to him, he told me that the power piston pin was missing and that they should have plugged the air idle system. And it was possible too that they made changes, IFR, restrictor... He was right.
I bought this one without knowing anything about q-jet.
I discover now those carbs...
The problem is that it's not easy to find q-jet here in France, I thought to buy a clean carb and I could buy another one with other different problems..
That's why I'm trying to learn more and it seems that with all the infos I got , it will be possible to restore it to original specifications.

After that, there will definitely be some adjustments to do because my engine is a 327CI with flat top pistons, Edelbrock Performer RPM 70cc heads and Crane Cam H-260-2 Intake @Cam 2847 @Valve 484 Exhaust @ Cam 3027 @Valve 515

Offline Mudsport96

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Re: Did they mix the parts ?
« Reply #9 on: April 01, 2024, 11:43:08 AM »
That Camshaft has specifications of the big block cam. Is that the correct part number? That cam will not fit in a 327

Offline Erick

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Re: Did they mix the parts ?
« Reply #10 on: April 02, 2024, 12:15:39 AM »
There is something strange with the camshaft code. 25 years later i still have the original bos wit the old camshaft inside. So I checked again, it's printed H-206-2 but also 113901 and with that number I find following specifications for a small block
Camshaft - Hydraulic Flat Tappet - Lift 0.427 / 0.454 in - Duration 260 / 272 - 112 LSA - 1200 / 5000 RPM - Small Block Chevy
So first time I pick-up wrong specs with tipping only H-260-2...

Online Kenth

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Re: Did they mix the parts ?
« Reply #11 on: April 02, 2024, 02:20:18 AM »
Camshaft Part-#113901 with the H-260-2 grind.

https://www.summitracing.com/parts/crn-113901


Offline Erick

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Re: Did they mix the parts ?
« Reply #12 on: April 02, 2024, 03:39:23 AM »
That's right.

Offline Cliff Ruggles

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Re: Did they mix the parts ?
« Reply #13 on: April 04, 2024, 04:57:04 AM »
My advice would be to obtain an unmolested core and ditch the remanufactured unit and chalk it up to experience.  I woln't touch any of those here, and neither will Lars, and for good reason.  The miss-matching and "butcher" job they recieve make it difficult, and sometimes near impossible to get a good end result.  Even if you do the time/funds spent far exceed simply getting a good core and complete/correct rebuild kit and put your efforts there in the first place......FWIW.....