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Quadrajet Carb Talk and Tips / Re: Q-jet with 3 mixture screws? 17085213
« Last post by Cliff Ruggles on May 09, 2021, 05:32:06 AM »
Those are HD truck/motorhome carburetors and used special castings with an adjustable secondary airbleed/enrichment system.   Most likely due to the fact that those engines would spend a lot of time on the secondaries towing and climbing hills and steep grades.

Most showed up on HD 454 truck engines but I've seen a few used on 350 HD engines as well.

The special full tapered 61 primary rods are correct but I've never seen 78 jets in one to date.  I suspect those were added by a well meaning tuner that didn't under stand the APT system, which on that model is a little different than others being adjustable for height and travel/limit of the PP.

They have a pretty rich idle set-up for an emission years carb.  Most are part numbers 17085212 and 17085213, but they were made with a couple other part numbers as well.  17085000, 17085003 comes to mind or something close to that.

Be warned that they use different parts and gaskets and will NOT work well if the wrong ones are installed during the rebuild.......Cliff
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Quadrajet Carb Talk and Tips / Re: Cadillac Q-jet 7040230 - with photos!
« Last post by Cliff Ruggles on May 09, 2021, 03:34:41 AM »
Zero failures with the late style closed cell nitrophyl floats to date. 

Brass floats are not the correct weight or buoyancy and I've seen scores of them fail over the years, especially this newer production stuff.  I suspect the ethanol in the fuel may eat the solder out of the seams, or they are just junk right to start with.......
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Quadrajet Carb Talk and Tips / Re: Q-jet with 3 mixture screws? 17085213
« Last post by tayto on May 08, 2021, 07:28:21 PM »
It's for a hot idle compensator. I rebuilt a Qjet for a '80 Firebird and it had one. I believe Cliff recommended to block it.
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Quadrajet Carb Talk and Tips / Q-jet with 3 mixture screws? 17085213
« Last post by Glutenfreecarbs on May 08, 2021, 11:29:27 AM »
This is my current daily driver, P/N 17085213. It has a hidden and capped adjustment screw, which somehow connects to both the throttle body and the secondary fuel wells. I have no idea what any of it does, but it's been a great summer carburetor, mainly because it has an A/C idle solenoid to keep the RPMs up when my giant axial R-12 compressor kicks on during a traffic jam.

This carburetor also came with big cone-shaped "61S" primary metering rods and .078" jets. It's hard to imagine a heavy truck/van/RV would be happy cruising with such a lean mixture, but I guess that's what The General prescribed...



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Quadrajet Carb Talk and Tips / Re: Cadillac Q-jet 7040230 - with photos!
« Last post by Glutenfreecarbs on May 08, 2021, 10:57:57 AM »
Thanks for the pointers! I've always used brass floats because I just don't know which suppliers or materials of plastic floats to trust. However, I installed one of Cliff's floats from his "SR Rebuild Kit" last night, and I was impressed by how light and rigid it felt. Maybe it's time to change my ways...
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Quadrajet Carb Talk and Tips / Re: Cadillac Q-jet 7040230 - with photos!
« Last post by Cliff Ruggles on May 08, 2021, 05:52:03 AM »
Good tip on installing the clip thru the holes in the float arm.

Another good tip is to NEVER use a brass float in a Quadrajet, especially the early design with poorly located short hinge pin.

That design was NOT good from day one and doesn't provide enough leverage on the N/S assembly for good fuel control.  Makes things even worse to come along and put a heavy and much smaller brass float in place.

I've replaced hundreds of brass floats in those carbs sent here from customers having fuel control issues.  The even make another type of brass float with the arms soldered on top that are even more hopeless!

We've also ran into issues with current production brass floats leaking at the soldered joints so avoid them in other models of carbs as well, like 2 JET, AFB's, etc........
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I always use Rhoads on flat tappet camshafts as there are no negatives anyplace.

With the right cam you cam mimic the power of a very well chose Hydraulic Roller cam at much less cost.

I did a back to back dyno test on my last 455 engine between a 304/314, 231/240, 113LSA cam and a Comp HR cam with 284/296, 230/242, 112 specs.  The roller cam had .361" lobes and a LOT more lift than the flat cam. 

The roller cam only made 3hp/4ft lbs more power than the flat cam and done at 5400rpms where the flat cam made peak power at 5600rpms.

At the track the roller cam was worth more than the dyno showed, running about a tenth or so quicker for most runs and a solid 2mph faster.

Best run ever with the flat cam was 11.64 @ 116mph.  The roller cam went 11.52 @ 118mph.

What the Rhoads lifter do is allow us to use a relatively large cam with less negatives, and have a variable valve timing set-up in an older engine design. 

I've back to back tested them on the dyno against HT-951-R lifters and there is no power loss whatsoever from the fast bleed design.......Cliff
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Quadrajet Carb Talk and Tips / Re: Suggestions For Next Drag Strip Testing Day
« Last post by tayto on May 07, 2021, 02:33:40 PM »
Cliff do you still use and recommend Rhoads lifters? I've heard good things, and was thinking about trying them in my  roller SBC one day.
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Quadrajet Carb Talk and Tips / Re: Cadillac Q-jet 7040230 - with photos!
« Last post by Kenth on May 07, 2021, 01:15:57 PM »
Look here:
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Quadrajet Carb Talk and Tips / Cadillac Q-jet 7040230 - with photos!
« Last post by Glutenfreecarbs on May 07, 2021, 11:20:14 AM »
Just wanted to show off my winter carburetor: a 1970 Cadillac unit, modified with electric choke, Chevy throttle linkage, and a special adapter for 3/8" fuel line. It's been a great daily driver, and very simple to work on!

(Mods: please delete my previous thread, I broke the embedded images while playing with sizing...)







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