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Discussion Starter #1
My 74 started running rich, so I decided to rebuild it. The carb # is 7044233 Cadillac Commercial Chassis}, and the car was running great until this year.

I was very careful to put all of the parts in a magnetic bowl, but I think I am missing the power piston spring, or maybe not.

Here's my dilema:
The APT screw was never touched. It is the type that runs horizontal into a bent clip, and it is capped off with an aluminum plug in the throttle body near the inlet. With the carb apart, and no spring in the power piston, the piston arm is about 3/8" above the carb gasket surface. with the original metering rods in place, this puts them in a position where only the small part of the rod is in the jet. This leads me to believe that even if there was a spring, it would not change the enrichment when the vacuum drops at all.

Was the carb set up without the spring, or have gremlins gone under my hood and adjusted the APT and replaced the plug?

I have searched all over for info on Q-Jet parts listings for Cadillacs, but only found Chevy, Buick, and Pontiac.
 

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All Quadrajets have power piston springs.If you don't install one the metering rods will not raise up out of the jets when you loose vacuum.A 1974 Quadrajet doesn't have APT either.You are referring to the screw on the front of the carb that let's you raise or lower the height of the metering rods.My suggestion is not to move it.Make sure that you put the power piston spring back in there.If you didn't it's going to be real lean at anything other than slightly cracking the throttle.The metering rods will always sit high with the top of the carb off with the spring underneath the power piston.Because the top of the carb pushes them down in the jets and the spring pushes them up when you loose vacuum.Make sure that you clean it real well.
Quadrajet's don't like trash in the fuel bowl and it will cause a rough idle and and poor performance.
 

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Hates: Liver. Loves: Diesel
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I thought APT started in 76 with the new airhorn design. The older ones have that cast-in "double ramp" in the air horn where the screw would need to be.
 

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Discussion Starter #4
To clarify, I think the rods are too far high without the spring.
This pic is blurry, but there is no spring under the piston in this photo, and the hanger is 3/8" above the carb body. The rods are so far out of the jets, that the small part of the taper is the only part in the jet.
With a 66 jet, and a 36b rod, this might be right, but it just seems strange.

I'll put the strongest spring from Edelbrock in and give it a shot.



This link shows my style of power piston.
There is a pin at the bottom of the piston. It is fixed.
Early power piston
 

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Are you replacing the metering rods?Make sure that you are getting some for a 74 quadrajet.The newer quadrajet's use a shorter metering rod than the older models.It's not a big difference in length but it may be the reason why the fat part of the rod is not getting down near the top of the jet.I can't remember what year they changed the rod length but it is different.
 

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Discussion Starter #6
Finally, a pic of the plug that blocks the older APT screw, indicated by the red arrow.


The rods were exactly the same size as the originals 36B. Edelbrock part # 1936.

PS, I wrapped a small piece of tape around one of the old rods just to mark where the taoer starts, and it's better than I thought. The taper does start outside of the jet, but not by much. This measurement, as before, was fully seated without the soring, and the throttle body screws tightened appropriately.

It looks ok, so I will go ahead and finish the job.

PS, it was thoroughly cleaned, rinsed with mineral sprits in a parts washer, and blown out with compressed air.

AS a final step, the plugs were epoxied.
 
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