Re: Q jet power piston spring
 

Surprised..10 posts before anyone mentioned this.
I didn't think anyone used the primary enrichment circuit anymore ;-)

Re: Q jet power piston spring
 

I’ve never built any for stock or super stock but several for dirt cars and I never use primary rods.
Terry

Re: Q jet power piston spring
 

I've never found the need to eliminate the power enrichment circuit in a Rochester QuadraJet. Properly tuned, it will run cleaner and work better with the circuit operational. It really doesn't need to be made stupid like a Holley.


The power piston springs are usually color coded, the soft one to use in MOST low idle vacuum race applications is orange.


The power piston spring isn't a huge factor in an all out drag race application, UNLESS you are leaving the starting line from a dead idle.



I haven't run into any engines that will idle and not maintain enough vacuum to hold a power piston on an orange spring down.


The first question is, do you "think" the engine is running rich, or do you KNOW?


If the throttle blades are closed enough to be on the idle circuit, the power enrichment circuit isn't operating.


You can check to see if it is open by using a "coffee stirrer" to push on the top of the power piston assembly. First, without the engine running, put the stick in the primary vent tube, and find the top of the power piston assembly, you'll be able to push on it, and feel it compress. With the engine running, repeat that procedure, the piston should be at the bottom of the bore and no movement should be possible.



If it is "pulling over" you'll be able to see it, and either the float level is too high, the fuel pressure is too high and is over coming the float and needle and seat assembly, or the throttle blades are too far open.


Make certain the main well plugs are not leaking, the float level is at 5/16" or lower, the fuel pressure is not too high, the needle and seat are sealing, and that the throttle blades are not open too far. As mentioned above, in some cases a simple cure for the throttle blades being open too far is a 0.090" to 0.125" hole in the primary throttle blades.


Make sure that no one has blocked off the idle air passages, as is common with "remanufactured" carburetors.



If you own a race car with a Rochester QuadraJet, and you don't own the Doug Roe book, and the Cliff Ruggles book, you're making your life extremely hard for no reason.

Re: Q jet power piston spring
 

And that's a wrap! This thread can end now as Alan has just told everyone all you need to know about this subject. Well done Sir! Merry CHRISTmas to all.

Re: Q jet power piston spring
 

Not sure but I would think that stocker a with a too light of a spring once it starts regaining vacuum on the top end would start plugging rods back down and lean it out. Lean is mean but so is the parts bill.
Terry

Re: Q jet power piston spring
 

Alan, all >

I didn't mean to imply that it was some kind of speed secret to eliminate the primary rods.
I've run the same stocker, both ways,... true foot braking it to about 2800-3000 , and never saw a bit of ET movement, either way.
So, the answer is, once again...It depends.

On a Sportsman bracket car, where two stepping is not allowed, but deep staging is, keeping it clean at about 1500 is a good idea.
As mentioned, there are many ways to go about that. A modern, multi-spark ignition goes a long way here.

Stick shift car? Different world, but I've never seen much difference here either.

Bottom line..Pick your poison , and don't stop till ya get enough :-)

Re: Q jet power piston spring
 

Danny, you are entirely too kind. I only covered a few of the foundational basics, but at least enough to get a smart racer willing to work the basics needed to get a grasp on things, and a direction to go.


And a VERY Merry Christmas to you as well sir.

Re: Q jet power piston spring
 

Oh, by all means, my way is not necessarily the only way, or even the best way. It's what I learned, from 40 years of working on QuadraJets, and from guys like Ashley, Oliver, Bridges, and Schindler.


The QuadraJet is very sophisticated. I suppose for many, eliminating the power enrichment circuit simplifies things. I prefer to use everything it offers.


Your mileage may vary.

Re: Q jet power piston spring
 

Well, few QuadraJet combinations are capable of moving so much air that a 750 or 800 cfm carburetor will become such a restriction that they generate more than 5"- 8" of vacuum, you MIGHT see that on one of the 454 Super Stock engines. If memory serves correct, the orange power piston spring, for example, will overcome 10" to 12" of vacuum. Remember, most 4 barrel carburetors are rated for cfm at 2.5" of vacuum.