jensenracing77

I am wondering about the power piston spring in a Quadrajet carburetor. Looks like I will not be over a 14 inch vacuum and my carburetor guy is telling me there is no spring for the power piston to go this low on the vacuum. He said he will have to take the power piston out altogether like the 4 speed carburetors were. I didn't think 14 was all that low. do any of you have experience with this or have any suggestions? If I don't have the power piston and go strictly by jetting, how does this affect performance, driveability, and economy?

Koda

You can clip coils down to 11", I've heard, and it was the w-30s I think that had two barrel jets and no metering rods/pistons, not just any 4 speed.

BILL DEMMER

7037734 spring has a cut-in point at 14" hg, 7032758 is 11" hg, 7037305 is 10" hg, 7036019 is 8" hg.

it was the '70 w30 m/t (only) that had no power piston, power piston spring, or primary rods, and used 2g jets.


bill

455man

You can order the different springs online.

jensenracing77

Back to this subject. Sparky's carburetor is still telling me that 14 is to low to run the power piston. My dyno guy said it will be ok and also several others tell me it is ok. I am not sure what to do? Any recommendations?

455man

Try this.

http://quadrajetparts.com/rochester-...548097ce813da9

Spring / Inches of Vac. / Length
Yellow: / (2-7) / 0.950"
Silver: / (4-9) / 1.020"
Black: / (5-9) / 0.950"
Blue: / (8-12) / 1.450"

dc2x4drvr

My motor runs at 10" vacuum, and I run a black (5-9) spring, quit worrying and enjoy the drive

jensenracing77

I talked to the dyno guy again. He said Sparky's builds way to many carb to second guess him. He said I may have a little less economy but will still work. He said let Sparky build it exactly how he wants it and it will likely be just fine. He said he can get softer springs to match the vacuum but maybe Sparky's has had issues with them.


With it being a 455 I don't think economy is anything I am worried about. As long as it is better than 10 MPG on the highway I will be happy.

Koda

Jensen, from what I have read about the 2 barrel jets being used in the w-30s, ie, no power piston or primary rods, I think WOT behaved the same, idle and off idle was the same, and it was the transition to part throttle that the car jumped a bit more.

However, I am sure you can make the piston work with your needs with the proper spring.