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| | | | Joined: Mar 2022 Posts: 12 'Bolter | | 'Bolter Joined: Mar 2022 Posts: 12 | I've made a mistake, I'm rebuilding a Quadrajet , (GM 1966-74 4001B) and I have apparently lost the Power Piston Spring. I swear I never even saw it. I can buy a new one for the low, low price of $9.50 plus $7.50 shipping, or... What I'm hoping is that someone has one laying around that can measure it and I'll go find one at NAPA for $3!!!
Any help would be GREATLY appreciated.
By the way, the carb is off a '73 Firebird. The truck has a 400 Pontiac engine in it.
1959 Chevy Apache
1955 Chevy 3800
| | | | | Joined: Feb 2016 Posts: 1,994 'Bolter | | 'Bolter Joined: Feb 2016 Posts: 1,994 | I can see if I have one in my parts box but just the length won't give you all the info, they are VERY light springs and calibrated for specific applications. OK, I went out to the barn and looked in several drawers but could not find a loose power valve spring. I would have to take a carb apart to measure one. You might be better off with no spring at this point as it will keep the primary rods in the lean cruise position, if you have a spring that is even the slightest bit too strong you will be in "power valve" mode all the time.
Last edited by 78buckshot; 04/22/2022 4:17 PM.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
| | | | | Joined: Apr 2005 Posts: 7,441 Bolter | | Bolter Joined: Apr 2005 Posts: 7,441 | If you have a carburetor shop anywhere near Whitewright Texas I bet they would sell you one.
Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne (Emily)
‘39 Dodge Business Coupe (Clarence)
“I fought the law and the law won" now I are a retired one!
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USAF 1965-1969 Weather Observation Tech (I got paid to look at the clouds)
| | | | | Joined: Jun 2004 Posts: 8,597 Riding in the Passing Lane | | Riding in the Passing Lane Joined: Jun 2004 Posts: 8,597 | I have one with the power valve, metering rods & pri. jets. (78). The spring measures 1 1/16 in long.
I can send all those or part if you want.
I wouldnot run without one. It will run crudy.
George
They say money can't buy happiness. It can buy old Chevy trucks though. Same thing. 1972 Chevy c10 Cheyenne SuperIn the Gallery Forum | | | | | Joined: Mar 2022 Posts: 12 'Bolter | | 'Bolter Joined: Mar 2022 Posts: 12 | Wrenchbender, I sent you a PM
Thanks to all of you
1959 Chevy Apache
1955 Chevy 3800
| | | | | Joined: Feb 2004 Posts: 29,851 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,851 | If you're not going to use the correct spring, might as well try one from a ball point pen. Stretch it to fit!  Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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| | | | | Joined: Nov 2002 Posts: 2,767 Carburetion specialist | | Carburetion specialist Joined: Nov 2002 Posts: 2,767 | There were at LEAST 4 different springs used by Rochester on the 1973 Pontiac carbs. Going from memory, they may all be the same length, but have different spring diameters, different number of turns, thus different operating characteristics. I'm with Jerry on this one; although it would be easier to leave out the spring AND the step-up rods, and pretend it is a Holley!  Jon
Good carburetion is fuelish hot airThe most expensive carburetor is the wrong one you attempt to modify. If you truly believe "one size fits all," try walking a mile in your spouse's shoes!The Carburetor Shop | | | | | Joined: Nov 2002 Posts: 2,767 Carburetion specialist | | Carburetion specialist Joined: Nov 2002 Posts: 2,767 | I realize you only asked about the step-up spring, but what is "GM 1966-74 4001B"???
Pontiac alone used 98 different Q-Jets from 1966 through 1974.
Jon
Good carburetion is fuelish hot airThe most expensive carburetor is the wrong one you attempt to modify. If you truly believe "one size fits all," try walking a mile in your spouse's shoes!The Carburetor Shop | | | | | Joined: Feb 2000 Posts: 5,228 'Bolter | | 'Bolter Joined: Feb 2000 Posts: 5,228 | Cliffs Carburetors, https://cliffshighperformance.com/product/quadrajet-power-piston-springs It will take some trial runs to get the correct one for your truck. Stock may not be right since the motor is a trans plant. Vacuum controls the power piston and metering rods, the spring fights the vacuum. Stiff springs can cause richer metering, light springs offer leaner mixtures, both will depend on how much vacuum the engine pulls and how you drive. Ideally you want the metering rods to pull out of the jet just enough to richen the mixture when the engine calls for it, not before. This set up is similar to a Holley power valve setup, both add fuel when the vacuum reaches a certain level. Holley made it easy and marked the power valves at the opening vacuum, 3.5 4.5 etc... Rochester makes us work for it. | | |
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