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Testing power piston springs

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Cadman-iac:
  Since I have an extensive collection of QuadraJet parts, I figured it would be nice to know exactly what the springs where rated so I could make an informed decision about which one to use.

 On another forum I found a lot of information on Quadrajets, and they explained how to test your springs so you could figure out which one to use.
 They recommended using an old core body and applying vacuum to the base of the piston bore.
 So I took a core and pressed a 90° plastic vacuum connector  into the port for the piston, used some long 5/16" bolts to keep it elevated so the fitting was not being pushed to either side, and I connected a vacuum gage with a "tee" fitting,  a vacuum source with another "tee", and a valve that can open and close with a turn of the knob to create a controlled leak.
  I used my A/C evacuation pump for the vacuum source, and after putting the spring I wanted to test in the bore I installed the power piston and turned on the vacuum.  Using the gage to tell at what vacuum the piston begins to move downward by slowly closing the valve to change the amount of vacuum applied to the piston, I was able to accurately determine at what vacuum the piston begins to move and at what vacuum it reaches maximum travel. Then I wrote that down and bagged it for later use.
 I tested over 70 springs like that and I now have a collection that has 19 different settings from 2-6"HG to 9-16"Hg. The first number being the minimum vacuum required to move the piston, the second number being the maximum vacuum required to fully seat the piston.
 Once I determine what vacuum the engine achieves at idle and what it makes at cruise speed, I can pick the best spring to use in the carburetor.

 Here's a few pictures of what I used. The valve is a simple rotating type I think was for an aquarium or something.
 Hope this helps if you are wanting to test your springs so you know what you have on hand to tune with.

 I also used this method to test the vacuum advance unit on the distributor.  It helps to know how much vacuum it takes to get maximum advance and when it quits.

 Rick

novadude:
Nice idea!  if you have tested the commonly available springs from cliff and others, can you share your results? 

quadrajam:
Yeah, what novadude said.^

Cadman-iac:

--- Quote from: novadude on January 31, 2025, 05:46:26 AM ---Nice idea!  if you have tested the commonly available springs from cliff and others, can you share your results?

--- End quote ---

 Novadude,

 I have only found out about Cliff's website from browsing through answers to questions I posted on Google, so I wasn't aware that you could buy parts from him. I found his book in a bookstore years ago and have been using it, but I confess I hadn't thought to look for parts sources from the book. I've always done things the old school way, I'd go to the parts store. It's only been recently that I've started looking online for answers and parts.
  I used to be a partsman at a GM dealership for years so I had gotten parts through them. I bought 3 10 packs of springs over 30 years ago and still have probably half of those left, plus what I've pulled from my carburetor collection. I've been retired for 20 years, so I guess you could say I'm outdated now.
 Unfortunately I don't have any way to tell if any of the springs I have are equivalent to what Cliff offers. If you have an old core that you can use to test with, you can use your engine as a vacuum source with a long hose going to your test carb if you don't have another vacuum source you can use.  You will need a vacuum gage of course. The valve I used is for an aquarium or I think it might be for a drip watering system. My son and I were doing a hydrogen experiment for one of his school projects many years ago and we had bought a bunch of tees and valves for the project and I can't remember where we got it,  maybe Lowe's hardware? Since then I've been using that stuff for all kinds of things. One valve was used to regulate the vacuum to an EGR valve when I was having some issues with bucking on another truck. I've been collecting parts and vehicles for 50 years, so I have a bit on hand, and I have the space to keep it. You might say I have my own wrecking yard.

Shiny:
Rick, that's a labor of love that could genuinely help a lot of people if you were willing to share.

I understand it would be difficult to assure apples to apples, but if you're willing, pull out your calipers and add the spring dimensions to your table.  For example, if you add the length, coil OD, the wire diameter, and the number of turns, it would be relatively easy to match across different sources.  There are online calculators that could even estimate spring rates.

I've attached a table I used when I was trying to make a reasonable guess on selecting a PP spring.  I don't know where it originated, but someone like you did a lot of similar work and tossed it into the ozone.  Thanks to the originator and perhaps it may help you.

I used the same approach as you on both my distributor advance and on the needle/seat holding power against fuel pressure (trying to diagnose a flooding/nozzle-drip issue).

So I like your effort to actually quantify these things!  Beats the heck out of folklore!  And with the chaos in the aftermarket parts world, my confidence in the distributor advance specs was sketchy at best.

Mike

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