General Category > Quadrajet Carb Talk and Tips

Testing power piston springs

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GSP7:
I tested Cliffs 4 springs , light blue, orange, long green, plain color, with the stacked quarters($.25) weight method on top of the power piston with each sprg. set in a stripped main body  8) ;D.

Vacuum test like above would be better though  8)

68rs/ss:
Interesting. How did you determine which spring to use in a particular engine? I am thinking you would need to choose a spring that would hold power piston down at cruise. Giving some throttle or increased load on engine would drop engine vacuum. Did you pick a spring that started to lift power piston as vacuum dropped or choose one that lifted after a couple of inch's drop of vacuum? I Had tried this very thing with a spare core , but did not have a motorized vacuum pump for constant vacuum other than a hand vacuum pump, which didn't work. Good stuff. Phil

Cadman-iac:
 Hi Mike,

 I could do that, it will take a while to get all the information and post it, but that makes sense. Better to share the information with facts and dispell the rumors.
 The only issue is how accurate my vacuum gage is.  Another thing that may affect the results between mine and yours and others is the altitude, I'm at approximately 4600 feet, so at sea level would that change the reading a bit? Just curious.
 I'll start on this tonight, good idea, and thanks for the table on the springs, that could prove useful.

 Gsp7,
  I've read about that method, but I couldn't relate the washer weight vacuum readings, they didn't really correlate to me.
 I can't recall where I read about the method I used, it may have been the same place I saw that washer idea. I had been looking at the digitalcorvettes website I found after asking a question on Google.

 Between them and Cliff's website I think you can find anything you need on a Q-Jet, but Cliff sells parts, they don't!
 
 I'll get back with what I find when I'm finished. Thanks for the suggestion.

 Rick

Cadman-iac:
Hey Phil,

 I have a vacuum gage installed in my Suburban and watched it as I changed throttle position while driving.  Taking the average cruising vacuum rate, and the lowest reading when going WOT, I chose a spring with a  maximum vacuum about 2 inches below the cruising rate, and just below the minimum vacuum at WOT, so the piston will raise completely at WOT but remain down while cruising.
 Up until I found these sites, I had to rely on what was in the carb when I started and hope it was correct.
  I wish I had known all this stuff years ago, it would have made my life a lot easier.

 Rick

Cadman-iac:
  Mike,

 One thing that I noticed while testing the springs was that some would read the same but look very different.
 I'll have to go through them to give you the  specs on them, but I didn't expect that.
 One had closely wound coils and short, while the other had wide coils and longer if memory serves. I can be more precise after I get the information compiled.

 Rick

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