power piston springs

[fat tony]

over the years i've collected many q-jet parts. i have many power piston springs, many of them brand new from GM.
but, i don't have any of the specs on these springs. opening & closing at what vacuum readings.
cliff, do you know of a way that these springs could be checked. i would hate to get rid of them if i could use them
as a tuning aid.
(if anyone else would like to chime in, feel free)

[Cliff Ruggles]

Difficult to actually check them.  The best way I know of is to put them in a test carb on a running engine, and put a cut piece from a drinking straw down thru the vent till it sits on the hanger arms.

Hook up a vacuum gauge to manifold vacuum.  At this point you can vary engine speed and vacuum, even retarding or advancing timing to see the cut-in point of the springs. 

I've also heard of folks modifying carb main castings and using a vacuum pump, a mighty vac wouldn't work as well as there is too much leakage beside the power piston.....Cliff