Q jet info for all, power piston spring rating
 

Last night after nearly giving up on the web search for this info,( which is info I use to have stached away somewhere) I though I would post IT up here for folks.
This is the Rocchester part number, but far more important, the HG vacuum rating at which they start to let the Carbs power system come off the idle circuit.

7037734 14.4"

7032758 11.5"

7037305 10.6"

7036019 8.4"

7029922 7.3"

7037851 6.3"

I have somewhere a list of Carb numbers that tells which Carbs came fitted with some of these common numbers, if I turn that up I will post it also.

that's good thanks. do you have springe lengths for these spring numbers.

turns count?
spring force?
or where do i ref these part numbers into such specs?

No, but I think there may have been a color code involved also, but once a spring gets 40 + years old in regards to used carbs I do not think that would be of much use anyway!
Turns count? All things being = the less turns, the stiffer the spring and the higher the HG number will be.
Spring force? Don`t need it man, thats what the HG rating is for.

STEVE I HAVAN,T RUN A POWER PISTON & METERING RODS,IN 5 YRS IN MY gto, best secret i ever did so far. never a issue.

Steve, i would put it like this:

7037734 14-4"

7032758 11-5"

7037305 (black/brown) 10-6"

7036019 (orange) 8-4"

7029922 (blue) 7-3"

7037851 (yellow) 6-3"

giving the range were the spring operates.

I can add 7029529 (purple) 12-5" to the list.

Ah,thanks!

I got tired of guessing what performance the commercially available PP springs have so I created a spreadsheet that takes free length, outer dia., coil count, and wire diameter to calculate the spring rate. I then converted the rate into what Start and WOT vacuum points would be. I took some liberties with the calculations in that I don't account for vacuum leakage or non-linearities or temp effects. I did create a jig with a spare fuel bowl to actually measure the PP spring behavior as a function of vacuum in the PP bore and it correlates closely with the calculated. Sorry it took 10 years to answer your question.