Primary jets and rods size

[GSP7]

Original carb on my 1981 chevy k20, 350 sm blk, auto trans(4x4 3/4 ton pickup) is #17080513

Primary jets are 72 , rods are 51m ( I documented those sizes years ago when  I rebuilt the carb)



I have another Carb I am rebuilding for this truck #17080213 (it has bronze brushed throttle shafts done already)

Primary jets are 73, rods are 49m  (maybe off a 454 cu in ?)

Isnt this 17080213 carb going to be alot richer with those 73 jets and 49m rods ?



Book specs says the 1780213 should be

Primary jets 71, rods 50m


I would like to get the book spec, 71 jets, 50m rods to install in it

Is this correct thinking

[GSP7]

PS, 73 jets are larger than 72 jets....

what about rods size differences? Is a 49m rod going to be richer than a 51m rod with same size jet?


In other words is the rod numbering, smaller the number = smaller rod ?

....and what's the "m" stand for?

[Kenth]

17080213 mfd by Carter has #73C jets, 49M primary rods and DR secondary rods from factory.

17080213 mfd by Rochester has #72 jets, 50M primary rods and DP secondary rods from factory.

17080513 mfd by Rochester has #73 jets, 50M primary rods and DR secondary rods from factory.

The suffix "M" on rods tells you it has .036" power tip and the numbers indicates the size of the upper part of the taper in thousands of an inch.

Also, i have found that Carter jets with suffix "C" measures dead on the size in thousands of an inch while Rochester jets, #71 and larger, often measures one or more thousands of an inch larger than the stamped number would indicate.

Conclusion, you are fine with the present jets and rods in your carbs using the APT feature in these carbs to set the final cruising mixture.

HTH

[GSP7]

17080213 mfd by Carter has #73C jets, 49M primary rods and DR secondary rods from factory.
(My Carb with this jetting has "Rochester Quadrajet" cast in to the left side)

17080213 mfd by Rochester has #72 jets, 50M primary rods and DP secondary rods from factory.

17080513 mfd by Rochester has #73 jets, 50M primary rods and DR secondary rods from factory.

.... .....

Conclusion, you are fine with the present jets and rods in your carbs using the APT feature in these carbs to set the final cruising mixture.

HTH

My original to the '81 truck carb 17080513, Calif smog motor, has original factory #72 jets, 51m prime rods, DR secondary rods

That's different than your above sizes. Why does mine have smaller jets / different size rods? Is that factory designed leaned out for calif emission tests?

Is a jet #73, rod#50m carb a richer running, than  jet #72, rod #51m carb?  Just curious for Knowledge

I live in Idaho now so no smog test

Thanks

[Kenth]

In theory, yes, if the rods are set at the exact same height in the jets.
But,it depends on how the adjustment of the APT, Adjustable Part Throttle, is performed.
The result of this adjustment may be the same regardless of the examples of your jets and primary needles.
At WOT a #73 jet will be richer than a #72 jet