Does anyone know what the factory stock primary jet size is for the '83-'86 L-69 cars?
Was there a difference between that and the size used in LG-4 cars?...

 

I am NOT an authority on this but as to my knowledge from reading and the few ccc carbs I've dealt with, the primaries were very similar if not the same. Passages all seem to be the same vain, very close if not identical. Secondary rods and hangars where richened up on L69 cars so it seems. Makes enough sense I suppose.
But all that isn't verified nor worth anything even if 100% true. Factory could easily do anything they wanted whether any documentation said one way or another. What's in there and what makes it tuned best means way more.

 

Not sure how much this helps, but my 83 G20 305 was a 73 jet, 50M rod, DR secondaries and F hanger from GM. Been a while since I have been in a Chevy CCC Q-Jet but my Vin9 Olds 307 had a 72 jet. Jets seemed to be in the low 70s on the 5.0L engines. Even the dual jet on the 350 in my 80 C10 was jetted with 72s and a 46m rod.

 

I just happen to have '84 LG4 and L69 carbs apart at the moment. Both use the same primary 76 jets and 57U rods. Secondaries are richer on the L69, J hanger with DR rods vs M hanger with CH rods on the LG4.

 

Started to ask what the power tip diameter was but answered my own question. Find it odd how much richer the primary side is on those than my non-cc. The trucks had a 0.036" power tip vs the 0.026" on those 57Us.

https://quadrajetparts.com/used-quad...ds-p-2658.html

 

Remember, the MCS is ticking half of the time to lean the mixture.
If not that, then maybe the massive power of the 305 with it's factory 3/4 race cam requires so much extra fuel?

BTW, the 350 HO conversion also used DR secondary rods, but I can't remember which hangar.

 

My stock 305 was DR with a F. The 73 with a 50M that used a 0.036 power tip always felt lean until the secondaries opened up. Probably the reason it got very good highway mileage back in the day when I had the APT adjusted just to the point of lean misfire and then backed out a 1/4 turn from that point.

 

I am told that my current non-CCC Q-jet has 62S primary rods (.036 power tip) and 72 jets...