PMO air corrector jet question

[jameshtaylor]

The PMO's on my 2.7 run a bit lean at high rpm under load with AFR's in the 13--13.5 range. CORRECTION. Tried 145 mains then reverted to 140's after finding car way rich in midrange.
Air correctors are 190's. I'm thinking I should be using 180's or 185's to get the AFR closer to 12-12.5 at the high end. Anybody know what sort of AFR shift I can expect as I move from 190 to 180?

[Frank Beck]

Not much.

Size of PMO's and venturi size would help. And what's "high" RPM?

[jameshtaylor]

PMO's are 40mm with 36mm venturis...high rpm means over 5500 to 7k on this engine.

[1QuickS]

Classical relationship between main jet size and air corrector size is: a change up in mains of "5" is equivalent to air corrector change down of "15".

135s are leaner than 140s so a change up in size would be richer.

36mm main venturis with S cams & sport exhaust would typically ask for 145 to 150 mains & 170 air corrections in Webers.

As John Passini would say "Suck it & see".

[jameshtaylor]

Paul. Thank you. See my correction above... I found 145's too rich in midrange, not 135's (which were too lean.)
I'll try 175's and see how I do. Are the PMO and Weber air correctors interchangeable?

[1QuickS]

I think PMO & Weber share common idle jets but the main circuit jet stack design is taken from the IDF Weber family and are not interchangeable.

The smaller main jet and smaller air correction should fatten the upper range without causing a rich lower end...Suck it & see.

[Norm01]

The PMO's on my 2.7 run a bit lean at high rpm under load with AFR's in the 13--13.5 range. CORRECTION. Tried 145 mains then reverted to 140's after finding car way rich in midrange.
Air correctors are 190's. I'm thinking I should be using 180's or 185's to get the AFR closer to 12-12.5 at the high end. Anybody know what sort of AFR shift I can expect as I move from 190 to 180?

Is 13-13.5 at high RPM under load really considered lean. I would of thought this to be perfect a little rich of 14.7.

[jameshtaylor]

Middle 12's is where most of the experts seem to want the car to be under wide open throttle.