Does anyone have solid technical info on why mazda changed the OMP mixing design on these carbs, from the early model oil mixing with fuel in the float bowls, to late model oil dripping onto the outside of the booster venturis and being mixed with with fuel from the accelerator pump.

The latter is obviously more direct and responsive to changes in throttle position, but is that the only advantage. One disadvantage I can see is that oil is only going into the primary ports, so you would need to run the later model manifold with cross cut runners to get some oil through the secondary ports, if this is even a concern.

 

i've seen it mentioned in the SAE papers, but they don't say why.