If anyone's got the mikuni manual handy there's a formula in there where based on combustion chamber volume,etc etc it outputs I believe a good ballpark jet size to start from for a given engine configuration...

-e

Eric,

Just been flicking through these posts for info on 40phh models and came across your unanswered post.

From "How to modify your Nissan/Datsun OHC engine" by Frank Honsowetz on page 111.

"For an initial main-jet size, start with 0.04 the size of the main venturi. Eg, if a 40mm main venturi is used, install a 1.60mm main jet, or 40x4 divided by 100 = 1.60mm For an air-correction-jet size, add 0.20 to the initial main-jet size. Eg, install a 1.80mm air jet, or 1.60mm + 0.20mm = 1.80mm"

Not too sure if that helps you any?

Anyway you have probably sorted it already!