Don't know if you're still having trouble with the mixture leaning out before the PV kick in. But like Davenc was saying, that might be the cause of the 0.039 HSAB's you're running. Standard HSAB's are much smaller at 0.033. A too large HSAB leans out the mixture at higher flows.
Have a look at this graph. Pics are always clearer than words.;)
So you might have to go with smaller HSAB's to keep it from going lean at medium acceleration. The lean mixture should also show up at cruise with higher loads or rpm.
