| It's interesting that you got a dip in the horsepower curve at 9,500 rpm after you gas-flowed the heads. I suspect this is a resonance effect associated with the airbox volume. For example, the 748R comes with a larger (14 liter vs. 8 liter), two piece airbox. To accommodate the larger air box the 748R frame is also slightly different, so they're are not interchangeable with a standard bike.
You can test my theory by temporarily increasing the airbox volume, by lifting the fuel tank away from the lower section of the airbox on a future dyno run, or perhaps make one of your future dyno runs without the ITG filter (since it fills-up some of the airbox volume.)
As to the low rpm stalling problem, a too-smooth intake tract can limit the creation of air vortices that help in the mixing of the incoming air and fuel droplets. Unburned fuel that drops out of suspension acts as a damper on combustion. At higher rpms the intake air velocity is higher so it's less of a problem.
Keep in mind too, that intake air velocity and efficiency in filling the cylinder is also affected by the throttle body diameter. 748's use 48mm, 916 use 50mm, 996 dual injector use 51mm, and shower injector models use 54mm (with the 748R being restricted down to 48mm at the bottom of the manifold.) The early 748's came with 50mm throttle plates, but were restricted after the plates down to 44mm which is why a number of 853 big-bore owners have back-fitted 916 50mm throttle bodies.  |