First off your cam is to small the Rotax engines that i had worked on were only in the 670 cc range and required a cam with 270 degrees of duration @.050 judging from your flow figures your going to need a cam with 260 to 270 degress i also stated in here that average port velocitys should be in...
I have had good results with single and twin cylinder engines by keeping the average intake port velocities around 360 to 380 fps based on port cross section .do every thing you can to keep the port straight to reduce localized velocities .
The spiny lock system has been replaced by a rough bumby iron surface on the twin cams . i beleive that the spiny lock introduced some cylinder distorsion to the evo cylinder you could always see a shiny track where the cylinder studs were located sugesting that these areas were protruding @...
