19 HP Kawasaki FH601V engine hp upgrade?

[clif]

OK I have installed this throttle shaft, now my engine idles at 3550 rpm, pretty much wide open. How do I get it to go back to 1550 rpm, like it was before swapping throttle shafts? The idle adjustment screw on the carburetor (the one right next to the throttle linkage cable and throttle shaft) does nothing, since this is only a stop for the throttle shaft and the throttle shaft won't close very much even when throttle lever is set to slow idle.
There is that screw that's mounted on one end of that throttle cable/ choke cable control plate, it is very difficult to access, nearly impossible short of removing the entire engine. I guess it has something to do with that governor shaft. If this isn't it, does anyone know other ways to lower my idle speed?

For people that have done this upgrade already, have you had to make adjustments to lower the idle speed after installing the new throttle shaft, if so what did you do?