I realise that I've sort of hijacked his thread at this point, since Nate's "Flying Bicycle" is up and running again, but I'm still confused regarding the idle position for the throttle arm.
On my 4600, a spring holds the throttle arm at its lower limit - won't go no further. When I roll the throttle handle on the handlebars, it pulls on the throttle arm (against the spring) which increases the RPMs. "At rest" the spring pulls things back to the lower limit. This is where I would expect some sort of idle adjustment device to come into play, but there doesn't seem to be any.
I'm missing something somewhere...
PS - I did clean some crap out of the carb filter - thanks for the heads up there.