Here's some more. The software I used for this is free:
http://audacity.sourceforge.net/ Just get a recording of the bike, listen for a few seconds of smooth idling, and then zoom in on that part of the sound until you can see the individual putts as the tall lines. Stick the numbers in (putts ÷ seconds) x 2 x 60. The more time you count for the more accurate the reading.
http://www.youtube.com/watch?v=3Oi4xoFdjdI (the one that sounds like your bike) is actually quite fast at around 1560
http://www.youtube.com/watch?v=tSfnEqnXT_Y (with the very blued pipe) is obviously too slow, around 900 rpm. A little tricky to count since it is misfiring sometimes.
http://www.youtube.com/watch?v=1yH1NmQSP6w is about 1360
http://www.youtube.com/watch?v=9oHIJJtbo1A is 1880
It would be nice if someone with a tach could post a recording along with the tach reading so we can triple check all this.
In my case I got it set to about 1200, but feels like it will stall every time I clutch & let off the throttle. The revs dip dangerously low for a moment and then bounce back. I guess I need to do some carb work.