Changing the Main Jet and Air Filter made no difference to the top speed of the trike.  Acceleration was possibly a little better, but that was good before the changes, and the fuel consumption was terrible - around 3/4 of the tank (probably about 1 1/2 gals unmeasured) for a 38 mile run.  Compare that to about 60mpg before.

I think that the only way to get more speed out of this system is to do something radical to the CV system.  I'm open to any suggestions from anyone who has actually modified their CV system on a 250cc engine on a trike or ATV, and got better that 50mph max.  Anyone out there?

The trike is still fun to ride, and cruises really well at 30-50 mph.  I would just like to get it up to 60mph, without spending vast sums to get there.  Otherwise, I'll continue to enjoy riding it as is.