Thought I'd share this with you guys out there. In my earlier post, I mentioned that my throttle cables were over 5" too long and the grip wouldn't snap back quickly at any handlebar position, and thought that the problem was the way I'd routed them.
Well, thanks to certain responses from some of you guys, I had a think and realised one thing I hadn't checked out was whether the rubber hand grip was clearing the right hand switch unit - I'd previously bought a new grip and stuck it to the plastic throttle pipe with epoxy adhesive. But I'd stuck it on too far along so, surprise surprise, it was rubbing against the switch unit. So after stripping it out and trimming off some of the rubber so I could see a little daylight between thr grip and the switch, hey presto! I have a throttle. And even despite the cables being too long (these loop up under the tank). Thanks Honda but no thanks. It's also important to remember that the throttle grip and switch unit are not secured to the handlebar so that the inside of the grip rubs against the end of the handlebar.
I hope this will be useful to anybody with similar throttle problems - sometimes the simplest answer to a problem is the least obvious!!