Oh, Erm, I'll stick my photies on from here then.
Here's the standard throttle tube measuring at 37mm dia which gives you about 1/4 turn.
This is the piece I cut out of 35mm pipe, the walls are about 2.5mm thick. I just cut it so as it fitted on the throttle tube like this.
Once glued in place, I cross drilled and glued some 2mm nails in just to be safe.
Once the glue dried, I trimmed them down with a file, and cut some slight grooves in each end near where the cable nipple runs.
Once this is done, you need to gently remove some metal from the two lugs in the housing, but just enough to allow clearance. It's only a couple of mm.
The cable guides needed the ends chamfering slightly, to allow the tube to run free.
Once all put back together, it has reduced the throttle turn by just enough to make it 1/5th. (you might be able to make out the marks I made before I removed it.
C'est voilla! All done for Bugger all!