Loads of info on the XRV.org forum, they have a sub-forum for Dommie's.
http://www.xrv.org.uk/forums/forum.php
I'm having the same tick over problem and it seems to be attached to the clogging of 4 small holes in the carb. They sit in the carb body just the other side of the butterfly from the exit of the fuel air mixture screw.
I did a full carb rebuild and it has clogged up again less than 2000 miles later.
Also have you reset the valve following the instructions?
I could get my valve set correctly, so gave up and
I then found out that you need to rotate it anti-clockwise to get TDC or it engages an auto decompression do dar.