Thanks guys for all your comments. I would make the following observations.
My machine was out of warranty when I did this mod.
Regardless of what everyone assumes about belt life, mine was clapped out after 7000 miles, teeth gone from rear sprocket, teeth worn out of shape on the belt and belt stretched
Total cost was just over £200 plus labour ( of love ) and this will be the case at every replacement due to wear and tear - so a cheaper future than the original.
The noise and jumping still exist and I am trying to get some help from Centa regarding the possibility of the problem lying with their coupling - watch this space.
Sorry if my input is a bit erratic but life and other work keep getting in the way!
