All testing that we have carried out to date has shown that once the pipes have been changed, with the std. head and cams (being the limiting factors) nothing has had any real impact worthy of mention. I have always felt that the 865 required top end attention to allow it to breathe even reasonably normally and nothing I have seen so far has changed this view.
The restrictions are,in order (in our opinion)
1. Pipes
2. Cams
3. Ports
4. Airbox
Improvements can be gained at any stage with an improvement in the compression and no doubt a carb change would have benefits depending on what stage the motor was at.
Tweaking with needles, jets etc. may give a mild improvement but dont hold your breath.
Cheers
Graeme
www.Thunderbike.co.nz
