Speedo Converter

[rx7pat]

A while back a bought a mechanical speedo converter from Demon Tweeks, but it has never worked smoothly, as the needle jumps about like crazy.

Anyone know where I can get a decent KPH to MPH converter, ideally with an extended cable rather than a single metal unit like this....

http://cgi.ebay.co.uk/Motorbike-Mechanical-Speedo-Converter-Km-hr-Mph-NEW-/330427730813?pt=UK_Motorcycle_Parts&hash=item4cef070b7d#ht_500wt_949