I'll try the spark plug as thats nice and easy it's been off the road for a bit as it (aparently) needed a lot to get through mot (£160 inc vat!).

I've had my k2 crm250 for about 2 years. When I first got it It would easily do 80-90mph on the motorway but now I can only get 70mph flat out!
Just wondered if anyone had any ideas as to what might be slowing it down?
Also need a new front tyre what best compromise for on/off road?