Purchased the 250 at Xmas 2011 and since new after riding for 10/15 minutes as you accelerate it looses power and stalls. I had problems at 193kms after taking to a mechanic he cleaned carbie etc and suggested there was excess oil on air filter. Bike went well until the other day at 427kms. It should not happen to a new bike. Local mechanics are puzzled. Can anyone help?