My son was riding the 90 along a good road up and down hill at a constant speed of aprox 30km for 10km durning warm weather and the bike got hot and shut down. Now we can not get it to start at all The oil in the bike smell a little burn so we change it to new oil. The moter turn orer good and it has good spark and gas. compression seams fine as this bike only has 585km on it. One bike shop said the culch is gone not letting the motor to spin fast enough to start. could this be right.

 

I am no expert, but if you have gas and spark and it is not firing then the next thing I would check would be compression. Just because it has a low amount of km on it does not mean the compression is good. You could have fried a ring.