I have an '06 trx450r stock and it is hard starting once in a while. Most of the time it will start normal but once in a while it will ot start with out a pull start. I crank it over and the tone of the motor is different, just about like there is no compression. It will do it either warm or cold. I am sure it is the decompression vale doing it but what might cause it to stick open or is it something else? It has never acted up at home so I could find the problem. Spark is great, fuel is good, compression is perfect.