How many times has this happened? Just once, or many times? What was the weather like when it did this? Please post more details of motor, year, model, etc.
You should be working with a manual.<br />Have you checked the kill switch?Is there spark?<br /> If Im reading my manual correctly the motor could have one of 2 types of ignition.Standard magneto with points or cdi with points and external coils. I believe the mag.uses a kill switch.The cdi uses 12 volts from the battery via the key switch..Check for 12 volts at the cdi with the key on.<br /> When checking for spark you should use a plug with the the ground electrodes removed and well grounded or the cdi may be damaged.
