it has done this off and on the past few weekends but eventually works. when i crank the boat it will only crank and then when key is returned to on it dies. if i hold the key in the crank position it stays running (only did that for a second or two). i have ruled out the ignition switch, the oil preasure sensor, and the kill switch. it is obviously getting fuel,air,and spark bc it will stay running in the crank position. what is the problem?