The Yanmar 4JH4AE in my Hunter sailboat is not starting easily due I believe to air getting into the system. If I open up the throttle and crank it for a long period it will eventually start at high rpm which is not good for a cold engine. I have tightened all the hose clamps on the fuel lines and see no visible leakage. My boat has an electric fuel pump which may be the problem. Any ideas?