i have a 93 mercury 40 hp classic that i got last year and the problem is when i'm in the water at full throttle it will lose power to about half throttle but then it will surge every now and then. i replaced the fuel filter. what else can i do? the motor sat for four years before i gas it with no gas in it. and started right up when i was looking at it before i bought it and it ran fine for five outings before i had this trouble. i'm not real good at motor work of any kind can someone please help?