140 i/o mercruiser problem at full throttle !HELP!

[port jeff boater]

i have a 1986 140 mercruiser i/o and at full throttle after about a few minutes there is a rattling and then the rpms drop and the boat slows down..when i bring the throttle down after a few secs i then give it full throttle and it goes fine again but after a few minutes i get the rattling back and then the engine loses rpms and slows down,, please help.. at 3/4 throttle it is fine and at low throttle it is also fine please help.. i went out on the 44th and got gas not at my usual station,, any ideas whats wrong? thanks

 

[SS MAYFLOAT]

Re: 140 i/o mercruiser problem at full throttle !HELP!

Your rattling noise is probably your engine leaning out from fuel starvation. Check your fuel filters/seperators and also your fuel lines where they connect. Loose fittings may not leak fuel, but under a vacuum they can draw air which will cause you to lean your engine out. Carefull because to much lean operating conditions will burn your valves. Not a Pretty sight! Good Luck