I have a 1984 inline 6 90hp merc that when I run it on the lake will run up to its max rpm of 4500 for the length of time it takes to go about 1/2 mile and then the rpm drops to 3000. if I pull the throttle back for just a second or to after this happens it goes right back up to 4500rpm for another 1/2 mile. Doesn't help to squeeze fuel line bulb when it happens , cap is off of fuel tank any Ideas?
