'95 Merc. 5.0LX with 380 orig. hrs. Runs at low speed, not at high speed. Why?

Question

I've installed new fuel filter, cleaned carb. filter, and installed new ignition coil on boat mech. advice. Still slows or dies at higher speed (3200-3500). There's no problem at idle or slower rpm (1000-1500)

Answer 1

sounds like lack of fuel-check the float levels in the carb and run a fuel pressure test on the pump-also see if one of your lines/fittings leading  from the tank to the fuel pump is sucking air in--hook up an inline fuel pressure gauge and see if pressure drops off over your3200-3500 rpm-check and see if a fuel line is collapsing or sucking air from somewhere-if all this checks out it is something in your high speed metering system inside the carb

Answer 2

could be a fuel problem but i would check the stator  it would do that too then if its ok change the fuel lines

Answer 3

It definitely sounds like a fuel problem.You say you have cleaned or replaced the filters,but have you cleaned the carb?

If not it may help.Also have you checked your fuel tank outlet?

There is an anti-syphon valve there and it may be sticking or

have something stuck in it.An easy check for the fuel pump is to hook up a remote tank and use an outboard squeeze ball and when you get it to the rpm where it is falling off,have someone squeeze the ball and see if it picks up rpm's.I would

check your anti-syphon valve first because they are a problem

Good luck.

Answer 4

Anytime you have this type problem, a marine mechanic would check spark first.  The electronic Ign system and the plugs (type) are the first thing I'd look at.  If that checks out, I always go to my shop fuel tank, and see if the engine runs with no problem.  If so, look at fuel pick-up,hose, check valves etc.  Then go to carb. paying close attention to the float settings.