Mercury 240 efi stalls at full throttle

[boatlife$]

Changed all fuel filters an engine runs fine at idle an when I put it in water an start giving it gas then full throttle it once it plans out or sometimes before it, it just bogs out an goes to idle speed sometime it shuts off completely but most of the time it just goes into idle speed I just don’t understand why anybody can help me out

 

[Tim75]

Check fuel pressure while running. Fuel pressure gauge onto the "tire valve" on top of the vapor sep. tank (vst). Should be 36psi. Should remain steady, even at full throttle. Internal pump may be weak. or the vst internal fuel filter clogged. Regulator could be stuck causing too high pressure, and over-rich condition.

Are all 6 cyl's firing? Are all spark plugs hot to the touch?

At some RPM, the trigger base electronicly changes trigger coils. Have you checked the wires from the trigger? Some had pretty crappy insulation.

 

[Sportster-2001-951C-Stock]

Don't overlook the anti-siphon check valve on the top of the fuel tank pickup (assuming it has this check valve as most boats do), I find these clogged often. While you're at it, pay close attention to water and trash that might be in the tank as well.

 

[Sportster-2001-951C-Stock]

At some RPM, the trigger base electronicly changes trigger coils. Have you checked the wires from the trigger? Some had pretty crappy insulation.

This is a good point to look for. The trigger coil color can be a clue to identify the improved version (I can't recall the new color but red I seem to remember is the former?)

 

[boatlife$]

Check fuel pressure while running. Fuel pressure gauge onto the "tire valve" on top of the vapor sep. tank (vst). Should be 36psi. Should remain steady, even at full throttle. Internal pump may be weak. or the vst internal fuel filter clogged. Regulator could be stuck causing too high pressure, and over-rich condition.

Are all 6 cyl's firing? Are all spark plugs hot to the touch?

At some RPM, the trigger base electronicly changes trigger coils. Have you checked the wires from the trigger? Some had pretty crappy insulation.

I didn’t check fuel pressure I was thinking it was bad cause I took it apart an blew into an no air come out the other side I took apart the vst an the filter didn’t look bad. I changed all spark plugs I didn’t change wires cause I had to order them but the boat runs for like 1 minute full throttle an doesn’t sound like it’s mis firing then it the gas dies an it goes into idle well when I feel the motor lose power I put the stick back into idle an when I took out fuel filter I dump the fuel in a clear jar an it didn’t have no water. Now what is the trigger wire I don’t know what that is.. an to see inside gas tank it is very difficult cause it’s behind motor. Also I open up gas cap while running boat to eliminate having a venting problem an it still did same thing. Should I order a new regulator an a new vst fuel pump

 

[Tim75]

You don't want to just start throwing $ at a problem because pretty soon you will have thrown it all! Remember what a boat is..........

The trigger is under the flywheel. It "triggers" ignition system when to spark into which cylinder.

When you say "full throttle", what is the RPM? Really need that number. Is the engine RPM actually dropping or is the throttle 'drifting' toward idle? +

 

[Tim75]

Did you replace the fuel filter on the lift pump? Is your lift pump working? Is your engine-driven pump working? Have you checked the voltage on the vst pump? I don't remember the spec value, but it should be steady.

 

[dblackstone]

I would get the service manual for that motor. In the Fuel section there is a chart for trouble shooting and it lists of the items to check.

Very easy to go down thru them to figure out the problem.

Join as a premium member at least for a month and you can download it from this site.