1990 US Marine Force 120 shuts off almost immediately

[snead26]

Hello,

I have a 1990 US Marine force 120hp. I have had the boat for a few months now. The boat was running fine, then on the last trip to the inlet, it became hard to start. In order to keep it running I had to quickly give it throttle, which I understand is common with the motor. By the end of our last trip, I ran the motor over a sandbar, and after killing the engine, was not able to start it again.

I got the boat back home. Now the engine will not stay running. The engine turns over, runs for between 1-3 seconds, and then very abruptly shuts off. I have since replaced the starter and starter solenoid for peace of mind. I have also checked the voltage on the cdi and stator. I verified the kill switch is working properly. I removed the carbs and inspected and cleaned them. I also checked all fuel lines and filters with replacement as needed.

The boat is using a 2 battery system with 2 brand new 625 CCA batteries. I use a spark tester and noticed that the spark in cylinder 4 is not as bright as the other 3.

The way the engine shuts off so abruptly reminds me of an electronic shut off or something. I have searched this forum for answers, but am now stuck on where to go forward.

Does anyone have any ideas?

Thanks

 

[foodfisher]

Re: 1990 US Marine Force 120 shuts off almost immediately

Clean spark plugs? Fuel pump diaphram.

 

[snead26]

Re: 1990 US Marine Force 120 shuts off almost immediately

Just replaced the plugs, and also checked the diaphram. Thanks for the input.

 

[foodfisher]

Re: 1990 US Marine Force 120 shuts off almost immediately

750 RPMs idling in gear and in water?

 

[snead26]

Re: 1990 US Marine Force 120 shuts off almost immediately

I don't exactly understand your question. Last time I had it on the water I could not get it to turn over at all. After doing the work mentioned in the initial post, it now turns on for 1-3 seconds on the rabbit ears. Every 3 or so attempts, it backfires.

 

[roscoe]

Re: 1990 US Marine Force 120 shuts off almost immediately

Idle speed rpm should be 750-800 with the engine running in water, not on muffs.

On muffs, idle should be about 1000 rpm.

Check the timing.
If it is off, then remove the flywheel and check that the woodruff key is not sheared.
Replace flywheel and torque to proper spec.
Set timing.

 

[Frank Acampora]

Re: 1990 US Marine Force 120 shuts off almost immediately

Check the two "M" terminals in the ignition switch. They are the stop circuit. They should have contiuity on stop position and be open in run position. Perhaps vibration is causing a short inside the switch.

If your 1990 still has white and blue in the cable, at the engine terminal board near the starter, disconnect the blue and white wires then see what happens. If the engine starts and continues to run, then there is a short in the stop circuit--white and blue wires -- somewhere between the terminal board and the switch.

Also check for a short or melted insulation where the CD box wires go under the flywheel.

 

[snead26]

Re: 1990 US Marine Force 120 shuts off almost immediately

Thanks so much for the input. I will check the stop circuit continuity as soon as I have some time to work on the boat. I will also check the woodruff key. These make sense since the issue happened immediately after I ran too shallow on an unseen sandbar and the motor took a lot of vibration.