Outboard Alarm Sounding at 3000rpm

[tjbulley]

I have just purchased a boat with a 1990 - 1992 2 stroke 75 hp Mercury engine. When I put it in the water it starts and runs well until I take it beyound 3000 rpm when the alarm sounds. At 3000 rpm is when the boat gets onto the plane. I have just had it serviced with a new impellor, water pump checked, temp sensor checked, all OK. Plenty of spark, compression good, water is strong from the pee hole. Please help if anyone has any ideas.

 

[achris]

Re: Outboard Alarm Sounding at 3000rpm

I'd be taking it straight back to the shop.

A couple of things that a lot of shops DON'T do on a service that they should:
Replace the fuel pump diaphragms (Critically important!!!)
Check and clean the poppet valve (this is likely your problem)

Chris......

 

[tjbulley]

Re: Outboard Alarm Sounding at 3000rpm

Thanks for your reply Chris. I have followed your adviced and put the boat back into the shop. They are going to do a water test on Monday, hopefully they will identify the problem. i will advise them tha they shoud check the poppet valve.

 

[tjbulley]

Re: Outboard Alarm Sounding at 3000rpm

I took the boat back to the shop and they have conducted a water test. The technician has determined that it is the temp sender that is causing the problem. I would be interested on how that they came to that conclusion, although I will see what happens when it is replaced.

Any thoughts?

 

[sschefer]

Re: Outboard Alarm Sounding at 3000rpm

I took the boat back to the shop and they have conducted a water test. The technician has determined that it is the temp sender that is causing the problem. I would be interested on how that they came to that conclusion, although I will see what happens when it is replaced.

Any thoughts?

Temp senders do go bad. I'd give it a 50% chance of being the correct diagnosis. I'm more with the poppet valve being bad theory.

 

[tjbulley]

Re: Outboard Alarm Sounding at 3000rpm

I have spoken to the technician and he has confirmed that the poppet valve has been checked during the service and is good so I am hoping that the temp sender is causing me the concern as the motor is not actually overheating according to the technician who conducted the water test.

 

[tjbulley]

Re: Outboard Alarm Sounding at 3000rpm

The sarger continues. Temp sender replaced, no joy. Back to the shop. The tech now believes there is an electrical problem with the wiring or something. When operating a temp gun was placed on the engine and operating temperature was normal. See what happens next, stay tuned...

 

[tjbulley]

Re: Outboard Alarm Sounding at 3000rpm

I have finally found the problem. The oil injection is not working propberly. When oil is mixed directly with the fuel the problem goes away. I intend to disable the oil injection system and mix the fuel in the tank.

Thanks to all for your advice and hints during this issue.

Regards and good boating

 

[achris]

Re: Outboard Alarm Sounding at 3000rpm

I have finally found the problem. The oil injection is not working propberly. When oil is mixed directly with the fuel the problem goes away. I intend to disable the oil injection system and mix the fuel in the tank.

Thanks to all for your advice and hints during this issue.

Regards and good boating

That doesn't make sense... There's nothing on the engine that detects if there is oil in the fuel... The only oil warning module is connected to the float switch in the oil tank. All it can do is tell you if the oil level is low.

Chris.....