15HP Mariner 2 Stroke Engine Problem

[rneurohr1]

I have the above, 1992 model, and it is behaving strangely. When I first start and run it, for about 10-15 minutes it runs great, no issues, then it starts to drop RPM, come off plane, and bog almost like it is running on 1 cylinder. I had the carb and fuel pump completely rebuilt in October, fresh fuel, fuel filter, new gas tank and primer. Plugs are cleaned. Might this be an electricl problem with an ignition coil? Sounds to me like something is warming up and once it is at operating temp, it does not work. As far as I know, the electrical system is still factory. What should I look for in solving this, I don't just want to start replacing parts. Please help.

 

[FLATHEAD MAC]

Re: 15HP Mariner 2 Stroke Engine Problem

Have you squeezed the primer bulb while the rpms are droping ? Possible fuel pump , how is compression and what do the plugs condition look like ??

 

[rneurohr1]

Re: 15HP Mariner 2 Stroke Engine Problem

No, I have not tried the bulb but I'm certain the fuel pump is not the issue as it was completely rebuilt in October by a Mercury dealer/service shop. Plugs are OK, have a bit of oil on them, probabaly should replace them as I don't know how old they are. Have not tested compression. If it were compression, wouldn't the issue be evident at the start?

 

[jerryjerry05]

Re: 15HP Mariner 2 Stroke Engine Problem

A comp and spark test is the first syep in diagnosing any motor.
Even if it's a lower unit problem,I doa comp and spark test.
My neighbor was running a 9.9 for a year with a plug wire off.So a test will possibly aleaviate any possible problems.
I'd check the pump again.The diaphram could be bad.One backfire or cough can rip the rubber.
Any inline connectors? The Ethanol(you in the US?)(profile)in our fuel ruins the rubber seals and allows air in the system.
Then drop the float bowl check for crud.
Then the electrical system.Get an inline spark tester and go for a ride.J