Outboard won't spin unless spark plugs removed.

[boater12345]

Hey all,
I have a 2003 Mercury 125hp 2 stoke. I started it up earlier this summer and ran it for a bit. Since then I have not had the time to use it and it sat for a few months. I tried to start it the other day and the starter spun fine (did not start the motor the first two tries though, figured since its a two stoke thats been sitting it'll take a bit of time), I went to prime the fuel ball and when I tried to start it again all I got was a slow and prtt, prrtt prtt. It sounded to me like a battery problem so I hooked it up to my car battery and am having the same problem. I took out the spark plugs and the starter works fine (spins the flywheel fast) when the spark plugs are in, I am able to spin the flywheel by hand but with some resistance.

I did some research and according to the internet my starter is either bad or I have water in my cylinders.

Any ideas?

 

[CaptnKingfisher]

Hey all,
I have a 2003 Mercury 125hp 2 stoke. I started it up earlier this summer and ran it for a bit. Since then I have not had the time to use it and it sat for a few months. I tried to start it the other day and the starter spun fine (did not start the motor the first two tries though, figured since its a two stoke thats been sitting it'll take a bit of time), I went to prime the fuel ball and when I tried to start it again all I got was a slow and prtt, prrtt prtt. It sounded to me like a battery problem so I hooked it up to my car battery and am having the same problem. I took out the spark plugs and the starter works fine (spins the flywheel fast) when the spark plugs are in, I am able to spin the flywheel by hand but with some resistance.

I did some research and according to the internet my starter is either bad or I have water in my cylinders.

Any ideas?

I suspect loose connection. Check starter selenoid and starter wires. Disconnect the battery to avoid shock, remove and clean wires with fine sandpaper or Emery cloth. Spray contact cleaner and reinstall. It takes nothing for your starter to spin the flywheel with the plugs out.. the fact that you can turn it by hand with a little resistance tells me all is right. Your starter could be bad, but I suspect loose connection or your battery is no good.

You can also do a voltage drop test on the battery. Hook up your multimeter to POS and neg on battery and test volts while cranking. Voltage will drop when you crank the engine but should not drop below 9 volts. If it does replace battery

 

[Chris1956]

Check the starter wiring for dirty connections or rotted wiring. If most of the battery cable is rotted away, the starter can spin fast and then slow down rapidly, like the battery is bad.

 

[Scott Danforth]

Agreed, clean all battery cable connections