Mercury Sport Jet 120 problems with new starter

[Lucas Neves]

I'm having a hard time dianosing a problem with the starter on my Mercury Sport Jet 120 xr2 (year 2000). The starter was having a hard time turning the engine: it would turn it slowly, often getting stuck.
Since then, I have replaced the battery, the power cables, the solenoid and the starter itself, but the new rig still has the same problem. The new Quicksilver starter, connected directly to a new, charged battery through new cables, is still unable to make the engine spin. It engages the flywheel, sometimes revs the engine once or twice, and gets stuck.
Can it be that the engine itself is somehow too hard to spin? I am able to turn it by hand, but it does take a lot of effort to make it spin.
I don't know what else to test. This is my first boat, so I'm still learning everything. Any directions would be much appreciated.

 

[jcyamaharider]

I would pull the park plugs on the engine and see if it gets easier to turn over by hand. IF this is hard to spin by hand then I think you may have found the problem.

 

[Lucas Neves]

I would pull the park plugs on the engine and see if it gets easier to turn over by hand. IF this is hard to spin by hand then I think you may have found the problem.

Thank you for pointing me in the right direction!

After pulling the spark plugs, the engine was very easy to turn over by hand. When turned, the lower cylinder would spray out water. After getting rid of most of the water, I was able to start the engine

Now, the question is: where is the water in the bottom cylinder coming from? I am working with two possibilities:

• I have been tanking with gas with ethanol. There is a risk that the ethanol is capturing moist from the air and creating a watery phase on the bottom of the gas tank, that gets sucked in the engine; or
• The water may be getting inside the cylinder when the engine is flushed with tap water after use.

I'll test both cases and post my conclusions here for future reference. If you have any other thoughts, please let me know.

 

[jcyamaharider]

I would run a compression test now and then run a compression leak down test. Glad it worked out for you!!

When you flush the engine with water it is running correct? General rule of thumb with our Yamahas: Engine on then Water on. Water off then engine off.

 

[Lucas Neves]

I would run a compression test now and then run a compression leak down test.

I ran a compression test right after pulling the spark plugs, but I think the test was compromised by the water in the cylinders, at least in the lower one. The readings were 145, 145, 140, 185(!). I will redo the test.
I don't know how to perform a compression leak down test, but I'll look into it!

When you flush the engine with water it is running correct? General rule of thumb with our Yamahas: Engine on then Water on. Water off then engine off.

The service manual for my Mercury Sport Jet 120 does not mention turning the engine on for flushing, so I leave it off. I read somewhere that, for this model, the flushing kit might not provide enough water to cool it down. Should I really turn the engine on for flushing?

Thanks!

 

[jcyamaharider]

Not too familiar with your motor but if we do not do it with the Yamahas we will fill up the cylinders with water.

Compression sounds good, just rerun like you said after all of the water is out.

 

[Scottintexas]

Lucas, did you see we have a dedicated sugar sands section? it's ok to post in the general but in the future you may get more sugar sands eyes on it there,
@Bilmon sorry to @ you again but your the only one I remember that owns one, can you confirm the hose flush procedure,

 

[Bilmon]

No first hand experience with the 120 but it looks like that's how the 120 manual reads. No danger of pumping water into cylinders on the sportjets. Probably safer that way, the old 120/90 sportjets were know to blow the ride plates off by backfiring and igniting unburned gas in the exhaust system when shut off @Scottintexas no problem .willing to offer what little help I can

 

[Cobra Jet Steering LLC]

Those do not need to run when flushing because it is an outboard power head sitting on top of a jet pump Not sure why he had water in the lower cylinder I read that and just scratched my head in wonder.

 

[Manfred]

I'm having the exact same problem, I almost ordered a new starter. Glad I read this. I will pull plugs and see the difference. I still didn't understand how water got into Lucas motor. Hopefully that's my problem. I just got the boat and dont know the history.