Mercury jet 120 - Water sometime collects in cylinder

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Robert Alford

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I have a 2000 Bass Tracker with an inboard 120 jet engine. It runs well most of the time but on occasion the starter can not turn the engine. It is always the same thing, water collect in the bottom cylinder. What is you best guess at the problem, bad head gasket or cracked cylinder head or something else?
 
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Robert Alford

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Re: Mercury jet 120 - Water sometime collects in cylinder

Here is some information that may beimportant in helping. I have not experience the problem when I had the boat in the water. Only when I was using the manufacture's flush plug. Could this be causing the problems.
 
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Robert Alford

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Re: Mercury jet 120 - Water sometime collects in cylinder

Sir,
Not sure I understand you reply. I assume you have had some experience with Mercury jets. If so, any suggestions. I am also looking for a repair shop in the Gaithersburg/Rockville Md area.
 
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x1745

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Re: Mercury jet 120 - Water sometime collects in cylinder

I have the same problem with home water
make sure you have water pressure regulator install to control water pressure from your tap, pressure too high that caused the water flow in the exhaust valve

Just remove all spark plugs and clams the gas line
use your ratchet and socket to crank it from the fly wheel by hand until all water remove from the engine this will take 5-10 minutes

while you crank it make sure spray some oil inside the piston to lube
Afterward you can reinstall the spark plugs and start the engine without the water up to 5 seconds to dry out the piston

Don't use the dealer kit adapter unless you have the water regulator installed
 
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CharlieB

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Re: Mercury jet 120 - Water sometime collects in cylinder

Merc has used two different pump systems.

O/B's transom mounted with the San Leandro snail shell pump (which also have a conventional o/b water pump w/rubber impeller)

Inboard mounted O/B engines with a Berkley style pump

I assume you have the latter.

Your system does NOT have a conventional water pump, it uses water pressure from the jet drive to supply cooling flow to the engine.

Unregulated water pressure on the adaptor allows water to 'splash back' within the exhaust where the water stream joins the exhaust, water pressure and speed is substantially greater than the exhaust flow thus the water is able to 'splash back' and enter the exhaust port(s).
 
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Robert Alford

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Re: Mercury jet 120 - Water sometime collects in cylinder

I believe that both of you have hit the nail on the head so to speak. The information is most helpful. Thank you. Following the procedures above, I have stayed out of trouble. The only thing I have added is to shut the water of at the same time I am shuting the engine down.
 
MikDee

MikDee

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Re: Mercury jet 120 - Water sometime collects in cylinder

If it's like a jetski design, you must wait till the engine starts, before turning on the water,,,, and, turn off the hose first before turning off the engine, when done running.
 
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Robert Alford

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Re: Mercury jet 120 - Water sometime collects in cylinder

It is the same engin and pump used in some jetskis.
 
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Bilge Monkey

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Re: Mercury jet 120 - Water sometime collects in cylinder

Start the engine first, then turn on water.......turn off the water,give a rev then kill the engine. The exhaust is water cooled, and if the exhaust isn't blowing water out, it's collecting in your pipe until it runs back into your exhaust ports and into your cases. Just be glad it's fresh water and try not to do it anymore. It's not a jetskii engine it's only used in small jetboat's such as open sands, sea raider (searay), and the like. Be glad you got the 120hp cause the 90hp 3cyl is a dog esp if the wearring is worn at all!
 
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