90 hp Johnson alarm

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twotexaslions

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Mar 28, 2011
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I am looking at buying a fish and ski boat with a 90 hp Johnson dont know the year off hand, we checked the gas,oil and ect. then put the muffs on it and started it up and ran it. The moter sounds great and the water pump is pumping, so we took it to the river to water test it. We warmed it up then backed it off the trailer and took off and an alarm went off and wouldn't let us go full throttle, the motor sounded great and there was water coming out of the discharge hole, I did notice that the water coming out of the hole would every once in a while stop and then start again, the water looked like it was strong coming out, need some help please.
 
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imokintex

Cadet
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Oct 14, 2010
Messages
20
Re: 90 hp Johnson alarm

On some models if the oil pump presure gets to low it will go into a low RPM mode. Will not let you go over 1500 rpm.
Start the motor on muffs and run it for a few min and put your hand on the heads to see how hot it is. It should not be to hot to touch. If the heads are cool it is probably your oil system.
If you are mixing your gas and oil then let me know and I will walk tou through the next step.
 
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emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 90 hp Johnson alarm

You can have a strong telltale on that engine and still overheat. The telltale indicates water pump condition in the lower unit-not whether water is circulating properly thru the powerhead. If either of the two thermostats are malfunctioning, (stuck closed) one of the heads will still overheat. Once you get the stat housing apart, you might as well put two new stats in, so you know you are ok for the future. At least you know the hot horn works properly.
 
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twotexaslions

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Re: 90 hp Johnson alarm

Thanks everyone for the help, I will be going back down to check this motor out and see what can be done so that I can buy this boat.
 
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bob johnson

Rear Admiral
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Feb 25, 2009
Messages
4,306
Re: 90 hp Johnson alarm

can you clarify running the boat on the trailer before launching??

are you in the water ON THE TRAILER running the motor to warm it up???

or are you in the parking lot running the motor on the trailer , to warm it up?

what was the cadence of the horn?

constant?

or did it have a pattern?

bob
 
T

twotexaslions

Recruit
Joined
Mar 28, 2011
Messages
3
Re: 90 hp Johnson alarm

We ran the boat at the house with the muffs on and ran great, then we went to the boat ramp with it on the trailer in the water and let it warm up, warmed it up and pulled off the trailer and started out and wouldn't go [was in slow mode]. then the alarm came on and it was a constant buzz.
 
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bob johnson

Rear Admiral
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Feb 25, 2009
Messages
4,306
Re: 90 hp Johnson alarm

next time just start her up and head out...just stay close to the ramp....some boats will over heat just idleing...and when they get enough water pressure, they cool down...

your motor definately was overheating( constant alarm and SLOW mode)...we dont know why yet.... I would run the boat right away close to the ramp and bring an infared thermometer.... pop the cover and check the head temps

I really think you need a little more info before you make a move to replace stuff. Even if replacing the water pump is always a first step...

what is the model number of the motor???

bob
 
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