97 115 Johnson Faststrike (One hot head, one cool head)

hemiman40

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Feb 17, 2009
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The first time I took my boat out this year, I started having problems with the rpm's fluctuating at high rpm's. It idles fine, once on pad and increasing through the rpms, it starts to surge and decrease until finally stalling out. I can idle around fine and at low rpm's. I have recently been out of town for a month and just got around to diagnosing. During my first diagnostic session, I could not even keep the motor idling (wasn't doing this on the water). I worked with it several times, and this past weekend I had my father come over to look. It continued to act like fuel starvation as it cut off after idling for a few minutes. Cranked up again, and the starvation problem is gone, will idle fine for as long as you want. However, when reving in nuetral it still starts to fluctuate around 3000-3500 rpms and won't hold steady. We did notice that the passenger side head was not hot to the touch and you could keep your hand on the head. However, the driver side head was extremely hot and you could not keep your hand on it very long. I checked the spark on the passenger side and it is fine. The only thing we noticed was the cam follower sleve was dry rotted on the linkage (i have ordered the part). Any ideas on the heads and could this be causing the problem? Thanks!!!
 

tashasdaddy

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51,019
Re: 97 115 Johnson Faststrike (One hot head, one cool head)

you have a thermostat in each head, sounds like one is sticking, motor running hot on that side. remove the round plug on the upper of the head, and change tstat. you need your model # to get the correct parts.
 

hemiman40

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Re: 97 115 Johnson Faststrike (One hot head, one cool head)

Thanks, I looked up the part on evinrude.com. I found the thermostat assembly for my model number. What other parts are needed to complete the swap? I am going to order it, but wanted to see what else I would need to along with the assembly such as the spring, etc. Thanks again
 

tashasdaddy

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Re: 97 115 Johnson Faststrike (One hot head, one cool head)

you need the seals/gasket for the tstat also.
 

hemiman40

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Re: 97 115 Johnson Faststrike (One hot head, one cool head)

Thanks again,one more question. My model number has a C suffix. On evinrudes website, it shows that C suffix require only one thermostat, while A suffix model numbers require 2. Is this correct? Thanks again
 

crazy charlie

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May 22, 2003
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5,581
Re: 97 115 Johnson Faststrike (One hot head, one cool head)

There should be a very large plastic black Cover on the top of each head.Looks like a big bolt head.Open them up and have a look.I believe there are 2 .Charlie
 

hemiman40

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Feb 17, 2009
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Re: 97 115 Johnson Faststrike (One hot head, one cool head)

Well, the cam roller wasn't the problem. I still have a miss above 2500 rpms. The Thermostat is next. Any other ideas about what may be causing the propblem? I have checked off the fuel system, replaced lines, pump working properly. I am stumped if it is not the thermostat causing the passenger side bank to run lean. Help!!!
 

ezeke

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Sep 19, 2003
Messages
12,532
Re: 97 115 Johnson Faststrike (One hot head, one cool head)

What's the model number of your motor?

You should have S.L.O.W. warning system on your motor which would cause the irregular running at higher RPM when the engine overheats on either bank. When an engine overheats it can bind the pistons and stall the engine.
 

James R

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Feb 1, 2007
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2,679
Re: 97 115 Johnson Faststrike (One hot head, one cool head)

Have two motors here and the only thing I can find that may have caused failure is the the intake manifold joints were leaking and allowing air into the cylinders on that side. This would mean that those cylinders were running lean resulting in overheating. Try the bolts on that side.
 

hemiman40

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Feb 17, 2009
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Re: 97 115 Johnson Faststrike (One hot head, one cool head)

Well the thermostat was not the problem. The fuel pump is working properly. I have read some previous threads about the sending unit in the tank. They were having the same symptoms I am having. Bulb losing pressure, engine bogging down. Any thoughts?
 

mike-seanymph

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Apr 23, 2009
Messages
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Re: 97 115 Johnson Faststrike (One hot head, one cool head)

I have the exact same problem with my 1996 115hp Johnson Fast Strike. Ran great since 1996. Replaced the water pump a few years ago and thermostats too. Ran the engine both with cuffs and in the creek and the port side thermostat housing is way to hot and the starboard side housing is way to cold. These thermostats both function normally years ago and I checked them often. Tonight I removed both stats and checked them on a stove in hot water and they both opened around 160 degrees. I put both back and even swtiched them around and the port side head is still way to hot and the starboard way to cold. Engine has only 250 hours in 13 years. I am original owner and this engine always ran flawlessly. Any ideas? I know for a fact that in prior years both heads always felt about the same temperature. Thanks for any advice !
 
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