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1990 evinrude 120 cuts out

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kherby1

Member
I have a 1990 evinrude 120 that has not been run in 7 years
Put new plugs , impeller, t-stats , and linked and synced carbs
Motor runs great but overheats and alarm goes off after 4-5 minutes above 4000 rpm
Keep it below 4000 rpm and it runs all day without overheat
Only the starboard head sensor goes off
Any suggestions on this would be great but my real question is : The instant that the overheat alarm goes off , the motor bucks like its missing badly and the rpm's drop instantly
are the overheat sensor and the powerpack related at that time to protect the motor ?
Once it cools down it starts right back up and runs great until exceeding 4000 rpm
Always run in fresh water ( Montana )
 
OK
Researched some more and found that it goes into SLOW mode and cuts out fire to the plugs opon overheat to that particular head
With that being said , is it possible that i received a bad new T-stat?
It seems to me that the vernatherm / T-stat only does its job at low rpm , and at higher RPM the T-stat actually lifts off its seat and much more cooling water flows around the T-stat to allow more cooling at higher RPM / heat build.
I thought maybe the control valve was not doing its job and blocking inward water pressue that would allow the t-stat to lift off its seat , but if that was the case , the port side t-stat would not lift either and it would also overheat , but , right now only the starbord side is overheating
 
Easy to test. Pull the thermostat and put it in a pot of water and heat it up. Should open around 160, I believe, maybe 180. There is also a very small hole in the center of that gasket that must be clear. A couple of other things that makes one side heat up are deformed or out of place water deflectors, or not getting fuel/oil to a cylinder, or poor pressure. Just because water is coming out of the tell tale does not mean it is flowing properly around the cylinders. One last thing is a bad head gasket.
 
Was the rest of the waterpump in good shape?
Did you reseal the housing properly?
It takes waterpump pressure to open the pressure control valve.
 
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