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2000 90hp 4cyclinder Johnson Outboard

Sam Johnson

New member
Having problem that motor will not turn more than 3000rpm's under load. Also when running on the muffs at 2500rpm's every now and then the motor will sputer and drop down to 2000 rpm's for a moment and them return to 2500rpm's. Motor has not been run much in the past two years. Have replaced spark plugs, cleaned fuel filter, checked the spark plug wires and everthing seems to fine. The engine starts and runs at low rpm's very well. Any ideas as to what might be causing the engine to run this way?
 
Motor will not run idle right on the water hose, the motor needs back pressure ( to be in the water) to make it run smooth..... is the motor going into S.L.O.W. mode? is the motor overheating? what is the motor doing when you are trying to run under load?
 
Motor will not run idle right on the water hose, the motor needs back pressure ( to be in the water) to make it run smooth..... is the motor going into S.L.O.W. mode? is the motor overheating? what is the motor doing when you are trying to run under load?
it is always best to start out with the basic,s first 1) get an accurate compression check please do not assume or skip this step a standard 90hp should have = 110-120 psi if the compression is more than 10psi less than your highest reading your motor in all probability not idle right. but if the compression is fine then you may want to have your carbs open up and inspected. most people don,t know this but it only takes about 28 days for the carbs to start(gumming) you need to start and run you motor at least once every 3weeks to keep the fuel/oil mixture in the carbs from varnishing, if you let this happen month after month the gumming will plug the jets located in the bowls of the carbs and keep you from idling right . This will also lead to a lean fuel/oil mixture and cause motor damage or failure. now contrary to what most folks think there is no fuel conditioner out there that you can use to clean this condition out of your carbs they must be open and cleaned. i have only seen a very few times that someone had success with fuel additives. 2) if you suspect the S.L.O.W system to be the problem then try this, while standing behind the motor and looking at the engine with the cowl off, located right next to both top spark plugs you will find a lite tan wire w/blue stripe unplug the wire, there is usually one on each head but not always. 3) if non of the above works then it is possible that your stator is going bad and unless you have a marine fluke meter with all the right attachments you will have to take it to a shop to have it tested. this is assuming that your motor is a 2 stroke and not a 4 stroke. anyway i hope this helps
 
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