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Sounds like a coil problem

T

Tim Murray

New member
I have a 2001 90 horsepower Honda 4 stroke outboard. Engine runs around 5500 RPMs when it's cold but when it warms up it shuts back to 4750 RPM and runs sort of rough. Any advice or help would be appreciated thanks
 
It may or may not be a coil.

Next time this happens, have someone go back to the engine and pull the choke out a little...then a little more to see if the engine picks up. If it does, then it is a fuel problem.

If that just boggs the engine down, then take a timing light and connect it to each plug wire, one at a time. Make the engine fail and observe what the light is doing on each cylinder. The cylinder with the odd light flicker is the troubled cylinder. At least, that will give you a place to start.

If you think you have a bad coil, checking resistance and comparing the two will also help narrow it down.

I am assuming you do not have a kv tester to check the actual voltage at the spark plugs. If you do, comparing the voltage reading will also help.

All that being said, hopefully, you have already changed the spark plugs and are using NGK DR7EA and no other brand or plug number. A spark plug could be breaking down.

I have had this happen to me and it turned out to be the ICM. I already did the carbs (at the customers insistence...even though I told him it probably was not the carbs) , isolated the fuel system and checked out all the electrical parts.

I just happened to have a test ICM and stuck it on the motor when we got it to fail.

It is also possible that the fuel system is sucking air. The time that it takes to do it may just be coincidental with the time it takes for the motor to warm up.

One last thing. Check the temperature at the thermostat with a hand held temp gun to be sure that it is not over heating.

As you can see, it could be any one or more of many things. You just have to eliminate those parts that are working and narrow it down to the one that does not.

Mike
 
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