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Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 14299
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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I have an 1990 (+/-) 70 HP Evenrude outboard boat motor. If

Customer Question

I have an 1990 (+/-) 70 HP Evenrude outboard boat motor. If I start it and go it runs well. If I let it warm up it will only develop 50 to 60% power.
Submitted: 1 year ago.
Category: Boat
Expert:  Jason replied 1 year ago.
Hello my name is ***** ***** am I speaking with?
Steps 1 and 2 with any outboard troubleshooting start with checking compression with a compression gauge. And checking ignition coil output with either an adjustable gap spark testor, or a timing light. Is that something you are able to do?
Customer: replied 1 year ago.
Compression is fine. The plugs are fine. Ignition coils have been swapped out and work fine. Timing is okay. Please refer to my original question. It runs fine unless I let it warm up.
Customer: replied 1 year ago.
This is heat related.
Expert:  Jason replied 1 year ago.
Did you check spark output once the engine was hot and the problem duplicated itself? Electrical parts can work when cold, and fail when hot, and then work when cold again.
Customer: replied 1 year ago.
Yes all the plugs are firing when it is hot.
Expert:  Jason replied 1 year ago.
Okay, lets do another test. Take the boat back out and duplicate the problem. Then try these 2 things. 1. Pump the primer bulb over and over, will the engine pick up rpms? If no, is the bulb sucking flat or not reinflating on its own? 2. Push in on the keyswitch to activate the primer bulb. Let me know if either test yields a positive result, or no result, and we can take it from there.
Customer: replied 1 year ago.
The bulb is fine. if I push the key in the rpms drop then recover when I let it up.
Expert:  Jason replied 1 year ago.
What were your actual compression numbers?
Customer: replied 1 year ago.
I will have to do that test over the weekend. But why would the compression be a problem only after it warms up? that seems counter-intuitive.
Expert:  Jason replied 1 year ago.
Did you have any idea on the cutout diameter? Back in the day this boat was built there really wasn't standard sizes openings. But today there are.
Expert:  Jason replied 1 year ago.
I don't know what happened but that last message wasn't for you.
Expert:  Jason replied 1 year ago.
Does the alarm system work on the boat? When you turn the key to start, does it beep every time letting you know the alarm works?
Customer: replied 1 year ago.
I checked to see if the plugs were firing when it was hot and the problem was evident. they were all firing
Expert:  Jason replied 1 year ago.
Does the alarm system work on the boat? When you turn the key to start, does it beep every time letting you know the alarm works?
Expert:  Jason replied 1 year ago.
Good morning, it looks like you read my last reply and logged off. Did you try to send a response back, as I did not receive one.
Does the alarm work on the boat?
Customer: replied 1 year ago.
There is no alarm. There is on issue with compression. I did experience a jolt of electricity through the steering wheel and binnacle when the motor began to loose power.
Expert:  Jason replied 1 year ago.
That sounds like either the black/yellow stop wire is chaffed, and grounding out. Or the keyswitch itself is bad and allowing voltage to leak through it. What I would do is get behind there and locate the black/yellow wire, and see if you can see if it is chaffed through anyplace. If the wire itself looks good, replace the keyswitch. Does that make sense?
Customer: replied 1 year ago.
No, The Jolt was like from a spark plug wire. But I don't see any plug wires arching.
Expert:  Jason replied 1 year ago.
You said got a jolt through the control and the steering wheel, did I read you correctly on that?
Customer: replied 1 year ago.
and the shifter binnacle.
Expert:  Jason replied 1 year ago.
The only wire up toward the controls that carries any voltage that you can feel is that black/yellow wire. That carries upwards of 300 volts AC, which is a bit of voltage. It is very common for key switches to fail, and cause that voltage to leak out. And then obviously if the black/yellow wire is chaffed and touching any metal that would do it as well. The way the engine works is when it is running, the stator makes that 300 volts for the ignition system, but it also sends it up a branch wire. That is the black/yellow wire. And it is called the stop wire. When you what the shut the engine off, what you do is turn the key to off, and that takes the voltage on the black/yellow and it shorts it to gorund, stopping the engine, and stopping any more voltage from being created and sent down that wire. So that is where the problem lays, either in the keyswitch or the wire itself. Does that make sense?
Customer: replied 1 year ago.
It make sense, I will look at that.
Expert:  Jason replied 1 year ago.
You are most welcome and I would glad I could help. If you had a further question on the issue by all means feel free to ask. If not, Just incase you do not understand the way the website works (and some folks do not). You do have to put forth a positive rating in order for it to credit me for helping you. When ratings are not done, the website simply keeps your deposit and they will not credit me. The ratings box is located at the top of the screen. Please let me know if you run into any problems or errors when trying to do it or if you can not see it. If you do have a problem, just reply back "I rate Jason's service _______" and fill in the blank. Questions do not lose out, so if you have to come back tomorrow or next week with follow up questions to this you still can even after doing a rating. Thank you,Jason
Customer: replied 1 year ago.
I will let you know what I find with the black/yellow wire.
Expert:  Jason replied 1 year ago.
Sounds good, post back if it still gives you troubles.
Expert:  Jason replied 1 year ago.
Good afternoon. Just checking in. Did you still need help on the issue?
Customer: replied 1 year ago.
Today is a hot day and the motor will not develop full power at all. Are there any mechanisms that will limit the motors power if it is too hot?
FYI: I found no problems with the yellow/black wire.
Expert:  Jason replied 1 year ago.
No, no mechanisms. Are you still getting shocked?
Customer: replied 1 year ago.
Done. No compression problems. The coils are all putting out spark and the plugs have all been replaced and gapped.
Customer: replied 1 year ago.
new plug wires to.

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