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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10898
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a 1987 Yamaha 70 hp outboard. It started hard then

Customer Question

I have a 1987 Yamaha 70 hp outboard. It started hard then when running would not charge the battery.the next time I tried to start it it would not start even with a would crank over fine but no appeared to have no spark.
From what I have read this could be a CDI unit or a charge coil.
Any ideas?
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.

Hello Pete. My name is Tan.

Disconnect the white wire on the CDI now check for spark. Do you have spark?

Do you have an ohm meter to test the charge coil? Measure between the brown and the blue wires from the charge coil under the flywheel Disconnect from the CDI module.

Post back with findings.

Customer: replied 1 year ago.
I will be back at the boat this weekend and get back to you.
Expert:  Tan replied 1 year ago.

The spec for the charge coil is 145-190 ohms. If the charge coil is in spec then chances are you have a bad CDI. To be absolutely sure on the charge coil we need to check voltage out put while cranking with a DVA adapter or a peak reading volt meter. The spec is 140 peak volts.

Here is a DVA adapter.

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