89 75hp merc

[axiosteve]

89 75hp merc... wot hits 2500 rpm or less feels boggy when driving into wind... sounds like it runs good tho???

 

[Mi duckdown]

Re: 89 75hp merc

IS your tach correct? what GPS speeds are you getting?

 

[CharlieB]

Re: 89 75hp merc

Your motor should operate within 4800 to 5200 RPM at WOT.

It may be possible that the high speed windings of the stator are not generating sufficient voltage for the ignition to allow the motor to make power above 2500 RPM.

NEVER ASSUME any electrical parts is bad, there is NO RETURN on electrical parts.

Study the section on your ignition in the (free) CDI Electronics Ignition Troubleshooting Guide

CDI Electronics Practical Outboard Ignition Troubleshooting

Use a DVA Meter or a DVA Adaptor along with any Volt/Ohm Meter to test the stator.

 

[axiosteve]

Re: 89 75hp merc

the tach is an old analog so maybe its bad. But i can gwt it to high rev neutral at 3000 rpm. My gps speed is about 25mph

 

[CharlieB]

Re: 89 75hp merc

Analog tach's are OK, it is very important that the load on a well tuned motor allows that motor to operate within the specified range at WOT. If over-loaded it will radically shorten the life of the motor.

There are guys in the Prop forum that can calculate your boat, size, weight, etc., and give you a prop pitch recommendation, however, the first thing they will ask is if your compression is good, ignition hot, both at low and high speed, and that your fuel system/carbs are clean and adjusted properly. Which is the reason I recommend DVA testing the stator, reduced output from the high speed windings will not create sufficient voltage to fire an arc across the increased cuy pressure of WOT, the engine power and speed will be limited to under 2500 RPM.

No load, even a weak ignition will rev the motor high enough it can grenade and blow the rods out the sides.

Test and PROVE the stator good/bad.

 

[axiosteve]

Re: 89 75hp merc

Well I just had it in a shop for stalling when putting into gear... they said all the test were good and rebuilt the carbs and changed plugs. Idk exactly what they tested but it dose drive now just at 2500rpm.. im going to test the stator.

 

[GA_Boater]

Re: 89 75hp merc

Are the carbs fully open?

 

[axiosteve]

Re: 89 75hp merc

Are the carbs fully open?

You see that's what i was thinking
Im not even sure... im new to outboards and Idk what linkages open what?? How can I tell

 

[GA_Boater]

Re: 89 75hp merc

Push the remote control fully forward, get a light and look in both carbs inlet for the butterfly to be at right angles to the inlet. You should see the edge of the butterfly.

What is the serial number of the motor?

 

[axiosteve]

Re: 89 75hp merc

ill get the serial up tomorrow, yes the carbs are open, how can i test for a high speed missfire?

 

[CharlieB]

Re: 89 75hp merc

Re-read my post #3

Ignition voltage will limit power and speed up to the point the ignition does not have enough voltage to arc across the gap, the motor will not pull any faster.

An inductive pickup timing light may fail to flash regularly when the motor hits this condition, yet the light should flash perfectly at lower speeds.

Because there is NO RETURN on electrical parts you want to test and re-test to prove a component bad before ordering a new part.

A DVA meter or a DVA Adaptor for a Volt/Ohm meter should clearly prove the stator output at cranking speed, check both the low speed and high speed outputs to the switchbox, compared to the values stated in the CDI Guide.

 

[axiosteve]

Re: 89 75hp merc

What are all the components that could be problematic in my case?

 

[CharlieB]

Re: 89 75hp merc

Most likely, the high speed windings in the stator.

Study your ignition, testing, and values here

CDI Electronics Practical Outboard Ignition Troubleshooting

But remember, test, test, and test again to PROVE the fault, there is NO RETURN on electrical parts.

 

[axiosteve]

Re: 89 75hp merc

ok so i got the year wrong. Its actually a 1984 75hp. if that makes a diffrence. I hoping its just a stator.

 

[CharlieB]

Re: 89 75hp merc

Merc replaced the distributor with the ADI switchbox and stayed with that ignition until switching to the current CDM.

You still need to PROVE that it is the stator high speed windings.

Your stator is three sets of windings, low speed, high speed, and battery charging.

One other slight possibility, a charging problem caused by a bad rectifier can cause a disruption of the magnetic field and reduce high speed voltage. The test is to disconnect and tape off the two yellow stator wires that connect to the rectifier, run the boat and see if the motor will pull under load to WOT. If so, replace the rectifier. If not, then DVA test the stator high speed windings.

 

[axiosteve]

Re: 89 75hp merc

Thank you charlie for all the help. Ill be running some test. As soon as I get a chance.