Yamaha 90 AETO 2 Stroke Stator Assy CDI question

[Nightfisher]

Hello all,

I have a 2 stroke Yamaha 90 that I just had the head rebuilt on because cylinder #1 had a hole in it. Since it had been really bogging down, I had cleaned the carbs a twice prior to realizing I should do a compression check.

I got the rebuilt head back, then put it all together and went out for a day on the lake. The motor performed great.

The next time I took it out it acted pretty much like before the rebuild, bogs down when you give her throttle. I checked the compression and 1- 140, 2-130, 3-140.

I had a friend come over and he put a test light from positive to the three lead wires that come from the stator.

The first two wires lit up and dogged down the motor and the third wire (the red one) did nothing.

He said he thinks it is the stator assembly, or CDI module or ignition coils.

Does anyone have any suggestions on how I should diagnose this before throwing a bunch of parts at it?

...or do you know anyone in dallas fort worth that is good with this stuff that doesnt charge an arm and a leg for diagnosis?


I tried to attach a picture of the control box wires but it failed. The three wires in order from top right of CDI are Pink, Blue, Red

[boscoe99]

The stator is pretty easy to test. And it is not with a test light. Why not test the charge coils, the pulser coil, the crank position sensor and the CDI output per the applicable service manual?

Before I did any of those tests however I would mist some gasoline into the intake system at the time the motor bogs down to see if possibly the problem is fuel related.

[Nightfisher]

Thank you. I did just find a service manual and can hopefully figure out the places to put the volt meter. (pictures are hard to read).

I guess I need a gap tester also whatever that is.

[boscoe99]

Here is a link to a 90 two stroke Yamaha SM that might be easier to read.

https://www.vansoutboardparts.com/se...c-70c-90c/file

[holmen78]

I have the same manual and it is great to have when doing maintenance. However the color coding on the Elec section is unreadable due to low resolution scan. So if anyone has a higher resolution copy, it would be much appreciated.

[boscoe99]

Buy the manual from Yamaha and it will be crystal clear.

[panasonic]

I have the same manual and it is great to have when doing maintenance. However the color coding on the Elec section is unreadable due to low resolution scan. So if anyone has a higher resolution copy, it would be much appreciated.

Go to the link Boscoe supplied, the wiring diagram is plenty clear there....you can download it and print it off...

[boscoe99]

Thank you. I did just find a service manual and can hopefully figure out the places to put the volt meter. (pictures are hard to read).

I guess I need a gap tester also whatever that is.

A gap tester is a device that lets you see the spark that is being generated for the spark plug. Some are adjustable so that you can see how far of a gap the spark will jump.

https://shop.advanceautoparts.com/p/...E&gclsrc=aw.ds

It is possible to use the spark plug itself as a gap tester. Remove the spark plug from the motor. Reinstall the spark plug cap. Hold the side of the plug to the engine block. Crank the motor. If the ignition system is good you will be able to see a spark jump the gap in the spark plug.

[Nightfisher]

Thanks to everyone. The manual is much better. It looks like today may be nice enough to get outside and check it out a bit.

I spoke with a guy yesterday that had me test the overheat alarm and realized I dont have the buzzer. He suspects it may be running in limp mode.

He told me to try unhooking the pink wire from the cdi and see if that cures the problem... then track doen the pink wire issue.

Alternatively, when i told him how at high rpms in the driveway on mufflers it makes a vroom, vrooom, vroom sound I hadnt heard befopre he said it may be a bad rev limiter in the cdi and to unhook the blue wire to see if that may be the issue.

[boscoe99]

You need to take that motor to a good mechanic before something really bad happens.

[Nightfisher]

You need to take that motor to a good mechanic before something really bad happens.

good luck with that here in dallas fort worth.

just checked all the sparks and they are all good. Unhooked rev limiter wire and seems to have possibly fixed it.... going to the lake to see if it gets out of limp mode... if so I will need to find a new CDI module

[boscoe99]

There is no "rev limiter" wire on that motor.

There are wires from (a) a thermoswitch and (b) the oil tank sensor switch that will put the motor into RPM reduction mode. Pink wires they are. They can be deactivated as you wish.

Then buy and install the new CDI. Best price can be found at this website.

http://www.boats.net/parts/detail/ya...540-06-00.html

[Nightfisher]

There is no "rev limiter" wire on that motor.

There are wires from (a) a thermoswitch and (b) the oil tank sensor switch that will put the motor into RPM reduction mode. Pink wires they are. They can be deactivated as you wish.

Then buy and install the new CDI. Best price can be found at this website.

6H0-85540-06-00 YAMAHA C.D.I. UNIT ASSY

Thank you big time for your help.

That is what the guy on the rev limiter told me at first, then when he found out mine was a circa 1985 ish he said the oil thing didnt have a pink wire.

There is one pink wire coming from the harness and it goes to the CDI and two pink come out the other end to plug into a double on the temp sensor.

VERY WEIRD DEVELOPMENT: Took the blue wire loose and it started and didnt rev funny. Took took to the lake and it wouldnt even start...no spark.

Brought home and started fiddling with test light and cdi. Ran a ground test light to one of the blue pink wires and the engine started immediately. I have started and ran it several times in the driveway since without touching any test light wires to the cdi.

It will now start and run with or without the blue or the pink connected... Does it sound like my CDI is just on the fritz?

I hate to take it out and get stranded.

[Nightfisher]

Got on the water and it ran fine across the lake. *****ed around for 20 minutes and when i went to go fast again, it was in shut down mode.

Came home and took apart the harness and looked at ignition where the pink wire was not attached, just taped up. (new after market ignition switch)

(I dont have a buzzer installed , but ordered one. I tested pink wire circuit with light until then. )

When I joined the two thermo coupler wires together at the engine, the light lights up. When running with everything hooked up as it should the it does not light up.

If the pink wire is the only thing that can put it in shutdown mode, and I run it without the pink wire attached to the CDI.... and then it goes into shutdown mode....does that mean the CDI is going out and need a new one?

[boscoe99]

What is the serial number of your motor? It will begin with the number 6. For instance 6H1 ******.