Yamaha 85 aet ( 2002 )

[Raymondschoeman]

Hi All

My name is Raymond and I stay in Port Elizabeth South Africa.

I have a 5.2m inflatable boat with a 85 Yamaha.
The motor is a 2002 model. I had this boat for 3 years now.
The last year I noticed a small problem. The motor starts fine and idle well.
The motor idles warm when I park the trailer and then I continue slow speed from the launch out the river. Out on the river when I starting to speedup you can hear and feel that the motor is running on two cylinders only. The boat wont go on plane. I tried going back to neutral and start speeding up slowly again but with same result. When keeping the throttle halfway open for a couple of seconds the problem will go away and you can feel the power and hear the motor sounds good.

After that you can go to neutral and takeoff with no problem. When stopping for a short while and takeoff no problem. If I anchor and fish for a while I will have the same problem with the motor running on two cylinders. If you drive at idle speeds for a long period it wont come right. Only when you trying to speed up at higher revs the motor will come right.

I rebuild the fuel pump added a water trap. Had the carbs rebuild twice. Oil mixing ratio 50 to 1. Used new fuel. No difference between built in tank or plastic carry on tanks. Fitted new spark plugs.

Is there something I can try because the boat repair guys is making money and me losing. Please any advise or any thing I can try will be appreciated.
Regards.
Raymond.

[rodbolt17]

the US market in 02 did not have the 85.

there were two versions of the 90 ign system.
one used 2 pulser coils and a CDI pack.
the other used an arm that moved a TPS,a crank position sensor,mounted on the aft port side by the flywheel ring gear, and one pulser coil.

unlike some older CDI systems this uses one or two pulsers to trigger 3 plugs.
that third spark is triggered by the CDI internal circuitry.

so yes it is possible to drop spark on a cylinder.

only way to find it is with a peak reading meter or the Kv tester at the failure RPM and load.

[Raymondschoeman]

rodbolt17
Thank you for the quick reply. I believe this is an imported motor. On the Yamaha South Africa system this motor is a 2002 registered engine.

Can the spark be dropped every time on the initial takeoff. This only happens when the boat sat for more than an hour or so. If you move around every say 20 min the engine is fine with no problems. Only when you anchor for more than an hour and then move the motor will run on what I think two cylinders for a couple of second at half throttle and comes right with the third cylinder coming in and then is fine until you anchor for longer periods.

Thanks
Raymond

[rodbolt17]

again. I have NO literature on NON US market motors.
the AET indicates its an international market and the US did not get the 85 after about 96.

I have no idea which ign system yours uses.
but most likely it will be based on one of the US market 90 motors.
the 90 used 2 different types of ign triggering.

but if you suspect an ign problem its going to have to be tested at the failure RPM and load.

like I say, if it runs well while my gear is on it I cant tell you what to replace.
that does happen.
runs great for me, then the customer has issues and I test it and it runs great.

there have been issues with both Yamaha and Volvo that took months of playing before the issue was found.

[boscoe99]

What is the primary ID for the motor. It will begin with the number 6. Perhaps we can find a USA equivalent.

When Rodbolt says it is an "international" engine he means that the specific model (85AET) was not offered here in the USA.

Yamaha USA only publishes information to its dealers and customers here in the USA that pertains to the models that are offered here in the USA. For instance, if you look at the Yamaha USA parts catalog you will not find a reference to an 85AET model.

Is your motor the premix or oil injection type? Here in the USA a C85 was offered which could very well be similar to you motor. Just need to know your engine ID to verify this.

[99yam40]

being the motor does this every time when motor cools off, it should be easy to do some testing to see if spark it being lost.

Maybe you can use a timing light clipped on the individual plug wires while the problem is there to see if they are all getting spark.

It may not tell you if one is getting lower voltage though. That is why it would be best to test with the proper test equipment like Rodbolt said.

At 1st I was leaning on it being a fuel pump leaking into #3 crankcase causing a miss fire until high RPM cleared the cylinder enough to get the fuel to air mix where it would burn, but you said you already rebuilt the pump.

does this motor have a choke or is it a prime start enrichment system?

But you need to make sure spark is good on all cylinders while problem is there before chasing a fuel problem

[Raymondschoeman]

Hi All

Here is the detail of the motor.

85 AET
688 L 447039

Hope this help.

Regards.

[Raymondschoeman]

Hi All

Thank you for all the replies.
The motor is the premix model.

Ho can I maybe test if the fuel pump does or not leak into #3 crankcase.

Regards.

[boscoe99]

Your motor should be 99% one and the same as the USA 1996 model C85TLRU. Based on this maybe Mr. Rodnut can provide you with some specific things to test, and how to test them.

How are your troubleshooting skills? Best of luck to you. Finding intermittent faults can be a chore.

[Raymondschoeman]

boscoe99
Thank you for this information.
I can do some testing but for electrical I'm useless.
Can a electrical fault cause a problem just for a while and disappear and return while one is on anchor for a while.

Could you be so kind to email me a manual that I could read and learn more about this motor. I have looked all over and cannot find anything on the aet model.

Regards.

[99yam40]

Hi All

Thank you for all the replies.
The motor is the premix model.

Ho can I maybe test if the fuel pump does or not leak into #3 crankcase.

Regards.

As it has been said test spark /voltage 1st so you will know if it is good on all points and cylinders while problem is showing up

[boscoe99]

boscoe99
Thank you for this information.
I can do some testing but for electrical I'm useless.
Can a electrical fault cause a problem just for a while and disappear and return while one is on anchor for a while. Yes. Dammit!

Could you be so kind to email me a manual that I could read and learn more about this motor. I have looked all over and cannot find anything on the aet model.

Regards.

With respect to a manual for your specific model you will need to contact a Yamaha dealer in your area. It won't be available from here in the USA.

If you can't obtain a service manual locally then you can always procure a printed copy of a C85TLRU manual from Andy at www.simyamaha.com

Unfortunately the Yamaha manuals are intended for use by a trained Yamaha mechanic and can be difficult to use by a non-Yamaha mechanic.

For parts procurement or to visualize all of the components of the motor you can look at the C85TLRUS parts catalog. Here

http://www.boats.net/parts/search/Ya...LRU/parts.html

[Raymondschoeman]

boscoe99
Thank you very much. I will try and test and come back with more or new info.
Do I need to test all electrical test what you have sent me.

Regards.

[99yam40]

I have a feeling you do not have the test equipment to do the electrical testing, but if you can, test the peak voltage out of the CDI.
If not in spec then check the inputs to CDI


I would start with a inductive timing light to see if it shows spark on all cylinders while the problem is happening.
Or use an inline spark tester to watch what the spark is doing

[Raymondschoeman]

Hi All

I had a autolec tested all electronics and all equipment was in spec.
Do you guys think a carb can cause this problem.

Regards