Yamaha 90 Engine power drops after 20mins

ArraMusha

Hi,

I have a Yamaha 90 2-stroke that runs fine for 20 mins then drops power by about 20%.

Advise I got was that this engine senses if the engine oil is low and limits power to 'get you home'. So after topping up the oil to full I noticed the 'dash' dial still showing oil at half and the same problem occurred with the engine dropping out.

Is this a common problem with the yamaha 90's? Could it be the oil level sensor? I haven't opened it up yet.

If anyone has come across this problem can you please advise what could be the problem.

Thanks
Jim.

breghall

I'm taking it that you don't premix the oil and petrol together ? but that you have two tanks yes?

fergal.b

Depending on the year a model of your engine check the float in the oil tank is moving up and smoothly and all ground connections are good also check the oil filter to see if it's blocked.
The thermostat can also put it in safe mode so just feel the engine and look for steam out of the pee hole just incase, and just on the off chance check the air breather on the fuel tank is open and there are no kinks in the fuel line.:)

tin79

Assuming its an auto injection - we had the same problem with our suzuki last year. Removed the oil tank and there was an amount of 2 stroke gunge in the bottom which was clogging the oil flow. Removed and flushed the tank, filled up with new oil and it did the job. Clean the float switch while you are at it.

but it could be several things as Fergal said so you might need to do some detective work.

ArraMusha

Thanks.

Yes it has its own seperate oil tank its a 2006 engine with low hours.

I will take it off and check the float is operating OK and give it a good cleaning and see how that goes...

Will let you know how it goes tomorrow...

Daibheid

Best engine ever made IMHO and give very little trouble. I've had two of them and they never gave any trouble with the oilong system and I'd be surprised if such a fresh engine had a load of gunk in the oil tank.

I sounds more like fuel starvation to me so I'd check the obvious stuff - breather open, no kinks in the fuel line, the underhood filter is clean and if there's a water-separator in the system that it's clean and full of only petrol.

You don't mention service history - has it had a set of plugs in the last year or so? Always a good start with a hiccuping 2stroke.

You should look at the plugs anyway and see if they're showing signs of oiling and lay about the engine with WD40 on anything with a wire coming off it.

ArraMusha

Thanks for the advice...

Right, so I emptied the oil tank, removed the oil level sensor and all looked ok and freely moving i.e. no gunk. I followed the wiring back from the oil level sensor and noticed the earth or ground wire (blue) from the sensor not connected...also the pink wire from the sensor was badly corroded at a joint.

Cleaned the joint, connected the ground, and put the oil tank back in. Then as I started to fill back the oil tank the buzzer on the dash went off (it was buzzing beforehand) and the oil level now shows full

Testing her tomorrow in Connemara hi tide 18:30. Pictures to follow...

fergal.b

Sounds good, best of look tomorrow.




.

breghall

hope it goes well and if it does you'll always know what to check for in the future if it ever acts up again. oh check and maybe replace the filter too.

ArraMusha

No joy!

After about 10 mins it dropped again in power

I'm thinking now it temperature related? as it starts out fine and can handle the high revs and then drops.

Anyhow, I'll firstly follow the advise from 'fergal.b' and 'breghall' above and check filters, new plugs, air breather etc.

I don't have a manual, it's a recent purchase, so I'll have to google the location of the thermocouple(s) on the engine. Might be a job for repair shop, but I spent so much time on it now I'd hate to give in to that...if you know what I mean.

By the way, water is coming out the 'cooling' hole so no blocks there.

...onto google...

fergal.b

Sorry to hear that, this may help a bit. http://www.yamaha-motor.com/assets/service/manuals/1/LIT-18626-07-12_1406.pdf

And this is a breakdown of your engine parts the thermostat is number 41 in cylinder & crankcase.
http://www.boats.net/parts/search/Yamaha/Outboard/2006%20and%20Later%202-stroke/90TLR/parts.html




.

breghall

It may be temp related and the motor is going into SLOW mode which is there to try and limit damage to an engine in an overheat condition. Check your thermostat and even your impeller (although you are getting a pee stream) and replace them if they look anyway poor.

tin79

Try here for really cheap PDF manuals. I have used this site a few time - works spot on!

http://www.readmanuals.com/outboard.motors/yamaha/

ArraMusha

Changed the spark plugs, filters, flushed the cooling system. Changed the petrol tank with new petrol and primed it, making sure of no kinks. After talking to some people who know Yamaha engines they advised that the thermostat would definately not cause the problem so I left it alone. When for a spin.

Noticed that it was OK, very slow to respond i.e. then I pushed the lever forward there was a delay of a few seconds before power arrived, then it went fine loads of speed and was fine for about 20 mins. We stopped for a few seonds and then when went goin again and it would not rev up like before, coasted back to base.:o

Had a look again to see if the rev cable was opening the levers fully in the engine and it was. So not a rev cable problem.

The latest thought is fuel...?

It'll be 2 weeks before I get to go out again, plenty time for thinking..

breghall

Did you notice if you had a good strong pee stream all through the ride??

If not temp related and it ran ok for 20 mins I'd rule out fuel as it was getting fuel for those 20 mins. My next line of thought is electrical, some parts like coils or cdi power packs can fail when up to operating temp. If you know some one with an inductive timing light , borrow it and next time your prob arises whip off the cowling and check to see if you have a weak or intermittent spark by attaching it to each plug lead and checking the strobe light. If you can't get one just try pulling off a plug lead to see if there is no change in performance when acting up and if not then this is you prob cylinder. Oh and don't fall in while doing this (has to be done when moving on the water) and use a heavy rubber glove or pliers so you don't get a shock..

ArraMusha

There was a steady pee all the time.

I'm planning one more test then I'll suggest the test above to a mechanic close by that I heard was good.