yamaha 2.5hp stopped on a hot day

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RichardtheBoffin

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I took my 2.2m dingy out yesterday, with a 2.5hp Yamaha 4 stroke on. This is the first time I've used this motor in earnest.

It has been run up in the tank and once I cleared a blocked jet, it ran perfectly.

Out on the river yesterday (ambient 30 degrees C!), it ran fine for about 40 mins, at very modest throttle (4 knot limit), then for no apparent reason, it just stopped. No spluttering or warning, it just stopped.

I could not start it again, even after waiting 10 mins.

I did notice a slick of fuel or maybe oil on the water when I tried to re-start it.

Once home again (after paddling to the river bank and a long walk back!) the motor ran fine in the tank.


The tell tale was showing plenty of water while on the river and is was coming out cool.

I don't know if these motors have a thermal shutdown, but the slick on the water was clearly showing a problem.

I don't think the motor should have overheated but I did wonder if the fuel might have gotten too hot and vapour locked?

I will run a whole tank of fuel through it in the tank just to see if I can repeat the issue.


Any ideas what may have caused this issue? Are small 4 strokes renowned to pack up after 30-40 mins on hot days?
 
No they should not stop. If the engine still will not start check basics. Compression, fuel and spark. If it has compression and a good spark your issue is fuel based. Make sure fuel is getting to the float bowl . If fuel is in the bowl have another look at the carb.
 
RichardtheBoffin said:
I took my 2.2m dingy out yesterday, with a 2.5hp Yamaha 4 stroke on. This is the first time I've used this motor in earnest.

It has been run up in the tank and once I cleared a blocked jet, it ran perfectly.

Out on the river yesterday (ambient 30 degrees C!), it ran fine for about 40 mins, at very modest throttle (4 knot limit), then for no apparent reason, it just stopped. No spluttering or warning, it just stopped.

I could not start it again, even after waiting 10 mins.

I did notice a slick of fuel or maybe oil on the water when I tried to re-start it.

Once home again (after paddling to the river bank and a long walk back!) the motor ran fine in the tank.


The tell tale was showing plenty of water while on the river and is was coming out cool.

I don't know if these motors have a thermal shutdown, but the slick on the water was clearly showing a problem.

I don't think the motor should have overheated but I did wonder if the fuel might have gotten too hot and vapour locked?

I will run a whole tank of fuel through it in the tank just to see if I can repeat the issue.


Any ideas what may have caused this issue? Are small 4 strokes renowned to pack up after 30-40 mins on hot days?
Click to expand...

Stopping suddenly makes me suspect an ignition problem.

Be prepared/ equipped to check the spark if/when it happens again..

If spark Ok I think I'd next look at fuel flow and/or consider a stuck float but Id expect it to die more slowly ????
 
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Odd thing was it started fine when I got it back home... which leads me to think of some overheat problem.

I'll pop the plug out and take a look at it today.
 
Its one of those issues that you may only remidy once it breahs down again. Agree its probably linked with hot running but could be a coil breaking down or a fuel issue. I would suggest running it under load and try to get it to break down again. Then investigate the issue starting with ignition
 
steve66 said:
Its one of those issues that you may only remidy once it breahs down again. Agree its probably linked with hot running but could be a coil breaking down or a fuel issue. I would suggest running it under load and try to get it to break down again. Then investigate the issue starting with ignition
Click to expand...

Yes, I'll try it again in a deeper tank so I can open the throttle in gear more. The temps have dropped 10 degrees today, so it will probably be fine now!

I wondered if having the fuel in a tank that is so close to the engine and has the sun beating down on the top could make the fuel get too hot. Modern petrol has a much lower boiling point than ethanol free stuff we used to have.
 
Well I ran it again in the tank, under load at about 1/3 throttle and no problems. The tank water warmed up to about 40 degrees so it would actually be warmer than river water.

Here's the plug, looks ok to me?

plug.jpg
plug2.jpg
 
Geoff Theed said:
Probably stating the obvious, but could the air vent on the tank be closed or blocked?
Click to expand...

Ha! That old trick!

Well it was the first thing I checked....

The only thing that may be relevant is that I happened to throttle back and the motor died at that point and then failed to start. (Checked I wasn't in gear!)

I think when your engine fails you do tend to panic a bit, worrying more about how to get back. But I'm sure I checked everything, including leaving it for 10 mins. Normally it starts on even the gentlest pull.
 
RichardtheBoffin said:
Ha! That old trick!

Well it was the first thing I checked....

The only thing that may be relevant is that I happened to throttle back and the motor died at that point and then failed to start. (Checked I wasn't in gear!)

I think when your engine fails you do tend to panic a bit, worrying more about how to get back. But I'm sure I checked everything, including leaving it for 10 mins. Normally it starts on even the gentlest pull.
Click to expand...

I had an old 2 stroke that did that ... almost without fail. The only way to get it started again was to clean or swap the plug.
 
It could well be a problem with the coil as has been suggested already. I have a 4 stroke lawnmower which would run fine for 30 mins and then would cut out. If it was left for about 15mins to cool down it would start straight way and run for another 30 mins! It was always worse when it was hot weather or working hard. It proved to be the coil.
 
I wouldn't have thought it was a heat related problem. Although not a Yamaha but a Suzuki, the little four stroke I had for a couple of years in Greece behaved well despite the consistent high temperatures out here: no fuel issues at all. Got rid of it in the end because my wife couldn't start the thing reliably: a twenty metres swim followed by a 2 mile hike to sort the engine out was the last straw.

Edit: could it be the cut of switch? I know it's obvious and you probably checked it but perhaps an intermittent fault in the switch could be to blame?
 
duncan99210 said:
Edit: could it be the cut of switch? I know it's obvious and you probably checked it but perhaps an intermittent fault in the switch could be to blame?
Click to expand...

I'm sure it was a Yam 2.5 that we had once on a charter boat dinghy that cut-out and I couldn't restart it. I discovered that the clip on the cut-off switch had worn or something and was not holding the switch open enough. I wrapped some string arround it to hold it further open and it was OK for the rest of the holiday.

Richard
 
Sudden cutout like that could be failed head gasket. Look carefully at the plug to see if there are any traces of water on it
 
My Tohatsu 3.5 developed an intermittent fault that started running rough and finally cut out. I turned out to be corrosion on the earthing wire for the coil. Cleaning the contact cured it in about 10 minutes, but I stripped the carb twice before I noticed a ticking sound that turned out to be the coil sparking to earth.

Still, if the fault's gone with the heat wave, my money would be on fuel vaporisation. Worth checking you've got plenty of water coming out of the telltale, Poor flow means the engine will run hotter than it needs to , making the problem possible/worse
 
Just wondering if there is an over temp sensor and a problem with the thermostat? (no thermal cutout obvious in the manual, unless its inside the TCI unit?)

Sod's law says the moment I go near the river it will pack up again....

Next time I will just go 100 yards back and forth until the tank runs dry, so I don't have as far to walk to get back to the car!
 
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Are you talking about the modern F2.5A series? If so... I had the same issue with ours (which we have had from new)... then this thread sorted it out.

http://www.ybw.com/forums/showthread.php?342752-yamaha-2-5-carb-problems

Particularly the advice on post #3 from 'rusty barge'. This cured the problem.

I also gave it the Italian tune up... ran it a full revs in a tank with no load (so it could really get the revs up) for as long as I dared before the neighbours curtains began to twitch. This seemed to improve it's performance no end.

I think our problem was too little use, too infrequently and at revs that were too low. It was all gummed up with dirty fuel and water.
 
I would put a new spark plug in. The cooling could be a problem if it has been used in saltwater and little 'cleaning' in freshwater as the channels get blocked with salt/sand and require a strip down to clean out. That's my experience with a Malta ............
 
Little bit of an update.

Pulled the thermostat today.

As you can see the motor is mint,

yam1.jpg

but there was quite a bit of debris in and around the thermostat,

yam2.jpg
yam4.jpg

including another poxy impeller blade!

yam3.jpg


The guy who sold me this, really did it no favors running it up dry.....

The thermostat works perfectly at 50 degrees C.

While its unlikely the debris could hold the thermostat shut, it certainly wouldn't have helped the cooling.

So I cleaned out what I could and will give her another test on the river tomorrow.
 
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