Yamaha 25hp

[macca172]

All,

Picked up a tinnie fitted with a Yamaha 25HP a couple of weeks ago and took it for its maiden voyage yesterday. Ended up having a problem, however firstly by the look of the plate on the engine, I "thinK" the model number is a 61_2? The guy who sold it to me, said it was only a few years old with less than 50 hours use. Its looks in tip top condition and is clean as a whistle.

Anyways the problem:

Left Berowra Waters ramp, motored down the channel at 4 knots which took about 10 or so minutes:

Once clearing the 4 Knot zone, opened the throttle and it took off without missing a beat. Throttle was about 1/4. doing about 20 knots+. Engine was very responsive.

After about 4-5mins the engine "suddenly" without warning came back to idle speed. No splutter splutter, nothing just cut back like I had set the throttle to idle.

Checked all the obvious, fuel flow ok, water pump tell-tail good and strong flow and fuel tank ventilation ok!

At idle speed we motored to a beach and had a look at the engine(still at operating temprature), nothing obvious.

Sat down had a smoke and after 10 mins fired engine up and off we went again, went all ok for another 5 mins then the same again, back to idle speed only, with throttle wide open? Let engine cool for 10 mins and once again fired it up and off we went for 5 mins and about 20 knots and then it died back to idle again. To get some knots out of it, so we could get back to the ramp, I held throttle wide open, although it was only giving just above idle revs and we motored back at about 4 knots(long bloody way I tell you). After about 10 mins, without warning with throttle still at max setting, away it roared without warning and then once again, 5 mins later, same old story, idle only.

My question is, is it at all possible this model motor is fitted with a high water temp cut out/safety switch that could be possible faulty ie: shorting out etc? I dont believe from my observations that the water pump is faulty, as the there is a good water flow showing. Im not a guru on outboards of the size so any advice would be greatly appreciated.

Macca

Edited February 17, 2007 by macca172

[ETTY]

Not being an expert either!

Some people I've heard have had similar problems (like you suggested) with themostats being faulty which only allows the engine to run at idle to prevent engine being damaged due to overheating - which makes sense when you stop the engine cools then works fine but when it heats up when you've gotton going it malfunctions and runs at idle.

I think your on the money with that one but take it back to the dealer/mechanic and he'll be able to diagnose the problem.

Good Luck

Elliot

[macca172]

Etty,

Thank for your response and yes I tend to agree somewhat. However, did some further research today on the donk and came up with the following;

Its a 1993 model 25N 6L_2( its in great nick for its age)

This model is not fitted with an overheat safety device( had a look and definitely not fitted); and

Rang a guy in the boat trade this morning and he said it sounds like its one of the two fitted CDI's breaking down?

So tomorrow morning Im taking to my local Yamaha outboard dealer for a look see.

Macca

Edited February 18, 2007 by macca172

[macca172]

Had a call from the outboard service guy today. He said the only problem they could find was that the bottom carby was full of gunk? He said they will overhaul both the carbies and it "should be" a go'er again. Also he said the compression in the pots were down a bit, however he stated it was most likey caused by the motor being not used in some time. He said the fix was to put some chemical in the pots and let the rings loosen up again. Any ideas what chemical could be?

Macca

Edited February 26, 2007 by macca172

[Flightmanager]

G'day Macca ,

" Gunk " in the carbs , and on the rings indicates that the motor has been left to sit for quite a while with no use. The petrol component evaporates , leaving behind a gum , which if not removed can lead to poor running , and even failure of vital components like rings etc.

I would think the chemical would be a degreaser or solvent of some description.

Ross

[macca172]

Ross,

Thanks for your response. Do you think that the "gunk" as I described it, is the main cause of the problem as I outlined in my initial post? If one carby was to stop working, would the engine cut back to idle rpm and after ten minutes of cooling down so to speak, run normal again?

Macca

[Flightmanager]

G'day Macca ,

A gummed up fuel system could possibly cause unusual running , but it is also possible that one or both of the CDI's could be causing the problem . Having the carbs overhauled is a good place to start , once done if it doesnt fix the problem , then the next obvious choice would be electrical.

Sorry I cant be more specific than that , it would have been good if you could jave pulled the plugs on the day to see if they were wet ( unburnt fuel ) , or tested them for spark ( strong , weak , none ) .

Kepp us advised of developements .

Ross

[macca172]

Guys,

Picked it up from the Yamaha service guy today....ouch $390.00! The upshot is both the carbies pulled down, cleaned out and serviced. Also sold me a 200ml bottle of chemical(engine de carboniser) which I add at 10ml per 10 litres of juice. Techo told me they had tank tested it and is running all ok now. I will take it down to Berowa late next week for a run....will advise.

Thanks for all your input and advice.

Regards,

Macca

[johnno]

Good to see it's sorted

now you can focus all your effort on fishin

[macca172]

Guys,

Good news, took the boat down to Berowra again yesterday, fishing was lousy but the Yammy went like a dream.

Valuable lesson for people who store outboat motors for long periods, make sure you drain "all" fuel from the engine before storage.

I emailed the guy who sold me the boat and told him I had problems and asked him how long it was in storage for( he told me when I bought it a week prior to it breaking down "oh it was used regulary")it was in fact in storage for 14 months! Oh yes he also said in his reply also "sorry to hear your having problems"! Yeah $390.00 worth of problems!

Oh well valuable lesson for me as well, never trust a work ex collegue!

Once again, thank you all for your valuable advice and assistance!

Macca

[Flightmanager]

Great news mate !! I frequent an outboard motor forum , and this is a very common problem , particularly in the states where it is too cold to use the boat during the winter months. As part of the preparations for the summer months , they religiously re-do the carbs , to prevent the problems that you had. Luckily , over here it is not such a large problem UNLESS the boat has been sitting for a long time !!

Ross