What's wrong with my outboard?

machurley22

machurley22

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What\'s wrong with my outboard?

My venerable (15yo?) Yamaha 8hp 2T twin is auxiliary power for my even more venerable Hurley 22 which is about 2 tonnes in cruising trim.

The engine has recently developed a pronounced intermittent vibration. The last couple of times it has started after half an hour or so and then stopped again after a similar period.

The start of the vibration has also been accompanied by an increase in revs though I suppose this could be the effect of the vibration on the throttle linkage. I've checked for rubbish around the prop each time but found nought.

It always starts and runs (apart from this) reliably.
 
Re: What\'s wrong with my outboard?

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That sounds like fuel starvation - clean the carb, and maybe check the fuel pump.

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I hadn't considered that but wouldn't fuel problems cause a significant drop in power?
 
Re: What\'s wrong with my outboard?

Before getting too involved with engine. I would double check the prop.

Is it the type with a shock absorber bush in the hub?

Or is it just mounted on a shaft with a sheer pin?

If bushed the problem could be that area is starting to wear which would give intermittant vibes. If "pinned" could be the shaft or prop centre has wear , again would give the sympton. Just a thought, worth eliminating before attacking the motor.
 
Re: What\'s wrong with my outboard?

I hadn't considered that but wouldn't fuel problems cause a significant drop in power?

[/ QUOTE ]

On older two strokes if you shut off the fuel on the final gasps of the engine the engine races.
 
Re: What\'s wrong with my outboard?

Most two strokes will "race" as the float level drops when the fuel is running out as it affects the mixture(fuel air mix)

I query the fuel prob theory initially because of your observation that the engine will run ok for 1/2 hour then run ok later. Another thought comes to mind, is the posibility of a crank seal starting to fail.

However do the "prop check" 1st before we get too deep!
 
Re: What\'s wrong with my outboard?

Don,t advise chucking more oil at it. If you increase the oil/petrol ratio in a two stroke the desired effect is not always what you think.

I have come across instances where two much oil has actually had an unhealthy result. As you alter the ratio you also alter the fuel air mix, ie the mix becomes"leaner" could lead to seizures sounds daft I know (more oil leads to seizure?) but I,ve experienced the phenonomen.

Understand where you,r coming from but it,s not quite the same "remedy" as a four stroke.
 
Re: What\'s wrong with my outboard?

[ QUOTE ]
Before getting too involved with engine. I would double check the prop.

Is it the type with a shock absorber bush in the hub?

Or is it just mounted on a shaft with a sheer pin?

If bushed the problem could be that area is starting to wear which would give intermittant vibes. If "pinned" could be the shaft or prop centre has wear , again would give the sympton. Just a thought, worth eliminating before attacking the motor.

[/ QUOTE ]
That makes sense to me Kwacker. The engine itself (as opposed to transmission) seems to run fine whether the engine (as a whole) is vibrating or not. I'm not sure whether I've got a rubber bush since the book is aboard but I'll definitely check the prop next weekend.

Dodgy crankcase seals usually cause starting problems IIRC.

I wonder why Kawasaki never made outboards like the other three?
 
Re: What\'s wrong with my outboard?

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IMHO its f#rked, get a new one.

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Ahh - an expert at last.

Thanks for your contribution, I will give it my most earnest consideration.

When are you coming to crew on Silkie?
 
Re: What\'s wrong with my outboard?

I agree with the theories about fuel starvation causing an inrease in revs but I have not noticed any vibration accompany this. Have you tried pumping the fuel bulb to see if that stops it? If it does you will have to look at the fuel pick up for small air leaks, the fuel pump and the filter. Does operating the choke have any effect. If it is fuel starvation in any sense that should stop the problem.

Without wishing to reignite any arguments about old fuel you are using clean fresh fuel aren't you? and there is no muck in the tank is there?

Have you considered an ignition problem. I'm sure it wont cause an increase in revs but a dodgy plug or lead may cause the vibration. It can also be the sort of thing that is intermittent. I assume an engine as young as 15years will have an electronic ignition system so points and all that stuff won't come into it but it might just be worth pulling the plug leads one at a time (but beware of getting a bit of a belt!) If removing one of them has no effect then that points to an ignition fault on that cylinder. Swapping the plugs and repeating will determine if it is a dodgy plug.

If the plugs have seen 15 yrs service it will be worth changing them any way (you carry a spare set don't you?)

If the suspicion that it is fuel related persists then it could be that it is time to clean the carb. Properly, not just spraying some carb cleaner in. It could be some muck in one of the jets but that is unlikely to cause an intermittent problem. You do always run the carb dry at the end of every weekend, or whatever, don't you?

The final thought is the opposite of fuel starvation. Some two strokes tend to four stroke when running rich. Seagulls do it and so do my mowers but I have no experience of it on a more sophisticated or two cylinder engine. It'll increase the vibration considerably but I would not have thought you would see it as an increase in revs. Opening the throttle a bit, so that is working harder, usually stops it, initially anyway. If that is a possibility then you need to look at the the mixture setting, the fuel level in the carb and the posibility that the needle valve is not seating properly so allowing the carb to flood slightly.

Do the easy checks first and work towards the more difficult. Leave dismantling the carb 'til last and do it very carefully to avoid losing any little bits.
 
Re: What\'s wrong with my outboard?

Had the same problem a few weeks ago, cleaned the jets and all is ok now.
my engine is same model but couple of years older.
 
Re: What\'s wrong with my outboard?

Listen bud I,ve got enough on me plate without manufacturing outboards! /forums/images/graemlins/smirk.gif

"Kawasaki Heavy Industries " is the "Parent" Co, making all sorts of things Shipping "Heavy" engineering bloody huge conglomeret outboards in there perhaps ,never really checked, maybe in" another" name. Will check just for interest. Yer got me thinking now! Although "Kawasaki" meens Motorbikes to us plus a bloke who drivels on the Forum /forums/images/graemlins/tongue.gifit,s like Mitsubishi Who make cars and the odd tele or two got to hand it to the Slant Eyes now and again! /forums/images/graemlins/wink.gif
 
Re: What\'s wrong with my outboard?

Thanks for the detailed reply Vic though I obviously didn't explain myself very well in the original post.

I'm fairly sure that the small increase in revs is incidental (the vibration overcoming some stiction in the throttle linkage) since the engine continues to run as normal. The engine note is unchanged and there is no indication of it four-stroking or otherwise misfiring.

I really think that the cause is a mechanical imbalance and K's suggestion seems the most likely so far.
 
So that\'s what was wrong with my outboard!

[ QUOTE ]
Before getting too involved with engine. I would double check the prop.

Is it the type with a shock absorber bush in the hub?

Or is it just mounted on a shaft with a sheer pin?

If bushed the problem could be that area is starting to wear which would give intermittant vibes. If "pinned" could be the shaft or prop centre has wear , again would give the sympton. Just a thought, worth eliminating before attacking the motor.

[/ QUOTE ]
It's always nice when someone comes back to report on the resolution of their problem even if it is 13 months later, so . . .

The vibration problem got much better after my initial post; less frequent and less severe so being essentially a lazy sod at heart I ignored it until last Thursday. Motoring W to E through Cuan Sound, I was about 50m off Cleit Rock when the engine revs suddenly increased and I lost all thrust. Fortunately it was neaps and just the start of the ebb so I had time to make sail and regain steerage before the crunch. I sailed up to Balvicar Bay and on to my mooring (OK it was the next door mooring but still not too bad for an amateur) and found this after removing the prop.

DSC_0081.jpg


So thank you Kawasaki, you were spot on - even although I didn't do as you suggested. Almost incredibly, the amazing Stoddart's in Oban (no connection etc) had the identical prop in stock and we were ship-shape again by the following afternoon.
 
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