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Old 13 July 2003, 09:47   #1
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Help Engine Problems!

Can anyone help....?

Had my rib out last week for the first time..... and had a problem with the engine.

It ran fine for approx 20mins, then suddenly decided to drop power to approx 2/3rds! After this point I was never able to achieve full throttle again!

I checked the throttle cable etc to ensure that it was moving the throttle on the engine the correct distance and all is fine.

Before I switched the engine off, the water spray from the engine to the sea stopped working aswell!

When the initial problem with the 2/3rds power started the water cooling was still working, the second problem only appeared as I was returning to the marina.

Do these problems point to a dodgy impailer (spelling?)... and would that cause both problems that I am seeing?

Sorry for the vague question, im not very clued up on outboard engines and the terminology to use!

Cheers for any help given......
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Old 13 July 2003, 17:24   #2
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more info

Gadge can u describe the rev problem a bit more, was the boat going in the same direction or returning on its initial course ( were you driving against tide is it possible you were experiencing cavitation just athought, the cooling problem might not be a problem is it possible the thermostat had shut for a moment, my old Mercury would do this and when it needed the stat would open and cooling would continue again, what is the make of the motor is it 4 or 2 stroke etc
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Old 13 July 2003, 17:48   #3
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Gadge, It sounds as though your engine may be over heating. Most modern motors will force the revs to be limited if this happens. Check the impeller. If it is broken up, you need to find the pieces because they will block, or maybe have blocked, the waterways. There could be other causes but this is the first thing to investigate.
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Old 14 July 2003, 05:28   #4
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Gavin - think carefully before you answer - what differance does it make which way the tide is going?

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Old 14 July 2003, 18:24   #5
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direction

It shouldnt make any difference , I am wondering as I dont know the size of the motor ,if running with the tide it will accelerate quite easiely with wind behind you, but if you turn about, your motor will seem like it is working harder to get you there if you are driving into the weather for example, what do you think is the problem with the revs?
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Old 15 July 2003, 02:21   #6
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Gavin - I would hesitate to say for sure, but if it was cavitating the engine revs would pick up and the speed would drop. Unless this information was left out by Gadge.

The newer engines all have a get you home mode if there is the slightest problem - for instance if it is low on oil or the cooling is not working properly. It could be a poorly sensor - I could go on all day with the information given.

I am not a Mercury engineer, and knowing the trouble some of them have in sorting out problems like this I would not even want to start on a diagnosis!

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Old 15 July 2003, 08:51   #7
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The engine is a 1997 50hp Mercury..... its a 2 stroke, 3 cylinder.

I believe the overheating problem could be an accurate analysis.

When it initially happened and the power dropped to approx 2//3rds the engine revs also dropped at the same time. Every time I have had the engine running up until now, the water cooling has been working constantly.

I have previously been told that normally the water cooling wont start until the thermostat opens and the engine has heated up. However whenever my engine is switched on the water cooling is always working.

On my return trip, the water cooling didnt work once! As mentioned does this point more and more to an impeller problem?

Im going to have a look at it tonight, where is the imepller situated on these engines?

PS... Cheers for the help so far folks, sorry for the vague descriptions!
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Old 15 July 2003, 09:05   #8
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Could also be an oil of fuel problem? If their is a lack of oil getting in it may reduce revs the hpdi's come down to 1600 rpm when their is an oil fault or no oil. This is to reduce or prevent damage. The optimax run on a pressurised oil system. If air gets into the system the engine will only run at low revs (i have forgotten how many) Check the manual to see if it should be pressurised. I doubt it for a small engine.

Fuel starvation would probe cause the engine to stall unless it was the chip in the fuel pump that was miss behaving. In this case it might reduce its revs.


don't know this engine though and it does sound like it could be cooling related if this happened at the same time.
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Old 15 July 2003, 10:14   #9
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Gadge

I had a simular problem at the weekend, when going full throttle the revs dipped and the engine eventually died on me, i could then restart the engine ok and it was fine for a few minutes, back on the beach my trusty mechanic pulled the thermostat out of the head and ran the boat engine on clean water, the power head got hotter and hotter.
Currently its at the workshop being looked at and they think its either the water pump or the impellor thats nakered, apparently on mine there's a thing that switches the engine of if it overheats and drops it down to very low revs.

Not sure if all this helps but it sounds like your on the right track, i've been told that the impellors are so fragile even running for a few seconds without water going through will damage them, if a stick or stone goes through the intake its likely to damage the impellor, or like mine it may just be a symptom of an older engine.

Richard
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Old 15 July 2003, 10:20   #10
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Impellar location

Gadge
Sorry forgot to mention on my boat the impellor is located in the lower leg, this means the gear linkage need to be undone and the lower leg dropped off to get to the impellor, not a job i'd do myself, others would disagree but i'm not a mechanic. Think this is where most impellors are located on outboards.
Good luck if you have a go yourself.

Richard
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