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Yamaha outboard 25hp suddenly wont go into high revs. Fuel issue?


lucyboatgirl

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Hi everyone,

I am at a total loss with my Yamaha outboard 25Hp engine.

 

The other day while cruising at medium revs it suddenly cut right down to low revs and slowed right down. Even when I gunned the throttle it still just stayed in low revs.

I moored up and had a look at the prop and pulled some weeds out but nothing serious and then tried her again. The engine started fine and goes low revs fine but wont go anymore than that no matter how much throttle I give it.

 

Any suggestions about what this could be? I have been advised that it might be a fuel line problem or fuel flow problem.

Any suggestions where to start? The fuel line I bought new last summer so I doubt it is that. If anyone has any advice that might help I would really appreciate it. Or can point me towards any youtube videos that I might be able to follow to fix it.

 

Thanks for all or any help you can offer. It is very very appreciated and I hope you all having a beautiful and un-broken down day out there on the water.

 

thank you

xxxxxxxxxxxxxx

 

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Blocked jet - I had that problem on a Seagull years ago. It also suffered from gloopy fuel, so I started adding 'snake oil'  to the fuel which helped.

There aren't many folks on here with outboards, so you may not get many responses.

 

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Maybe the tick-over jet is clear, but the main jet (that comes into play at high throttle levels) is blocked ?

Is it a 2-stroke engine ?

Do you always run it dry before stopping ?

 

If it is 2-stroke then the petrol evaporates in the carb leaving a gummy-oil residue that blocks the jets.

 

I have just had to clear my Son's OB for exactly that reason.

 

In future : Turn off the petrol before stopping the engine, keep it running until it either starts to 'race' or starts to 'hunt', then turn off the ignition and the carb will be dry and won't get gummed up.

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20 minutes ago, lucyboatgirl said:

Hi everyone,

I am at a total loss with my Yamaha outboard 25Hp engine.

 

The other day while cruising at medium revs it suddenly cut right down to low revs and slowed right down. Even when I gunned the throttle it still just stayed in low revs.

I moored up and had a look at the prop and pulled some weeds out but nothing serious and then tried her again. The engine started fine and goes low revs fine but wont go anymore than that no matter how much throttle I give it.

 

Any suggestions about what this could be? I have been advised that it might be a fuel line problem or fuel flow problem.

Any suggestions where to start? The fuel line I bought new last summer so I doubt it is that. If anyone has any advice that might help I would really appreciate it. Or can point me towards any youtube videos that I might be able to follow to fix it.

 

Thanks for all or any help you can offer. It is very very appreciated and I hope you all having a beautiful and un-broken down day out there on the water.

 

thank you

xxxxxxxxxxxxxx

 

Could be Water in the Fuel?drain the Carburetor and check for Contamination.just a couple of drops can cause Erratic Running.

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Thanks for your help guys, but I don't actually know what a jet is? Ha ha. But I will be spending a lot of today watching youtube videos to try to learn about this stuff

What do you reckon though? If its a blocked jet do you think it is something you can teach yourself to fix or am I best calling a mechanic?

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Hey alan its a 2-stroke, and saying as I had never heard of running it dry before stopping this is obviously something I have never done. ha ha! Good advice though. But I don't understand how you would 'turn off the petrol' before the engine?

 

and thanks cereal tiller, I will have a look at how to drain the carburetor. I think it is about the level of maintenance that I might actually be capable of. ha ha

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Also have a look at what moves on the engine when you open and close the throttle.  Typically outboards have a mechanical link that advances the ignition as you open the throttle. They tend to rotate the stator that sits below the flywheel. If this mechanism fails they will not rev up. However carburettor jets or water would be my first thought.

4 minutes ago, lucyboatgirl said:

Hey alan its a 2-stroke, and saying as I had never heard of running it dry before stopping this is obviously something I have never done. ha ha! Good advice though. But I don't understand how you would 'turn off the petrol' before the engine?

 

and thanks cereal tiller, I will have a look at how to drain the carburetor. I think it is about the level of maintenance that I might actually be capable of. ha ha

Take the fuel hose connector off the tank or off the engine, whichever is easier. You could try screwing the tank air vet screw down (light bulb moment - see below) but the engine may suck sir into the tank via an old filler cap seal.

 

I suppose you have unscrewed the air vent screw that is normally in the tank filler cap! If not that would cause fuel starvation and the engine might well run on idle but nor rev p.

Edited by Tony Brooks
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Hey Tony,

The air vent on the tank is open so its not that but thanks for the attempted problem solving!

 

So would the advice be when normally running my engine and turning it off that I disconnect the fuel line and let it run out of petrol rather than switching the engine off? Have I got that right? 

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My little 2hp 4 stroke had a blocked jet one year when i forgot to drain the fuel over winter, fairly easily cured if you can find instructions. 

 

I always turn the fuel off until it runs dry (when I remember) and drain down over Winter

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33 minutes ago, lucyboatgirl said:

If its a blocked jet do you think it is something you can teach yourself to fix or am I best calling a mechanic?

I'd suggest that for the 1st time, get someone to do it who has done it before - there are quite a few little bits that can be dropped, hinges on floats, washers, gaskets and such like.

Once you have seen it done its quite a simple operation and well within normal 'DIY' skill requirements.

 

Ideally remove the carburettor (normally just 2 bolts), disconnect fuel hose, disconnect throttle and choke cables and remove from the engine.

Hold it in a 'tub' as petrol will leak out when you tip it upside down to remove the bowl (float chamber).

Remove float (watch for fuel shut off pin falling out and getting lost)

You will find the main jet  'inside' the top of the 'bowl' screwed into the body of the carb. Make sure you have a correctly sized screwdriver and remove the jet (lefty loosy, righty tighty)

 

Once removed you will see holes in the end of the jet (running lengthwise and probably crosswise at the tip of the jet)

 

DO NOT POKE WIRE, PINS OR ANYTHING ELSE INTO THE HOLES - YOU WILL DAMAGE AND PROBABLY ENLARGE THEM.

 

Blow down the holes and try and clear them, if you cannot, then try a single bristle from a hairbrush or toothbrush and gently poke it thru.

 

If it will still not clear, go back outside, (off the boat) pour some petrol into a tub and put the jet in to soak for an hour or so, dry off and try blowing thru it again,

still blocked ? Use the hairbrush bristle again,

still blocked ? call for help.

 

It will normally clear quite easily just by soaking and blowing.

 

Good luck and don't be 'frit' to try it. (download the manuals, take it slowly and work on a table with a cloth on it to catch the bits that drop out) 

 

 

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Judging by your questions and the response to the answers and suggestions, I would say that your safest bet is to find someone who knows what they are doing, ask for their help and watch carefully, asking questions as you go.

I have done this in the past with plumbers, mechanics, electricians, brickies, decorators etc. They all seemed pleased that I wanted to learn and were happy to teach me.

If you do it yourself use your mobile phone to take pictures of everything you do, as you do it. This helps enormously when you come to put it back together and you can't quite remember where that little spring came from and where it should go back!

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On 02/07/2018 at 11:55, Mike Hurley said:

I might be stating the obvious but have you checked the throttle cable has not snapped/come off?

Exactly what I was going to suggest. That happened to me last year.

The cable had sheared off at where it's bolted to the outboard engine and turns a bit that tells the engine when to go from forward/neutral to reverse.

It's easy enough to remove the cable and install a new one.

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Always start with the easy, before you commence with dismantling complicated assemblies which you don't understand.

 

As has been said above, check that the cable is actually connected to something at the outboard end.

Remove the Spark Plug(s) and compare, are they grey or black and are they both the same colour?

 

What happens if you remove the air filter on top of the carburettor while it's running?

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Hey you lot,

some super brilliant advice here so thanks very much.

Alan de enfield thanks so much for taking the time to write that for that really careful and detailed guide. I will totally be using that when I try to clean up my little engine which I am sure it needs.

 

And super thanks to mike hurley for stating the obvious because obviously I need it stated. ha ha! Yes it is a snapped throttle cable!!! I didnt actually know this was a thing. It has just snapped in two so mystery solved. Sorry to have bothered you all with this mystery problem when a simple look around my engine would have totally confirmed what it was. Someone just said to me that it was probably a fuel issue and I totally believed it without investigating myself! ha ha! So stupid to make assumptions like that. But at least I have got some really good advice on how to clean and care for my engine and how to clean the carburettor.

 

So I am now about to watch any videos on youtube I can find to learn how to replace this myself. Any advice you might be able to give on this would be amazing! But even better would be a recommendation of where I could order a new cable, hopefully somewhere that would be sympathetic to someone who doesn't really know what they are doing but eager to learn and do it themselves. 

 

Thanks for all your help as usual you wonderful boaters. So helpful it's not true!!!!! You guys rock the fuckin ocean x

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4 minutes ago, lucyboatgirl said:

Alan de enfield thanks so much for taking the time to write that for that really careful and detailed guide

Not bad for a creepy stalker eh! :)

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5 minutes ago, lucyboatgirl said:

Yes it is a snapped throttle cable!!!

This is the video you need. This is what I watched before I replaced mine.

 

TIP: when you replace the cable, do NOT try and force the stick into reverse (to test things) when the engine is off. That's what I was doing. Like a right numpty.  :blush:

 

 

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