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Old 14 April 2019, 05:23   #1
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Country: UK - Scotland
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Yamaha 115 outboard

Hi All ,
I am a member of a scuba club in Scotland our boat is predominantly used for diving activities. We are having a problem with our engine which seems to have stumped the yam dealers so i wondered if anyone could help as we are at the end of our rope with this so here goes . We have a yamaha 115 4 stroke outboard on our typhoon rhib engine is 6 years old .The problem is at tick over after about a minute or two the tick over speed starts to drop from 8hundred rpm slowly 7,6,5 then cuts out .We have had the engine serviced all filters etc changed engine shows no faults this work is all carried out by official yam dealership . Problem persisted dealer suggested changing an air flow sensor price £260. No improvement . I was doing the i will have a look thing and discovered if i lifted the engine cover the tick over speed came back to normal .We have been using the boat with the engine lid lifted slightly at the front even a small gap of 10mm is enough to run normally. I assumed it was an air flow problem so i removed the front cover and the top internal cover from the engine lid to check if any obstructions .There were none i fitted the engine lid without the covers and locked the catches .The problem reoccoured so back to square one . I also checked if anything was being crushed etc but cant see anything .Suggestions from dealer change the engine bugger that ,start changing components with the hope of a process of elimination = sound expensive with a small chance of improvement ,live with it .If anyone has come across this problem or any sensible suggestions would be greatly appriciated .
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Old 14 April 2019, 06:53   #2
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Does the engine fade away id you lift the idle rev lever beside the throttle , even if you move it a tiny bit?? The idle revs can be changed on the yam instrument engine clock we have...can you do this?? It changed the trolling speed. With the boat on a trailer,with the cover off , does it cut out? Keep us posted , we'll find the answer!! Nik
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Old 14 April 2019, 09:39   #3
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Yamaha 115 outboard

This probably doesn’t help but......we had a very old yam 2 stroke once with the same problem and eventually traced it to loose insulation inside the engine cover which was being drawn onto the air intake.
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Old 14 April 2019, 09:40   #4
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I have a similar problem with a 25 Suzuki mine will start run at high revs but tick over it dies but if I pump the bulb it come s back if it stalls the only way to get it going is to pump the bulb put in gear and keep pumping the bulb until it gets to about 2-3000 rpm it will then run all day. it's in the shop again Suzuki technical recons fuel blockage it's done 120 hours they have changed the filters but not the high pressure filter which should be done at 1000 hours like you at the end of the tether so I've instructed them to change the inline mesh filter and the low pressure filter plus the high pressure filter which is after the high pressure pump if that fails it goes back to Suzuki for them to sort still under warranty though.

Maybe no help but worth putting it in the mix
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Old 14 April 2019, 10:04   #5
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Yeh, thats a point....can you keep the engine idling if you squeeze the fuel bulb??
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Old 14 April 2019, 11:09   #6
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yes it does the same if on the trailer running in the tub .The dealers agreed with me after i pointed out what was happening .They had obviously been working on the engine with the cover off .As soon as they tried it with the cover on the problem presented. I havent tried pumping the fuel bulb will try it to see what happens .The rev lever on the console control will keep it running if its set to a higher speed but on our boat if the lever is not down in the parked position we cannot put it out of neutral ? i dont know if this is normal or not as its always been like that .Thanks for the replies .
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Old 14 April 2019, 11:24   #7
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Yeh ,its normal re the idle lever....it locks out the clutch and hence you cannot put it in gear with the engine in fast idle.
If when the engine is idling for say 5 mins in the tub/or muffs you put the engine cover on does the engine start to stumble and eventually die??? Just checking I've got that right?
On your yam clock you can increase your idle so you can maybe use that to keep things going until we get this solved.
i'd be dead interested if squeezing the fuel bulb keeps the engine going??
Do you think it sounds as if the engine is been smothered with the cowl on? Pinching some fuel line or obstructing an air passage??
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Old 14 April 2019, 13:05   #8
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Country: UK - Scotland
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Yes. doesnt matter where the engine is in sea or tub as for adjusting the idle when the engine is running ok the idle is around 800rpm havent tried adjusting the idle where is the clock ? is this on the engine or console i will try the fuel bulb next time out .I had a look at the throttle stop on the engine and see there is a stop screw its an anti tamper pin type torx head so probably dont want you to mess with it ? As the engine runs fine with the small gap left in the lid we are reluctant to start messing with it .It is also a club boat so a lot of politics goes with it .We have a few members who think dont touch and leave it to the professionals .I see there point but we have spent about £700 now admittedly this covers service items as well but when the professionals dont seem any the wiser .
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Old 14 April 2019, 13:16   #9
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In my book is a list for engine tends to stall
Neutral switch failure
Throttle position sensor fail
Iac control system fail
Iac passage clogged
Ecm fail
Wire continuity, connection fail
Fuel injectors clogged
High pressure pump fail
Fuel filters clogged
Clogging bent In proper routing of fuel hose

Not an expert by no means but isn't the cowling designed for the correct intake of air so if fuel was starved would this have an effect at tick over, just a thought with the way it acts with the cowl open a bit
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Old 27 April 2019, 00:47   #10
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Have you considered contacting Yamaha UK directly the number is 01932 358000 give it a shot and ask for tech support
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