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Engine Trouble- revs going down intermittently


Mutt

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Hi,

I have a 2003 Yamaha 2 stroke 60 hp engine that has rarely given any problems- until today! 
It is regularly serviced but has been over 2 years- will get it serviced soon.

Hopefully a service will fix it but want to see if it sounds a bit more sinister than a service!!!

Last 2 outings when at 3/4 speed the engine just lost all its revs and I couldn’t increase speed- was like the prop had stopped. Checked the prop and all ok- started again and it went fine for the rest of the trip.

Same thing happened today a few times but coming back to the ramp the engine lost all revs and cut off a few times.

Always restarted but today couldn’t get the revs up again at all.

Managed to limp back to the ramp and when flushing the engine it cut out a few times as well.

Starts no problem and plenty of fuel and oil.

Just putting out there if anyone has any ideas what it might be so I can make sure it is looked at when I get it serviced?

Thanks in advance!

Mutt

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Nothing definitive to offer, but just the basics to look at (which you may already know):

Start with new plugs.  May not fix anything, but won't do any harm.

If you have a separate spare tank with a separate fuel hose, hook that up to rule out any restrictions in the fuel system.

Check that the fuel pump is operating as it should be.

Check that your oil mixing system is working properly.

Check that the engine isn't overheating and near-seizing.  If it's peeing a steady stream, you can prolly disregard this one.

I think that these are CDI ignition.  If you can borrow another CDI unit to swap over, that would rule out the CDI.

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I recently had an issue with the fitting on the Yamaha tank , the little pin in the fitting which gets pushed in to open the little valve was sticking and when I re fitted the tank after re fueling I had problems with the engine losing power and stalling . It was starving the engine of fuel , I had a similar problem with the fitting on the engine as it wasn’t quite pushed home - all ths started when I replaced the genuine fuel hose as it was starting to split . I have heard of the valve ball inside the primer bulb causing similar issues . Best thing to do is take it to a Yamaha service centre and tell them the symptoms - they will tank test it and know what to look for .

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Before we go too far, a "service" is routine maintenance, not a repair! If you are taking it in for a service, make sure you mention it has an issue........now, you need to do some very basic trouble shooting, remove the plugs and have a look at them, do they all look the same? are they dry or wet? Can you check spark on all cylinders? the 3 cylinder Yamaha has quite a unique ignition system! Also the chances of a dead power pack/CDI module on a Yamaha is slim at best. Then try a complete other tank, complete with fuel line and fittings (borrow one if you have to) when it dies, does it just stop like turning the key off, or just "fizzle" out? A simple fuel pump test is to pump the primer bulb when it plays up, does your alarm work?

Edited by noelm
Typo
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Also on your tank is the air breather open ? If it is an under floor unit check the breather is clear . Maybe a crook connection between one of the coils and the Ignition module causing one cylinder to intermittently shut down ? Is it manual choke - ie pull the knob out on the motor or electric choke - ie push the ignition key in on the throttle control ? Possibly a dodgy switch causing the choke to activate while the engine is running ? Just a few thoughts !

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The fact that it's cutting out. Very much so sounds like a fuel issue. Have you got air pockets in the fuel lines? Maybe an injector could be blocked? 

Sorry can't help you more, mainly focus on diesel car engines.

Edited by slothparade
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Should be basically the same layout as my 2003 40hp 3cyl motor - just a bigger displacement engine . I’m led to believe the 40&50hp 3cyl engine are the same displacement  and was told the 40 runs a restrictor  plate between the carbies and the crankcase and the carbies may be jetted differently to compensate . Mutt mentioned in the original post that it had plenty of fuel and oil so I would take it as being oil injection .

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Seriously- you guys are all amazing!

Thank you so much for your suggestions and advice- really appreciated!

Will do what I can do following your suggestions and go from there- sounds like a fuel issue so will start from there….

Thanks again!

Mutt

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  • 2 weeks later...

I had a really similar issue with my yammie 50hp 2stroke. Ended up being a blow. Head gasket. Plugs were wet with water. So 2 of the 3 cylinders werent getting fired.

you cant burn water

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  • 6 months later...

Just an update and a bit of valued help/suggestions….

Have had a mobile marine mechanic look over and work on the engine twice now- lots of work done, new plugs, service, battery replacement etc etc.

Engine starts fine but took the boat out and it lost all power again- ran beautifully for about 20 minutes at max speed but then lost all power again- engine stays running but when I apply throttle - no power or revs.

Turn engine off, start again…engine runs fine for awhile and then it happens again- seems to happen when running at close to max - just drops revs and nothing happens when I apply throttle.

Limp back to ramp and scratch my head!

Mechanic wanted to try an on water test but this can be hard to organise etc and no guarantee it will lose power…

Anyhow- you guys are legends and know a lot more than I do about engines- any suggestions/thoughts as only want to do an on water check if really necessary???

2003 Yamaha 60hp 2 stroke

Thanks in advance!

Mutt

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On 4/21/2023 at 10:39 AM, rickmarlin62 said:

Try cleaning carbies  bits of gunk float around then block jet  when you stop or lower revs back to idle jet it falls away  off you go till it blocks again

Just saw this- thanks- I’m sure the marine mechanic mentioned cleaning carbies as an option… will ask if he did that when he worked on the engine.

Thanks!!! 

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Mutt, from your post earlier today, it reads as though your mechanic has carried out a service, but nothing to specifically address the engine's issue.

 

This is not to disrespect what your mech has done...a service will get the basics right which is a good starting point, but now he needs to try and understand what is going wrong after running for a while.

 

In any field, the key to solving a problem is to be able to re-create the problem on demand.  If you can, rig up a tank so that you can re-create the problem.  Run the motor, in gear, at x rpm for y minutes.  To do this you will need a large enough tank to be able to do this on your driveway.  I wouldn't run a motor at more than moderate revs with ear muffs,

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