Yamaha 40hp 2 Stroke Intermittent Fault.

MattB · 14 April 2016, 08:57

Our 5 metre rib Yam 40 engine has a very annoying intermittent fault. Out of nowhere it goes from running sweetly to cutting out/not reving/not starting. It is well serviced by a professional outboard mech. He has confirmed there is no issue as far as he can tell. Typically, when he sees it it's working fine. All he can recommend is a new CDI but does say in 40 years of working he's only replaced a couple.

The boat is used as rescue cover for sailing dinghies so does spend a lot of time on tickover. But is really only used a max of 5 hours a week. It is in a freshwater lake.

Anyone else any other ideas? I've tried numerous lines and tanks as I have access to a few. Does sound like fuel but we have kind of eliminated that.

Or do we have to try for the CDI? At around £1,000 to replace want to make sure everything else has been ruled out.

Many thanks.

matata · 14 April 2016, 09:30

Does the engine die away very suddenly say in two/three seconds or fade away over ten/fifteen? how do you get it started again? does it start miss firing before it stops? does squeezing the fuel bulb as its dying away regain it back to life. Do you have to sit and wait or keep churning the key? Is there any regularity to it i.e. rough seas or after a long day of use or after long flat out sessions etc I think if the engine cuts out again I'd have a spark plug spanner handy and before I tried to start it again I'd have a good look at the plugs. wet/dry etc Then i'd turn her over looking for a spark on each cylinder. I know its not the most pleasant thing to be doing at sea but its prob a great way to get to the bottom of it. On dry land with a cup of tea i'd do a compression check because its easy and rules out 60% of your problems.! Keep us posted Nik

Fenlander · 14 April 2016, 10:02

>>>I'd have a spark plug spanner handy and before I tried to start it again I'd have a good look at the plugs. wet/dry etc Then i'd turn her over looking for a spark on each cylinder. I know its not the most pleasant thing to be doing at sea but its prob a great way to get to the bottom of it.

Yep totally agree... back to the old fashioned basics of any engine with running issues... albeit as said above not quite as easy at sea but that's the crucial time to gain evidence.

willk · 14 April 2016, 12:11

Quote:

Originally Posted by MattB

It is in a freshwater lake.

Quote:

Originally Posted by matata

I know its not the most pleasant thing to be doing at sea but

Quote:

Originally Posted by Fenlander

I know its not the most pleasant thing to be doing at sea but its prob a great way to get to the bottom of it.

....albeit as said above not quite as easy at sea but that's the crucial time to gain evidence.

Fenlander · 14 April 2016, 12:21

Come on Willk... sea... on the water... whichever... still harder than in the workshop where you stand by the outboard and put things on a bench.

And salty or fresh a spark plug makes the same "plop" when you drop it in.

willk · 14 April 2016, 12:43

Quote:

Originally Posted by Fenlander

Come on Willk... sea... on the water... whichever... still harder than in the workshop where you stand by the outboard and put things on a bench.

And salty or fresh a spark plug makes the same "plop" when you drop it in.

No no, I insist I'm right!!

My definition of "at sea" does not include a scenario where you can pull a 5m boat stern to a pebbly lake shore and stand in your wellies while you change a spark plug. That's more like my garden at present!!

Fenlander · 14 April 2016, 12:49

>>>RIBnet admin team

Well yes... "of course" you're right.

Poly · 14 April 2016, 16:36

Quote:

Originally Posted by MattB

engine has a very annoying intermittent fault.

Quote:

It is well serviced by a professional outboard mech.

Quote:

He has confirmed there is no issue as far as he can tell.

To me those three things don't really add up.

Quote:

But is really only used a max of 5 hours a week.

I know you think it does not have a hard life but it must be > 10 yrs old (2 stroke), if its used 5h per week for 10yrs its also no spring chicken in outboard terms... I'd certainly not want to spend ?25%? of the new cost on a "maybe" fix for an engine that has something like a couple of thousand hours on it.

phantom 19 · 14 April 2016, 19:15

Is it an Origin (2cyl) or Hitec (3cyl)?

jeffstevens763@g · 14 April 2016, 19:48

Spark plug leads breaking down?
Hole in fuel pump Diaphram?
High resistance connection (corroded) wire.
Non return valve failure on primer bulb.

VanillaIceCream · 14 April 2016, 21:12

I had a 80's Mercury outboard do something similar, just cut out. It turned out to be a old/worn gas fuel connection from engine to fuel line.

willk · 14 April 2016, 21:20

Quote:

Originally Posted by Fenlander

>>>RIBnet admin team

Well yes... "of course" you're right.

Yeah, tell me about it. "Admin" or "Right" - which came first?

Fstarocka · 15 April 2016, 20:54

Just diagnosed the same symptoms on my 80s mercury mariner 60hp..

Since mech says everything's okay.. Look at everything before motor.

Is tank venting? Fuel line sucking air? U might have to check prime bulb, some after market brands don't work well.. Position is with arrow pointing upwards just before engine..

That's assuming mech is correct.. If not.. Might be carbs, faulty coil, plug, plug lead, switch box, the stator might be packing up..

Sent from my SM-G900M using Tapatalk

spartacus · 15 April 2016, 23:03

Quote:

Originally Posted by MattB

Or do we have to try for the CDI? At around £1,000 to replace want to make sure everything else has been ruled out.

I'd be tempted to try a new fuel pump, and primer bulb (either genuine Yamaha or Quicksilver) first before going anywhere near the CDI. I also wouldn't pay daft money like a grand for a piece of kit that you've no guarantee will cure the problem. Rule out the simple stuff first.

If you are looking on Ebay then DON'T even think about this.
New YAMAHA 40HP 50HP 2-Stroke Autolube Outboard CDI Unit 63D-85540 | eBay

Seller is notorious. You have been warned.

A1an · 16 April 2016, 07:17

Quote:

Originally Posted by Fstarocka

. Might be carbs, faulty coil, plug, plug lead, switch box, the stator might be packing up..

That narrows it down a bit.

Pikey Dave · 16 April 2016, 14:36

Quote:

Originally Posted by spartacus

Seller is notorious. You have been warned.

Shirley not Dan Cooper😏

Sh1t happens

Fenlander · 16 April 2016, 14:38

The weird thing is he now has a 100% record from 2300+ deals... turned a corner??

MattB · 16 April 2016, 19:13

Thanks for the replies so far. It's a 3 cylinder.

Believe it died again on Wednesday for 10 mins. Difficult to start running rough then all of sudden came back good again. Ran perfectly for the rest of the evening.

spartacus · 17 April 2016, 08:59

Quote:

Originally Posted by Fenlander

The weird thing is he now has a 100% record from 2300+ deals... turned a corner??

Either that or his mother is buying all his outboards!

Davie · 17 April 2016, 10:16

Do you have prime start on this?