Engine Problem.

ontheplane · 14 September 2009, 09:24

Hi all,

First post and already looking for some help!

Was out on friends boat this weekend. The outboard was running ok, but seemed a bit down on power, struggling to get onto plane. Then it picked up and ran fine, on plane etc.

As we slowed down, and got near idle it cut out completely and wouldn't start.

Took the top off, and took out plugs, held them on a bit of unpainted metal and it looked like there wasn't a spark, fuel spots appeared in the water when pulling engine over so I don't think it's fuel.

Mate was accidentally holding the HT lead when I pulled it over once though and reported getting "a belt" from the lead, so there is some power there.

Changed plugs but still no spark.

Any ideas? Hope it's not something like the elec ignition module or something expensive.

Engine is a mid-80's Yamaha 15hp 2stroke

Thanks

9D280 · 14 September 2009, 11:44

Firstly, welcome to ribnet!

Sparks - you can get a "belt" off an HT lead that won't be enough to make the contents of your cylinder go bang.
Fuel - If it doesn't spark, you'll get fuel out the back, even if it;s too lean (i.e not enough fuel).

So, You say it ran rough, then picked up, then died when at idle. That would either hint at a variable fuel supply, or a loose connection. (i.e it's something intermittent)

I would suggest that a fuel system check might be a good start. There's the obvious one of was the tank vent open, (we've all done it) then if you pump the fuel bulb when running and it bursts into life, that may hint at a fel pump problem. If that makes s*d all difference, try the "choke test" - This will tell whether your idle mix is too lean (would also explain the stalling when you throttled back). as you accelerate, momentarily "blip" the choke as you open up. If it bursts into life & runs happily at >1/2 throttle, you probably need to check your idle mix settings or clean the gunk out the carb. Cleaning the carb might not be a bad thing to do anyway.

Spark wise I guess you have the coils with built in HT leads? I assume you have a new set of plugs, if not a new set will never go wrong, If that doesnlt cure it, chase through the system looking for loose or corroded terminals. One thing to try (assuming you have eliminated fuel) is to run it in it's rough state for a few mins, & pull both plugs to see if one or the other is more oiled up. that will be the one to check. then swap each bit of the spark circuit (plugs, then leads (or lead & coil if inseperable) & see which component the oiled plugs follow. (remembering to clean both plugs before re-insertion!) You may find just swapping the plugs does it, and there's your answer.

ontheplane · 14 September 2009, 13:16

Nope, can't do that because it now won't give ANYTHING, and I mean anything, not a cough, splutter, nothing.

I don't THINK it's fuel delivery, as when pulling the engine over, after about 10 pulls, a film started to appear on the water of fuel, so I assume it's going in the cylinder and then back out through the exhaust.

I am going to look to see if I can get a spark, have changed spark plugs but still can't get a spark when I hold the plug onto the block.

I tried messing with choke, bulb went firm when squeezed, and i'd expect to get a splutter if I had a fuel problem.

Really annoying, as don't have a lot to go on.

9D280 · 14 September 2009, 15:11

Quote:

Originally Posted by ontheplane

Nope, can't do that because it now won't give ANYTHING, and I mean anything, not a cough, splutter, nothing.

Ah, OK, I thought it just died when you throttled back.

Quote:

Originally Posted by ontheplane

I don't THINK it's fuel delivery, as when pulling the engine over, after about 10 pulls, a film started to appear on the water of fuel, so I assume it's going in the cylinder and then back out through the exhaust.

All that tels you is that the carb isn't completely blocked. In an enclosed space, fuel & air needs a reasonably accurate mix to sustain burning. If for example you got a slug of crud into the carb(s) while motoring along, that could partially block the main jet enough to lea n burn weakly and totally block the idle jet. Once it died, no idle jet = no restart with a cold block.

Quote:

Originally Posted by ontheplane

I am going to look to see if I can get a spark, have changed spark plugs but still can't get a spark when I hold the plug onto the block.

Ok, that's one potential fault out the way. One thing with 2 cyl engines is that they generally aren't self sustaining with one cyl down.

Do you have a local motor factors? A spark tester would be a more sientific way of checking the HT side (A really crude thing that you plug one end into the lead, and it acts as a variable spark gap. Open the gap until it stops sparking - it's crudely calibrated with a scale that goes form "good" to "dead" with an "iffy" section in the middle. Can then compare the two & see if one (or both) of them is weak.

Like I say, with a 2 cyl youneed big RPM to keep it running if one dies. was it really really lumpy & rough before it conked out?

Quote:

Originally Posted by ontheplane

I tried messing with choke, bulb went firm when squeezed, and i'd expect to get a splutter if I had a fuel problem.

Really annoying, as don't have a lot to go on.

Bulb going hard will only prove your float(s) & their associated valve(s) are working and that you donlt have a gross leak in the fuel pump diaphragm. Might be worth (if you can't get hold of a spark tester) pulling the carbs off & cleaning them (or open the drain screws & see what falls out) , that will at least eliminate gunk as a cause.

ontheplane · 14 September 2009, 15:59

Was running fine before it conked out, although had been a bit down on power from the cold start until it warmed up - but then it was fine.

Even slowing down to the idle it seemed smooth enough.. until it just died.

Will clean carbs as that's cheap and I don't have to buy bits, have ordered a spark tester off the web so when that arrives I can check both HT leads.

One question - is there an easy "idiots guide" to checking if the CDi unit or Coil(s) have failed, as they seem the dear bit!

9D280 · 15 September 2009, 08:08

Hmmm if it "faded out" that would sway me more to fuelling, as electrical things tend to either work or not, ansd failure usually is like someone threw a switch.

If you have a coil tester, you can use a "mix 'n'match approach to deduce what the weak link is. Let's say you have 2 cylinders, and for arrgument's sake, the top shows a weak spark. then you swap the Coils over. If the bottom then shows a weak spark, it's the coil. If it stays at the top, then movve to the next component. With three cyls you nee to be more thorough with your component swaps to make sure you donlt miss something - worth writing it down.

I assume you have the coils with built in short HT lead? If so and it looks like it might be one of them, the HT lead boot will pop off, peel it back & let it dry out.

Also worth going through the ignition system cleaning all the contacts ...

ontheplane · 16 September 2009, 07:41

Thanks.

Yes I think I only have one coil with this one - it's only a 2 cyl engine.

I'll take a look at that though.

Where would I get a coil tester from?

Thanks

9D280 · 16 September 2009, 08:36

Sorry, mixing language here... coil tester = spark tester in that last one.

I just had a look at a random 15Hp microfiche from 1986, you do have 2 coils, they are just packaged in one lump of plastic. What I can't tell from the pic is how the HT leads are connected (i.e. do they come off or are they moulded in).

It looks like on the low voltage side the wires are integral to the coil pack. so if you swap them over, you'll need to swap the HT leads over as well so it still runs. If that made any sense?