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Hi
I've just heard a rumour about 'the middle coil getting tetchy' after a few years then begining to misbehave.
Now my motor will run fine on idles and most speeds, but after a while on full bore sometimes it just dies. Then after a few minutes will fire up again, only to repeat the process if maxed. 4/5 full seems a bit more stable.
So, checking the obvious items like cooling water flow, fuel lines without kinks and filters free of crud n water revealed nothing wrong. Dammit!
I have yet to replace/service the impeller. I'm hoping that increased water flow (the pptelltale is a bit weak...) will resolve my angst, else I thought there is nowhere else to go! (& new plugs)
Now this rumour has me thinking perhaps I have a ghost in the machine...

Is it carbed or fuel injected....when it dies at high revs does it stop completely or lose power??

Prolly some crap in da carbs.
Yank'em. Clean'em. Put'em back.

As Billy Bob said in "Slingblade". Ain't got no gas in it, um humm.

http://www.youtube.com/watch?v=G-tCIRJH9p0

it's an NS50SD.. mixes its own oil and has carbs.
Mucky carbs hate that job. It has to be one of the next stages though it doesn't seem to quite fit the problem.
Anyway, it loses power big time, to the point of stopping. I would have said fuel starvation.. though it seems independant of whichever tank I use, and there is plenty available when it has happened. (About 3-4 times now)
It's the sort of headache one can spend ages chasing...

Oh brilliant..
I've just spotted a solenoid attached to the choke.. it's not been wired in or I've never seen the switch for it
no more leaning over the side fiddling with knobs any more

I don't know a thing about your particular engine, but It sounds like a filter problem, not a carb problem. Are you sure that there is not another filter in the system that you have not changed? There are usually other filters, some of them not so obvious.

~Rich

restless wrote:Hi
I've just heard a rumour about 'the middle coil getting tetchy' after a few years then begining to misbehave.
Now my motor will run fine on idles and most speeds, but after a while on full bore sometimes it just dies. Then after a few minutes will fire up again, only to repeat the process if maxed. 4/5 full seems a bit more stable.
So, checking the obvious items like cooling water flow, fuel lines without kinks and filters free of crud n water revealed nothing wrong. Dammit!
I have yet to replace/service the impeller. I'm hoping that increased water flow (the pptelltale is a bit weak...) will resolve my angst, else I thought there is nowhere else to go! (& new plugs)
Now this rumour has me thinking perhaps I have a ghost in the machine...

During my 2nd season with this boat, I had motor issues similar to your description, both before & after fuel treatment, replacing fuel lines & primer bulb and installing an external fuel filter / water seperator. I eventually discovered a problem with the factory in-line fuel filter housing (pill bottle size under the hood). The inlet barb had a crack that was leaking fuel at rest, thus drawing air while running. I've removed this filter and have not had the same issues since. Replacing spark plugs & water pump impellor have been only other service on this Tohatsu thus far. (Knock-on-wood)

Here's another possibility to consider. In brief make sure the oil injection is working.
It comes from a painful (expensive) experience with my Tohatsu 50D.
Your symptoms sound very similar to my experience which resulted in an aborted trip and an engine rebuild.
What caused the problem was an air-lock in the oil injection tubing resulting in no oil being mixed into the fuel. This was the first trip after sitting all winter.
It wouldn't run at full throttle but I was trying to catch up to some slower boats so I charged on. After more than an hour it stopped abruptly. It did restart it several times and it would run for 10 minutes or so. After several repeats of that it wouldn't turn over. After a few minutes it did restart but I was going home by then. I believe the engine was trying to protect itself from overheating - the alarm buzzer should have been sounding but it didn't. There were no symptoms of overheating- no smells or steam from the cooling water outlet. I finally did notice that the oil level in the reservoir seemed to be unchanged from the last top-up. I mixed oil into the fuel tank and managed to get back to the dock. This was a $1600 lesson.

no oil... ouch!!
I (fingers xed) don't think it's that thankfully as it behaves fine when not flat out, and requires reasonable topping up. I see there is a sensor in the oil pot... anyone know what this is about? A low level warning would be good, as would a way of testing buzzer functionality.
Thanks all fot the input. A colleague here told me the diaghram on the fuel pump had also developed a crack, but since sorting that and the middle coil he's been problem free.
I'll check my filter lines and post any useful findings.
Thanks for the input. All valuble info, thanks.

I have spent a fair amount of time babying that engine.

The fuel pump barely, and I mean barely provides enough fuel from the tanks when working properly. any cracks or leaks in tubing or fittings will result in fuel starvation......typically at 4300-4500 rpm seems to be the case.

a single coil will not kill the engine.....as this beast will run on 2 cylnders......... not pleseantly either.

A quick check by pulling the boot and plug will show if you have spark,

I think you will find that you are not getting enough fuel at that rpm and sucking the filter/bowls dry.

That does seem to fit the bill W&W. Is there any way of improving this setup? Other than making sure all lines are in tip top condition I suspect not
At least that can be checked.. hadn't thought of looking to see if the filter bowl was empty. Easy enough to do and a pretty direct diagnosis
I think I'll post all this info collated up as a mod... perhaps it would be a good idea for others to do the same with their various overboards?
I actually know that one of my fuel tank lines is ripe for replacement, though as yet not smelt any leaks. Got so many other more interesting bits to buy before getting round to that!

Oh, as a by the way... I've just seen a manual start pullcord setup on ebay... now the idea of a backup start does appeal to me. Does this engine require 12v to start the ignition or is it magneto? Anyone got a man/elec motor? is there a way to get round the elec.trim/lifter without power??? all these questions.. what can I say, these are the voices in my head

You want I should scan in my tohatsu M50D manual?

Restless-
Without knowing what the "manual start pullcord setup on ebay" is, your motor is manual start capable already. With the engine cover off, there is a plastic flywheel cover that is bolted to the engine block. Remove this cover. I've always left mine off. A length of rope, 24" - 36", (should be included with the mini tool kit that came with the OB) with a knot at one end will wrap in the groove on the top of the flywheel, allowing you to pull start the motor. Ignition (key) must be on.
On the transom bracket - at about the waterline - there is a screw for manual release of the hydraulic trim / tilt .

I don't have a scanned copy of the manual, but if you need a scanned parts book for the 50D, I have one.