yamaha 25 1980s ignition fault

[bartiny]

Originally Posted by stigoftd

your coil you say hasnt got any no's on if you take it off look at the reverse is should be on there as it seams that if it is on the tiller side of the engine they go on upside down the other side it is on show
hopefully ile be givving her a run down the river sometime this week nd report back

yep your right, I had already sussed that the coil had been reversed, good luck with the test run

[stigoftd]

just got back from the test run and she started first pull then ticked over sounding it was on 1 cylinder reved up and fired on both running perfect
tick over on one put in gear and slowly picked up revs untill the point where it fired on both and off she went pushed the boat 25knots puring lovely then throttle back a bit of a splutter and back to tick over and 1 cylinder

think the timing may be more out than i thaught
any thaughts ??

[Transporterman99]

Remember I know nothing about two strokes once they get fitted to boats- but it does sound like poor HT spark to me. If it was a 70's Japanese bike I'd go for HT lead or spark plug cap. As revs increase the spark gets fatter and can jump poor connections. (I'm assuming old boat two strokes still had such things!)

[Transporterman99]

On early single cylinder Yamaha bikes (as far as I remember!) you altered the points gap to advance/retard the ign timing but on yours you probably need to loosen and turn the whole plate (affecting both cylinders) making the fault less likely to be timing.

Make sure the points gap is to spec before checking the timing of course..

[bartiny]

Spark plug NGK-B7HS, Spark plug gap 0.5 > 0.6mm or 20 > 25 thou.

If the plugs have not been changed it would be worth a try first.

I think that I posted a couple of pages on the way to set up the timing, but if you need them again or more info let me know.

[bartiny]

Originally Posted by Transporterman99

On early single cylinder Yamaha bikes (as far as I remember!) you altered the points gap to advance/retard the ign timing but on yours you probably need to loosen and turn the whole plate (affecting both cylinders) making the fault less likely to be timing.

Make sure the points gap is to spec before checking the timing of course..

Thanks again for the gauge, top notch

The timing is set on no.1 cylinder (top 1), slacken off the timing plate, set the points gap to 0.35mm or 14 > 16 thou. once gapped rotate the flywheel untill the piston is 3.35mm or 0.132thou BTDC (you need a dial gauge) at that point the points should just be breaking contact, you get this bang on by rotating the base plate, you really need a meter, but the trusty 'fag paper' is just as good (IMO) when you are happy without moving anything tighten up the base plate, then all you have to do is set the points for no.2 cylinder (bottom) so rotate the flywheel untill no.2 cylinder is 3.35mm or 0.132thou BTDC at this point again the points should just be breaking contact if not you set these up by adjusting the points gap only, so it does not matter what the gap is just that it is breaking contact.

Now my head hurts, hope that makes sense

[stigoftd]

yep the plugs are new but i will try another set of new ones to eliminate them also change the ht lead and plug cap
and re check the points
other wise it runs spot on and sounds smooth just as long as i want to go full throttle
the only thing is the boat has a flat front so every wave you get drenched and taking the kids and misses down the river to plymouth next week for the annual fireworks competition in plymouth sound better not soak them on the way down

[bartiny]

As far as I know the HT leads are moulded in and cannot be changed

[stigoftd]

some are on a thread others glued in ans some moulded like you say - never thaught of that

[stigoftd]

had 40 min fidling arround with bits and pieces today and re checked the points had to re adjust one also there seems to be alot of play in the stator linkage which i have adjusted a bit and she sounds to be running as she should now off to do round 2 of sea trials tomorrow have a few other minor adjustments to do on the water hopefully off we go
ile report back on return

[stigoftd]

was on the slip at 5am this morning had the whole of the river to my self and milpond conditions slack tide so launched started first pull ticked over a little high so had 10 checking and adjusting on the slip then a 1 mile run up river at 1/4 throttle she pured perfect then the 1 mile back on full wot i we done 1/2 a mile and the coolant stoped so whiped out the thermostat to find it totaly full of salt lumps and in a bad state so removed and off again re done this run again and not a missed beat all the way round and plenty of coolant exiting

so off we go ile be ordering up a new fuel diaphram [for the sake of it ] and replacement thermostat
thanks for all your help bartiny and transporter man

[bartiny]

so off we go ile be ordering up a new fuel diaphram [for the sake of it ] and replacement thermostat
thanks for all your help bartiny and transporter man[/QUOTE]

Thanks, You are welcome,
I would not be too hasty about ordering a new thermostat try it in some hot water first, if it opens then leave it, they are pricey.

The fuel pump diagphram is a different matter good to carry as a spare if not needed.

Sounds like you have cracked the missfire then, good one.

Good luck

[stigoftd]

Originally Posted by bartiny

I would not be too hasty about ordering a new thermostat try it in some hot water first, if it opens then leave it, they are pricey.

The fuel pump diagphram is a different matter good to carry as a spare if not needed.

Sounds like you have cracked the missfire then, good one.

Good luck

the thermostat is knackerd but if they are too much i wont bother replacing my mariner 15 hasnt had one in it for over 7 years and never given any trouble also done the same with another yamaha 20 before but would like to replace if i could find a cheap enough one

i have never had a fuel diaphram go on a outboard but always like to replace them just on the side of caution
the final adjustments on the slip sorted the last of the faults on the missfire side it was a pain the but well worth it and i even learnt something in the process

[A1an]

You really should replace the stat, your engine and oil is designed to run at a certain temperature.

If you are too tight to buy one then you can send me your old one and il see if I have one to match it. I replace the stats as soon as I buy an engine but I keep the old ones if they still work. A used stat is better than no stat.

[stigoftd]

Originally Posted by A1an

You really should replace the stat, your engine and oil is designed to run at a certain temperature.

If you are too tight to buy one then you can send me your old one and il see if I have one to match it. I replace the stats as soon as I buy an engine but I keep the old ones if they still work. A used stat is better than no stat.

ime not too tight to buy one but when you get a price of over £70 for one then i refuse to pay over inflated prices and will just wait till i get a more realistic price when the engine will run perfect without it
although if you have one going at a reasonable price ide be more than happy to buy it off you

[bartiny]

Originally Posted by stigoftd

ime not too tight to buy one but when you get a price of over £70 for one then i refuse to pay over inflated prices and will just wait till i get a more realistic price when the engine will run perfect without it
although if you have one going at a reasonable price ide be more than happy to buy it off you

This is the cheapest one I can find in the uk, still pricey for what it is, I think its the right one.

YAMAHA OUTBOARD MOTOR 25HP - THERMOSTAT - 6H7-12411-01 | eBay
HTH

[A1an]

Yam stats fit a multitude of HPs.

I might have one to match but I wouldn't know unless I had yours in my hand.

Don't want anything for it, I'm Scottish not a Yorkshireman.

[stigoftd]

Originally Posted by A1an

Yam stats fit a multitude of HPs.

I might have one to match but I wouldn't know unless I had yours in my hand.

Don't want anything for it, I'm Scottish not a Yorkshireman.

ile re find the old one but know the top plate has corroded off - well it fell off when i took it out

[HughN]

Originally Posted by A1an

I might have one to match but I wouldn't know unless I had yours in my hand.

[A1an]

Originally Posted by HughN

But I suspect mine will be a good bit bigger