Logo
FULL SITE MENU

yam mariner 40 intermittent misfire

J

jwatson

New member
hi all. i have recently purchased a small 14ft marina with a circa 1979 mariner 2str 40 outboard. the engine runs but has a bad misfire. however, i took it to ullswater in the lakes over the weeked to try and get a better idea of what was going on. the engine spluttered away after a difficult start. we chugged around for a bit then it burst into life & we had full throttle!! the speed limit on the lake it 10mph so unfortunately we had to knock it back down again. it then started chugging again and then we ran out of juice & had to get towed :D here are some pics which may help as im not 100 % on model (yam enduro 40?) or year. cheers.
i know there is no plug lead in the pics! had to joint it as it was split. was giving a spark when tested but not the biggest.



 
I would start with replacing the coil lead.Taping over a split doesn't really work.And if the carburettor hasn't been cleaned in awhile,give it the once over,blow it out with a bit of compressed air.
There should be a number on a plate on the transom bracket beginning with either 676 or 6E9. Older Yamaha 40FM's painted in Mariner colours
 
Thanks for the reply!! There's a code that says "Y1 676-00" on a number of the engine parts but that's all I can see. Does this help?
I realise the ht lead should be replaced but it isn't removable from the coil. A full u it would therefor be required and I'm having great difficulty if finding one with the same part code. My mate reckons it would be possible to swap out the entire ignition system for that of a later model. What would be involved with this?
In also trying to remove the flywheel so I can inspect for any obvious signs of wear / damage & re set the points but cannot see any way to hold the flywheel still whilst removing the virtually seized crank bolt.
I have cleaned out the carb & pump but not tried it yet as I'm waiting on a new pull start.
Thanks again.
 
I doubt if there's any "points" under there!

You problem is a bad coil. Buy one new one and try it at one position. If not change, try it on the other cylinder. If still no change, buy a second new one.

Jeff
 
Thanks Jeff. I can see the points through the holes in the flywheel. I've been looking everywhere for a new coil with no luck!! Would one from a later model suffice? Ignition isn't my strongest subject but how different can coils be?
thanks again, this forum is miles better than the other I've been trying!!
 
as luck would have it ive just found an exact match on ebay which had only been listed for a few hours!! lets see how we get on.... fingers crossed but not getting my hopes up!
 
If it's a 40A it'll be '77/'79.And I would have said the same as Jeff no points.Though in saying that, I see a breaker listed and absence of a CDI box could indicate points. Good luck on the coil.
 
Yep its a 40A and points gap at .014 +/- .002. It has 2 sets of points & condensers and 1 ignition coil under flywheel. Also there is a diode between coil and wiring harness to flywheel so check them also(top is reversed from lower) Yamaha called this a bendix type magneto ignition system
 
Thanks guys, what a forum!! I would love to be able to post a photo of the magneto etc but can't get the flywheel crank bolt undone!!! There is no way of locking the flywheel!!! I will set the points & have a play around when the new coil arrives ie try both coils on both diodes & see what I find!
Thanks again!!
 
Thanks but mine has the code F6T405 so I went for that one. I'm not sure what these codes mean and recon they'd both work!
believe it or not Jeff I tried that and bent my grips!! Will give the nut a good soaking. I've been told diesel is good but may drip into the magneto. Plusgas may be the sensible option!
 
You could make a tool,flywheel holder.Two pieces of 4 or 5mm x 30mm flat iron.One about 600mm long the other 200. Drill two 10mm holes in both pieces,one either end of the short bit and one at the end of the long bit and the second hole about 200mm back.10mm bolt to pin them together.Remove a couple of those studs visible in your pics and put the "tool" on and bolt it up.
 
hi guys! right, an update!! I managed to get the crank bolt undone with heat and using TWO grips on the flywheel rim. went blue in the face pulling on my 600mm breaker bar & fell on my arse when it finally went!!! now I cant get the flywheel off! ive got a puller but it doesn't seem to be up to the job. the central screw which turns is twisting & the centralising point is being mashed on the end of the crank!! have left it soaking in wd & will try again tomorrow.
 
as for the coil, it works. but something is really amiss. think its to do with the wiring up to the top cyl coil. I get a spark when its connected to the bottom cylinder, but only when the top cylinder is wired up!! the spark isn't the best either. the top cylinder is proving no spark at all. what should my points gap be? hopefully if I can get the flywheel off something may become apparent.
 
The #1 cylinder breaker should be set at 0.3-0.4 mm. The #2 cylinder breaker needs to be adjusted to open exactly 180 degs. from the #1. It is quite a set-up to get it to that point, involving some specialty tools. Once you get in there, check the wiring, test the coil and the condensers, and clean the contacts. You should probably leave it at that, if you don't need to replace any parts under there (there may also be a lighting coil under there to charge your battery).
 
H. I. McDunnough said:
The #1 cylinder breaker should be set at 0.3-0.4 mm. The #2 cylinder breaker needs to be adjusted to open exactly 180 degs. from the #1. It is quite a set-up to get it to that point, involving some specialty tools. Once you get in there, check the wiring, test the coil and the condensers, and clean the contacts. You should probably leave it at that, if you don't need to replace any parts under there (there may also be a lighting coil under there to charge your battery).
Click to expand...
thanks guys! I know how to gap the points but how do I alter when they open? My flywheel puller is now broken so will be taking it back!! Can anyone shed any light on why the one spark I do get ceases when the other coil is disconnected?!!! It's not co incidence I've tried it loads of times now!! Also when wiring up the other diode into the working coil it does not fire. I guess it's also faulty but what do these diodes do? Prevent run on?
If you would be so kind as to describe how I should test the mentioned parts I will do so ASAP!!
Thanks for the tip Jeff but I've read not to hit the crank or flywheel. Is this just over cautious? Ta
Thanks
 
Last edited:
OK, gapping the #2 breaker does alter when it opens. The #1 breaker was set when the magneto base(timing) was set.
The diodes keep the engine from running backwards. They can be tested with a VOA meter. It should read infinity.
The breakers only allow current to flow to the secondary coils when open. You should really find a manual for accurate testing proscedures.
 
hi again guys, thanks ever so much for all the help!! I finally got the flywheel off!! mashed the puller in the process but it came off! so I spent a few hours inspecting & playing around with the ignition system. I couldn't get a spark on both plugs for the life of me, it was either one or the other. I removed everything from the flywheel and noticed there was a bit of oil that must have weeped from the top crank seal. I cleaned everything, put it back together and the last time I checked it worked!! two sparks!:eek: managed to get it started but kept dying. id pull the starter, it would run for 1 second then stop. turns out the pump has had it as when I pumped it manually it ran continuously. I noticed when it started to warm up the revs began to rise. im guessing the mixture needs adjusting from when I rebuilt the carb? so as per usual I ran out of time and didn't get chance to fill the tub and get it running properly for a while but so far so good I guess! no doubt it wont work again when I get to work on it again!!
 
Back
Top