Mis-Matched Coil Numbers

[panasonic]

Have you pumped the primer bulb when this is happening to see if it makes a difference?
Do you have a spark tester that you can hook up and see if it maybe is dropping a cylinder occasionally?

How do the plugs look?

[yellowtail]

No. Haven't touched the primer bulb but I will on tomorrow's start up and report back. I have one of those cheap spark plug testers that you clip to the engine block. Can't run the engine and used the tester, but I'll give that a try. Both plugs appear a bit oily, not the tan color I would hope for. The compression was good on both cylinders when I checked a few months back; maybe time to have another look. And the engine cold starts without the choke, which might suggest it is running a little rich. Though "cold start" is a relative term here in the tropics :-)
Thanks...

[yellowtail]

Can someone recommend a good Top Dead Center Locator, (the type that screws into the spark plug hole), for the Yammie 15hp, MSH, 2 stroke... Thanks.

[99yam40]

I have used a pencil before,
just need to feel when the piston gets to the top

[yellowtail]

First, thanks everyone for your efforts. I shot video with sound this morning but am having a problem loading it onto my computer. Pictures are easy, not so with video, it seems. Hopefully I'll have that sorted out later today and post it on the site tomorrow.

I love the idea of using a pencil to find Top Dead Center. That will allow me a way of roughly checking the timing without waiting for the arrival of a timing light, three weeks minimum. And keeps me working toward an answer to the problem. I've got a shop manual for the engine with the specs so that's not a problem. I stick the pencil in the top cylinder, don't I?

All for now and thank you...

Bry

[99yam40]

plugs out so you can turn the motor easy by hand to feel it.
but there is markings on top of the flywheel and a pointer to show TDC and degrees.
not sure how you can tell when the top plug is firing without a timing light tho

[TownsendsFJR1300]

When you cleaned the carberator ( https://www.boats.net/catalog/yamaha...409/carburetor ), did you pull specifically jets 7 & 13?

And if so check that you could see light thru them? How specifically did you clean the carb?

Did you check the fuel pump diaphragms (located on the carb) for any leakage?



I have to doubt it's your coils. Both not firing ONLY at mid range is VERY UNUSUAL.

I suspect with the wet plugs, the fuel pump may be leaking or some other carb related issue...

Misfiring can cause some very rough running, especially on a twin cylinder engine..

[yellowtail]

Trying to upload my 51 sec video to the site but it is 112 MB, so not too hopeful. Didn't get the message to use Flicker until after I started. But the video clearly shows vibration at slow speed that evens out at half speed. You can hear it too. I tried pumping the primer bulb but that did nothing. As far as cleaning the carb, I completely disassembled it and soaked it in carb cleaner. Then I cleaned with a soft bristle brush and scrapped all the orifices with thin brass wire followed by a good hosing of carb cleaner straight from the aerosol can, under pressure. That's the approved Dominican way and the best I can do :-)
I did inspect the fuel pump diaphragm and couldn't detect any damage. I don't see any fuel leakage anywhere.
Got my timing light on order, but that'll take three weeks to arrive if I'm lucky. If I'n not lucky, I'll never see it and some Dominican will be using it for his music videos.
Okay, just got: "Error: PHP Max Post Size has been exceeded." Let me try Flicker and post the link.
Thank you all...
Bry

[yellowtail]

Hey Townsends: Just wanted to confirm the fact that YES, I did pull and clean jets 7 & 13? But Jet 13 has me concerned. It's a short tube with two collars spaced from the ends. But the spacing is different. One collar is closer to the end of the tube than the other. In the diagram you kindly provided, it would appear that the collar positioned closer to the end of the tube, is faced down. Looking over my notes that I took when I disassembled the carb, my Jet #13 is the other way around. And like I said, I',m not going by memory here. Should I be concerned?
Bry

[TownsendsFJR1300]

Hey Townsends: Just wanted to confirm the fact that YES, I did pull and clean jets 7 & 13? But Jet 13 has me concerned. It's a short tube with two collars spaced from the ends. But the spacing is different. One collar is closer to the end of the tube than the other. In the diagram you kindly provided, it would appear that the collar positioned closer to the end of the tube, is faced down. Looking over my notes that I took when I disassembled the carb, my Jet #13 is the other way around. And like I said, I',m not going by memory here. Should I be concerned?
Bry

All those jets SHOULD BE CLEAR... And that jet (as well as others), will ONLY GO IN ONE WAY. You should be able to zoom in on the parts picture and may see the direction..

Carb spray is good BUT you have to make sure ALL those TINY, sideways orifices are clear. Look thru them from the side, (obviously you can't see 90 degrees to the main hole), but blowing from the larger hole should blast out the sides too...

Often, the holes are so small I have to use a cut off piece if wire from a wire brush, clamp it in a vise grip (yes it's that small) to clear a jet.

*Did you happen to inspect the fuel pump diaphragms while the carb was apart?


Also, you can try loading your video on "You Tube". I never have but there's real long ones there.


Zooming in and enlarging (carb body is above the jet) , jet #13, yours sounds to be installed correctly:

[yellowtail]

Yep. I cleaned all those little holes, one by one, with a thin brass wire. Then blew them out with carb cleaner using the nozzle tube than comes with the can. I checked very carefully and saw light through each of the orifices. There is no doubt in my mind that they were clean when I reassembled the carb. And I have added Injector Cleaner to the gas since then. But I still think jet #13 is in upside down, long end down. I may not sleep until I take the carb off and check :-) The fuel pump was stripped down, inspected and blown out as well.
Still working on the video. Timing light on order. Next I'll do a compression check... one step at a time...

[yellowtail]

Hello to everyone.

Poked around on the Yammie 15 again this morning. Compression: Top cylinder, 120 #'s. Bottom cylinder, 124 #'s.

Plugs are a little oily but not gummed up with gunk. I replaced the Pilot Screw less than a year ago but might give it a twist half a turn, but I'm sure that's not my problem.

I used a pencil to check for TDC and the marks lined up on the flywheel. So I'm waiting for my timing light. Being there's no 12V battery, I ordered a timing light that runs off two 'D' dry cell batteries. Anyone have any comments on that style of timing light? If it works well it will save a lot of work running leads from the sailboat batteries plus, I figure I can use it on the water to check the timing at speed.

Didn't remove the carb to check on the position of that jet. But when I get it off next, I'll pull the reed valves as well and see if they are closing tight... no sign of blow back so I'm hopeful they are in good shape. The motor is about ten years old, but gets used daily, so things are going to start wearing out. And I wanted to mention that the prop is in good shape and there's plenty of water around here and I don't ever remember bottoming out.
Bry

[yellowtail]

This should be the link to Flickr: https://www.flickr.com/photos/171468...posted-public/
If you can open this, you will see that I missed cold start up. That was choke and a single pull. To me, it sounds like idle is normal. But under initial power-up, you can see the vibration when looking at the "15 hp" on the front of the cowling. Plus, hopefully the sound. As I power up, things smooth out at about half speed.

[TownsendsFJR1300]

Interesting to say the least. Idles smooth enough

When it's knocking the worst (I think just above idle), make note of the RPM's. Ground out one spark plug wire at a time to the block and see if the knocking is LESS (engine running).

Do this for each cylinder. *Sounds like a rod knock initially...

You could likely do this tied up tight to the dock as the RPMs don't sound very high and that knocking is definitly noticeable


Re-watching the video, it almost seems as well like your missing a tooth in the lower unit. Once your in gear, the knocking is horrible, pointing towards the LU.

If you can tilt the engine out of the water(off of course), stick it in gear and try moving the prop. You may have to rotate the engine by hand the full 360 degree's . Should there be a tooth missing/damage to the LU, you should feel a large gap in movement in THAT particular area with the prop...

Definitly sounds as if something fatigued and broke...

[yellowtail]

Thanks Townsends... let me look at this and get back to you. Glad the video worked out.
Bry