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15HP Two stroke #1 not firing

--JR--

New member
I've only owned this motor a short time, but the first time I ran it it seemed to run "good". I just had it in a static garbage can with water test, no real power laid down or on boat testing.

I pulled the flywheel and installed a stator to add a charger to the motor. I bought an OEM Mariner part that fits this motor and it installed without issue.

Fast forward a month and I've now got the motor mounted to the boat and tried to run it. It's really hard to start, shakes like a bastard and only fires on #2 cylinder. Confirmed by pulling #1 plug wire with no change to motor's idle. Pulling #2 wire and the engine dies. Plugs looked pretty ugly so I put new plugs in it, no change.
#1 coil resistance matches coil #2 on the primary and secondary winding, so I think the coil is ok.

I have not completed the generator rectifier wiring yet and I have not run the motor since installing it. So I don't believe the stator it's self is causing a problem.

I don't believe the flywheel can be put on backwards or in a different way as it had a key-way. But I'm 100% a newbie when it comes to marine engines. I have worked on small motors and a lot of cars, but this whole marine engine gig is new to me! heh...

Ideas?
Thanks!
 
Sounds like a bad coil. Try swapping the two and see f the problem follows to the other cylinder.

Jeff

PS: Your resistance test won't necessarily point out a short under full voltage.
 
When you pulled the flywheel, did you use something that grabbed on the edges?
You aren't supposed to do that....can cause the magnets to detach.
Magnet may have shifted...causing unbalance.
No cost to check.
 
Sounds like a bad coil. Try swapping the two and see f the problem follows to the other cylinder.

Jeff

PS: Your resistance test won't necessarily point out a short under full voltage.

Duhh! That's a great idea. I'll see if I can find time to try that tonight. I was hung up that each coil has a specific high voltage lead length. I'll just unbolt it from the block, but make sure it's still got a ground for it to reach.

-JR-
 
Crap, problem stayed on cyl #1 when I swapped coils.
Took a couple pics of the side of the motor and where all the coils are installed if it provides any clues. You can see both magnets there and they seem to be in their place.

Also measured back into the ignition control unit. It meters open circuit on CYL 1 and 2 with an ohms meter and reads .5 on a diode test on CYL 1 and 2 as well. That seems pretty good sign so far.

Double checked the wiring color coding seems to be correct from the coils into the ignition control too.
IMG_2418.jpgIMG_2419.jpg
 
You say "You can see both magnets there.....".
It is hard to tell from your first photo....but, the two magnets should be on opposite sides of the flywheel...180 degrees apart!
Are they?
 
Magnets! That's it. They are indeed next to each other. The one pictured on the right, below, is actually loose when I gave it a nudge with my finger. The one on the left is fixed in place.

I'm guessing I had some interference between stator coil and one of the magnets when I was fitting it. I seem to recall I have it a test spin to check it before I tightened the flywheel bolt. That probably did it!

So now the question is...
How do I verify they are in the correct locations?

Edited the photo to make them clearer
edit IMG_2418.jpg
 
Take the flywheel off.
It should be very apparent where the magnet that separated came from.
You have 2 options....try to epoxy the magnet that separated back in place.
Or, purchase a new flywheel.

There are 2 different flywheels for this engine.
On this site, click on Boat Engine Parts, Mariner, enter your serial #.
Compare the top of your flywheel to the ones in the parts diagram.
It looks like one of them is NLA.

If yours is NLA, you can epoxy or go on eBay and get a used one.
To epoxy, use small dabs of epoxy in a bunch of different places.
Put the magnet back in place and push hard...you want the epoxy
squeezed to a very thin layer. If it isn't, the air gap will be wrong.

Let the epoxy cure and put the flywheel back in place.
 
The flywheel and stator merely generate the amperage to fire the plugs; the switchbox and trigger coil determine the when and where it goes.

Try checking the resistance of the trigger coils with your meter.

Jeff
 
After you repair magnet, just swap the trigger wires(brn/wht & brn/yel) to see if problem stays..if so replace switchbox. Make sure you use a spark checker as this will cause mota to backfire.
 
Cleaned up and repainted the flywheel, was looking a little "salty". Replaced the magnets to their intended positions with a little epoxy. Reinstalled the flywheel. Fired up on second pull and it's running like a top again!

Thanks very much guys!

I have another question about this type of motor, but I'll start a new thread for that.
 
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