15 HP Johnson no spark

[Glenn]

Hey Guys

A friend has what I would guess would be a mid 80's 15 Hp Johnson. The one that looks just like the 9.9 with the angled cowl. It has electric start, cranks over fine and is getting fuel but no spark on either plug. We pulled the flywheel to check the points and they look fine, no pitting. Not very knowledgable in these ignitions system or how to test them. It seems to have 2 magnetos(?) close together connected to the points with condensors and a 3rd one across from them that there for the small charging system? The 3 of them are hooked to a round thing that I would guess is a rectifier by 3 yellow and blue wires. Each plug has it's own coil on the back of the motor fed by 2 large blue wires. Looks like the kill switch is hooked in paralel with the coils so we disconnected it to see and still no spark. I know that there is very little to go on here but was wondering if there are any commun ignition problems on these little motors or things I can test. I'll have a few pics of it by Sunday and the year of the motor.

Glenn

[Bill Rogers]

A 9.9/15 with points has to be 1974 thru 1976 model. Went to the CD2 system beginning in 1977.

What you have is an energy transfer magneto. The coil under the flywheel is the driver coil. Each side of the driver coil is connected to a set of points. With both sets of points closed, current is generated in the driver coil by the magnets in the spinning flywheel. When 1 set of points opens, the current is suddenly diverted to 1 of the external ignition coils (this is the energy transfer part- energy is transferred from the driver coil to the ignition coil when the points open).

The other coil(s) under the flywheel are for battery charging and have nothing to do with ignition.

If either set of points is bad, you won't have spark on either cylinder. If one of the condensers is bad, you 'll have no spark on just that particular cylinder. Since you have no spark on either cylinder, and you've already ruled out the kill switch, I'd say you have a bad set of points, or a bad driver coil.

You can check the points, driver coil, and ignition coils with an ohmeter. I don't remember the specific values for the coils, but you're generally looking for opens or shorts.

btw - the kill switch simply shorts the 2 sets of points together to kill the engine

[Glenn]

Bill Rogers

Thanks very much for the info!

Glenn

[capnzee]

My money says this engine has never had a set of points and condensors replaced since the engine was new. For about $30.00 you can replace both sets of points and the condensor. If this doesn't work you can then replace the "driver" coil. You will not have wasted your money on the points and condensors. Make sure that you have set the points at .020, and that you donot contaminate the contacts on the points with oil, dirt etc. Clean the entire plate after removing the old points and condensors and before installing the new. Then set the points at .020 with the crankshaft cam lobe at its high point (you will see the word "set" on the top of the cam lobe. capnzee

[MattGreen]

The above advice is excellent. Those driver coils DO pack it in fairly regularly if they're original. Make sure you check the kill switch before buying any more parts. You should always eliminate the switch as a first step when looking at a complete no-spark situation. Be patient when installing points on this motor; they're not quite so easy to gap as regular magneto ignitions.
While you're deep into the ignition, check the external coils for cracks - common if they are original. All the parts you need to repair this motor are still available from you BOMB dealer.

Matt

[Glenn]

Capnzee, Mattgreen

Thanks for the info guys! Hopefully this Saturday We'll have a good idea what's wrong. there is an OMC delaer not too far. I'll snap a few digital pics.

Glenn

[Glenn]

Thanks again guys for the info. It was the points. One of them had a fair amount of resistance across it. Cleaned them up, re gapped them then had good spark on both cylinders. Fired right up and ran great!

Glenn