Neptune alternate firing twin 5A39

[joecb]

I saw a unusual Neptune this afternoon. I don’t recall having seen one like it before. Model 5A39, an alternate firing twin, looks to be about 5 hp size and it had a WICO mag using a "wasted spark" ignition arrangement. I am familiar with the concept of wasted spark on 4 cycle engines but had never seen this arrangement used on a 2- cycle. The "Outboard Book" does not list this model in the pre war Neptunes, Although the Neptune history section does mention early alternate firing motors of 9 -1/2 and 6 HP. Is this an unusual motor, what’s the story with the wasted spark set-up?

Joe B

wasted spark… when an ignition system provides a spark during a non- compression portion of the cycle. On a 4-cycle motor (your common Briggs lawn mower) you get a spark at TDC on both the power stroke and the exhaust stroke. On this alternate firing twin 2 – cycle both cylinders get spark every 180 degrees of crank rotation, one cylinder at TDC , compression and the other cylinder a BDC ( wasted spark).

[Tubs]

The 5 Relates to horse power and 39 is the year.
I have one of the 9.5hp. models. It was the look that
got me interested in getting one. Starting it and its
performance convinced me I didn’t want any more.
I’ve been told that the smaller hp. motors (5 or 6 hp.)
not as troublesome.
https://www.youtube.com/watch?v=-_rZ4zjYgn4

A "Boathouse Repair" is one that done without having tools or the skills to do it properly.

[joecb]

Tubs, thanks for posting the pix, video. She sure seems to be running nice on your boat. As for starting issues, I’m going back to the wasted spark ignition system. have you ever encountered another 2-cycle with that arrangement? It seems strange that one would introduce a spark at the point of the cycle when the fuel charge is being introduced into the cylinder. I wish that I had had my camera to get a picture of the 5A39. It is configured similiar to your motor (but ?) the cylinders are a one piece iron casting.

Joe B

[Tubs]

Its not the spark that’s the issue IMO.
Once I learned the point gap was changing
I set them with the mag advanced and
left it there. When priming or pulling it
over any fuel ends up in the lower part
of the manifold which almost makes this
an up draft carburetor it is so low. If you
primed it or didn’t – it would never fire.
Close the mixture screw all the way and
if it was going to fire it would on the 3rd
pull. If you don’t get the mixture screw
open quick enough it will die and you start
all over. If you do get it open quick enough
and get it warmed up and dialed in and
shut it off – it wont restart. Not even a pop.
I’ve seen later models where they have raised
the carb. (2nd photo) Steve Wood bought one
at Tomahawk this year that had a choke. If
I get to go next year I’ll be interested to
hear what his experience has been. When
I did get it running it ran well but the size
and shape of the gear case moves through
the water like a cinder block. 13 MPH is
the best it would do. My 7 hp. Speedsters
would do 20 MPH on the same boat. I have
motors that are much more fun to run but
I still like the look of this thing. Its a great
display motor so I’ll be keeping it.

A "Boathouse Repair" is one that done without having tools or the skills to do it properly.

[garry-in-michigan]

That was one of the seven motors Steve ran at todays meet. He had some problems with the tank leaking, but proved that with a little ingenuity you can add a remote tank to an antique without a fuel pump – if you have a spare paddle. . . 😀

[Tubs]

That’s not it.
What is that thing he has there.
Not familiar to me.

A "Boathouse Repair" is one that done without having tools or the skills to do it properly.

[fifty20ne]

Could Steve’s motor be a Champion?

[garry-in-michigan]

Since it has the rewind starter under the powerhead, it must be a Champion. But I have never seen one like that before. . . 😳

[eltoquad]

It’s a 3H 1942 Champion. A fairly rare motor and quite a good running one. I had one years ago.

[Tubs]

I’ve never seen one.
1942 H-3 search only turns up Electra Twin – 7 hp.
If it was first introduced during the war and wasn’t
manufactured after there couldn’t many.
Anyone have pictures?

A "Boathouse Repair" is one that done without having tools or the skills to do it properly.

[Author]

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