Scott McCulloch 25

[rpsiii]

Scott McCulloch Electrical Harness Final Attempt

[geary]

Bob,
Thanks for your reply! And yes you explained it very well, even I can understand it 😄! It partially makes sense if your engine is like the early electric start 22hp SA ! They had a magneto system under the flywheel and a set of charging coils, so in order to kill (stop) the engine when the key was turned off the solenoid would go to its spring loaded position and ground out the coils ! But if it is a battery ignition and you turned the key off it would disconnect the power to the ballast resister and kill the engine ! Are your ignition coils under the flywheel or are they mounted somewhere on the powerhead ?
And if there is a Ballast resister in the system that should indicate it is a battery ignition system so turning the key to the off position disconnects the power to the ignition !

Thanks

Gary

[frankr]

rpsii, now you really got my attention. Good job on your pictorial post, but I would truly love to see an electrical wiring diagram of that system to see how it works. Do the coils receive their primary power from the alternator, and how? Are the coils under the flywheel or external? Very interesting.

[geary]

Bob, Thank you ! You solved the problem ! You know what they say about assumptions, Because I had just finished working on McCulloch 75 with battery ignition, I just assumed this engine was a battery ignition also ! We pulled the flywheel today and now see its a magneto ignition !
Why McC used a solenoid and micro switch to kill the engine is beyond me when it could have been done with a simple grounding key switch like so many other manufactures did ?
But this has been a great learning experience and just proves you never to old to learn, and never assume anything !

So thanks again

Gary

[The Boat House]

• This reply was modified 4 years, 2 months ago by The Boat House.

[JOHN HUDSON]

Hi, John Hudson, Scott Special Interest Group Leader.
Gary Orloff asked me to get into this discussion. I will do my best.
1958 and 1959 22hp Electric an Manual start motors are all Magneto ignition.
From 1960 to 1968 the 25 through 28hp motors used Battery ignition for Electric start motors. Manual start motors stayed with the Magneto. I think the reason being battery ignitions are stronger at low revs and starting. Magnetos are superior at higher revs.
1960 battery start 25hp had BALLAST RESISTOR mounted on exhaust cover plate. 1961 electric starting 27.7hp had ballast behing
ignition switch mounting. The magneto motors have no ballast resistor.
The motor in question is 1958, 1959, or 1960. Because it shows adjustable high speed jet.
Disconnect wires? Magnetos run with open circuit. Battery ignitions run with closed circuit. And the alternator/rectifier disconnect is a good idea.
Am I of help?

[jeff-register]

Way back in my dirt bike days we had a battery eliminator The bike alternator had two sets of windings, first for day use & second for night which was only hot when light switch was on. We used both windings with the battery eliminator so the alternator was at capacity all the time. The ignition was coil, cap & points same as a car…..old car!!
The alternator made enough current at manual “kick start” to fire the coils without a battery. Think you have a same system to a degree.

[geary]

Jeff,
I remember those battery eliminators from some of my buddies talking about them ! But I had a Bultaco Matador that didn’t need one, ah the good old days ! As for this McCulloch 25, once we pulled the flywheel we found it was a magneto ignition and the mystery device is a solenoid operated micro switch that grounded the points when the key was turned off ! Not sure why McC did it this way as it would have been simpler to just use a grounding key switch ! But thanks for your comments !

Gary

[jeff-register]

Gary,
Thanks so much. Mine was a SL 350 with huge overbore with 450 carbs jetted down 3 steps. Used a street bike CB cam for more power. Had more fun building it than running it. Always overheating. Didn’t think anyone remember that set-up!! Thanks for the confirmation!!

[JOHN HUDSON]

John Hudson, SIGLeader. Scott’s
22 to 25hp Model Numbers.

1958 22hp 135 Manual
235 Manual Extended Shaft
335 Electric XXXXXXXXXXXX The motor in question.
435 Electric Extended Shaft
1959 25hp I GO IT WRONG. 1959 was 25hp.
135A Manual
235A Manual Extended Shaft
335A Electric
435A Electric Extended Shaft
1960 25hp A3GB Manual
B3GB Manual Extended Shaft
C3GB Electric
D3GB Electric Extended Shaft

Talking about original points /coil/ condenser magnetos. When Suzuki went to the later ignitions on the dirt bikes (no points), they called the ignition “pointless Ignition”. Japanese English, or JINGLISH.
I guess.
John.

[Author]

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