HOME and how to join Forum Open Area General Scott topics Just bought a Scott,can anyone help? Re: Sparks

Roger Moss

Hi Dan
I have written the following in simple terms.
Please accept that this is not meant to insult your intelligence, but just to be sure that I did not miss anything.
By what you describe, your electrical apparatus is made up of two distinctly separate devices, They are attached together only because they need to be rotated by the engine and if you put them together, it is only necessary to provide one input drive from the engine.
The two elements are
1) The magneto. This is a totally self-contained generator of high voltage current to make the sparks. It has, in this case, two “High tension” leads that go directly to the spark plugs. A magneto is also usually provided with a connection for a wire that can go to a “Kill” switch on the handlebars. When such a switch / button is activated, the magneto is unable to make sparks and the engine then stops.
2) The dynamo. This is a DC generator that makes the electrical current for lights, horn etc. via the battery. There will be a regulator to control the amount of electrical current produced, so that it makes what is needed, no more, no less.

In your case it would seem that you have a problem with your magneto.
This is a common problem that can have several causes.
Let us consider the simplest options first.
Take off the end cover opposite to the drive end.
If it is oily or dirty, remove the centre screw and take out the rotating centre element that contains the contact breaker with its fibre shoe.
Now clean it up and check that the contact points are clean and do not have either lumps or holes in them.
If there is a lump, try to use a stone to rub it off by hand, not on a powered grinder..
Re assemble and set points when the contacts are open to 0.012″ / 0.015″
Check that the leads to the plugs are in reasonable condition
Remove the connector pieces where the leads to the spark plugs connect to the sides of the magneto body.
There are carbon “brushes” with springs behind them that rub against a non metallic ring with two strips of brass let in to it.
Check the carbon brushes are not broken, are not swamped with oil, and are free come out of their housing if you push them in against their light springs.
See if the area they rub against inside is clean.
If not, put a rolled up bit of rag down the hole and rotate the mag by turning the back wheel in gear on its stand, or by kick starter.
If it is very dirty, make a wad of fine wet and dry paper and try to push it down to clean up the track.
Please be sure not to lose bits inside if you can help it.
Re assemble
Take out spark plugs
Connect leads to plugs but do not allow leads to touch engine
See if you can lay the plugs so that the body is against the engine, but not the top terminal.
Now kick the bike over and see if there is a spark
If not, it could be that the rotating part called the armature has a break in its windings of fine wire. This would be unfortunate, as these are quite expensive to have repaired.
Do not panic yet!
Sometimes, if a bike has been stored in damp premises, the damp gets into the mag windings and causes problems.
In past years, it was a custom to take the mag off the bike, if it was not going to be used during the winter. The mag was put in the airing cupboard to keep it nice and dry until it was required again.
If you try what I have suggested and still have no sparks, take off the mag and put it in the airing cupboard for a couple of weeks while you check out all the rest of the bike.
I have known the mag to revive if nicely dried out.
If you want to know more, I can lend you a book on magneto’s and dynamos.
If you wish this, email me at
and give me your address.
All I need then, is your promise that you will return it at some point, so it will be available for someone else.
Do try and be patient.
It is very difficult when you start.
So much to learn.
Sometimes due to limited funds you may have a bike that has a few problems.
And to add to these difficulties, it takes time to build up a good toolbox.
Remember, we have all been there before you.
With Patience and persistence you will succeed
Kindest Regards
ps their might be a few items of info on my website that might help.
In fact I think I will put some of these answers on it, but I have been too busy to do much with it recently.