MOPED ARMY

Varying point gap can change timing by as much as a couple degrees , advance or retard .

Just a note, adjusting the points gap does not change the location of the cam follower on most bikes. The follower is locked into position via the post in the cases.

I would double check your number. Unless you have the incorrect points, no amount of gapping should be able to mess up your timing that much.

On this bike the cam pushes a little fiber tab mounted on the same arm upon which the moveable contact of the point set is affixed. Thus if the point gap is set too small the tab (which I've called a 'cam follower because that's what it is) will stay far away from the rotating cam, only making contact when the piston has moved too far toward top dead center. The points will open for a short period (called the 'dwell angle') and then close once again as the lump rotates past.

If the point gap is set too wide, the points won't ever close, which stops the spark altogether.

Since my only feeler gauge has blades that don't fit comfortably through the flywheel holes I shall find a piece of steel clock pivot wire about the correct diameter and use that.

I shall adjust and report. The timing light is a remarkable piece of equipment.

Mark Kinsler

Points, is the power of the ignition system. The points is primary reason for kilovolts or KV. A stronger spark is the end result.

I don't know what ignition system your bike has, but in a battery/coil ignition (Kettering) the amount of time in crank degrees that the contact points are CLOSED is the dwell angle. When the points are closed the coil is being "charged". When the points open the spark is produced.

That is true. When the ignition points are closed in the Kettering system, current from the battery flows through the coil, thus building up a strong magnetic field in the core. This does not happen instantly, for a coil tends to discourage any change in the current that flows into it and will thus produce a voltage to oppose that change. So during the 'dwell' period when the points are closed the coil is allowed to take enough time to build up a substantial magnetic field.

When the points _open_, however, the current is cut off instantly, or nearly so. Again the coil discourages this change in current and tries to maintain it by producing a very high voltage across the ignition points to try to push current from one to the other. In this it partially succeeds, and that's the spark we see between the points when they open. But we really want our spark to show up across our spark plug's electrode, so we place a capacitor between the points to store most of that extra current. We get the current back, however, when the capacitor (okay, condenser) discharges its energy into the coil. That coil is surrounded by a much bigger coil, and the current from the condenser produces a pulse of magnetism in that larger coil to provide our spark plug voltage.

The flywheel magneto is another sort of animal, though the dwell is just as important. That's because our coil is used as a generator coil: it produces current when the flywheel magnet passes by and the points are closed This current circulates through two coils: one is the generator coil, and the other is the 'primary' coil of the spark transformer (also confusingly called the 'coil.') This current makes a strong magnetic field that also soaks through the 'secondary' coil, which has a zillion turns of very fine wire wound on the same iron bar as the primary coil.

When the ignition points open, this strong magnetic field that has soaked through the secondary coil suddenly disappears. Since the rate of change of magnetic field determines the voltage generated at the terminals of the secondary coil, and that voltage is around twelve thousand volts, we'll get a spark across our spark plug's electrodes as well as a dandy shock if we're touching anything we shouldn't.

The trouble is that lots of variations of these systems are possible. Sometimes the primary, secondary, and the generation coil are wound onto one big lump, as in a lawnmower or my old Peugeot moped. Sometimes the generator coil and the primary and secondary coil are separate, as on the noble Trac Clipper.

Right now it's too dark to work on the bike, but I'll open the point gap to some experimental measurement, see how things go, and report.

Everyone has been very helpful, and thank you. Please continue to add advice if you think of anything. What are the symptoms of an engine whose timing is insufficiently advanced?

Mark Kinsler

I am still trying to get my head all around timing and you seem to have a far better understanding of all the science behind it which has been an great read. I have a timing light and a timing tool and I feel like I am going to start using the light more for my bikes as the tool does what you mentioned and make it impossible to see and adjust things when you have it set. The light will require lines on my flywheel which gives me the position I am getting spark at. I can then use a degree wheel to find where the points should be opening and mark that as well. That will allow me to rotate the flywheel to get where I need to make the adjustment and then can fire up and test the change with the timing light.

The feeler type tool that I have is good for finding some measurements but I am finding it harder to set an accurate timing with these days.

Is this sounding correct?

Also I seem to be lost on which direction I would move my stator to advance/retard timing. I feel like it is this. Let's say the flywheel rotates in a clockwise direction. I would rotate the stator counter clockwise to advance the timing and clockwise to restart the timing?

Correct .

It used to be that a GED was all you needed to set timing and points. But actually I remember doing it in 8th grade.

Well I guess my HS diploma wont work because we were trained in gen ed, and not for working in a trade. I never had a "how to set points" class in any of my science classes. They were more concerned about the sex parts of a plant and the phases of the moon....

Do not panic. But it's generally best to do test rides yourself. My bike seems to have a weird, intermittent squeal and a still more entertaining clanking, but neither are coming from the engine.

Good luck and keep in touch.

Mark Kinsler

Here's a good explanation.

Maybe your efforts weren't in vain .

There is a great part of the internet that deals with exactly 'how things work' , from soup to nuts . ;)

Another piece of the puzzle to add into the whole “ spark output “ circuit is the “air gap” of the stator coils to the magneto.

I bought a barn find 1979 Puch maxi with a ZA50 engine.

The magneto was removed from the moped when I bought it.

I was chasing a no spark condition.

Followed the normal troubleshooting steps of cleaning and setting points.

As it turns out, there was no air gap of the coils to the magneto.

From what I found, the coils need to be .020 away from magneto to generate output.

So now that there is the air gap to the coils, I have spark and output for the lights.

I suspect the previous owner at some point, had the magneto off and used a flat blade screwdriver to loosen every flat blade screw behind the magneto.

A Girl Scout cookie box lid, the green o es with the mint cookies, is .020 thick.

That has to be , but , it doesn't have to be .020" .

Actually , the gap can be as close to '0' as possible without flywheel rubbing / touching the coil cores .

Seems that the smallest gap produces the best / most output . (edited)