Set Ignition Timing With the Squarker

How-To: Build the Squarker device to help set ignition timing.

| August/September 2014

  • The simple-to-make “Squarker” lets you know exactly when the points open on 2-stroke magneto engines.
    Photo by Bruce Pierson
  • Detailed diagram of the circuit on the Squarker.
    Illustration by Bruce Pierson
  • The component overlay for the Squarker.
    Illustration by Bruce Pierson
  • A look inside the Squarker, with the battery waiting to be placed in the right portion of the component box.
    Photo by Bruce Pierson
  • The original Squarker is at left; the new and improved Squarker is at right.
    Photo by Bruce Pierson
  • The PCB components.
    Illustration by Bruce Pierson

If you have ever needed to set the ignition timing on a 2-stroke magneto engine, you may have had difficulty knowing exactly when the points open. It’s not something that you can easily measure, because the resistance of the coil in the magneto is quite low and there is very little difference in the resistance across the points when the points are open as compared to when they are closed.

This handy device, known as a “Squarker,” solves that problem, because it is able to detect very slight changes in resistance, down to less than 1 ohm. I constructed my first Squarker around 40 years ago, when I was working as a motorcycle mechanic. I still have this original unit and I have used it from time to time over the years since leaving the motorcycle trade. So, why is it called a Squarker, you ask? Just listen to it in operation and you will have the answer.

Recently, I was working on my chainsaw and I experienced an issue with it, in that it would not start after I had fitted new points. I suspected that the points were not making proper contact when closed, so I dug out my old Squarker to check if this was the case. I hadn’t used it for a long time and it didn’t have a battery in it, so I fitted a new battery and I ascertained that the points were not making proper contact when closed, as I had suspected. A quick file with a points file and resetting the points gap fixed the issue and the saw was running well again.

This started me thinking that the Squarker would make a good project, because it uses readily obtainable components and would be relatively simple to construct while having multiple uses. I opened the old Squarker again and studied the construction. I was not exactly sure how I had constructed this unit, because it had been assembled on four tag strips with point-to-point wiring, which was the standard of the day.

I started by drawing out the components as they were laid out. This proved rather difficult because of the way the unit was constructed, but with the aid of a small mirror I managed to make a drawing of all the components and how they were connected. At this point, I had to enlist the assistance of my son, who studies physics, to help me re-draw the circuit into a more readable state.

There was also the issue of trying to identify the two transistors that were used in the original circuit, as they appeared to be prehistoric types with no visible identification on them. I established that they were NPN types and I worked out the connections for them. Having the circuit in a more readable state, I established that the two transistors were configured as an astable multivibrator, driving a mini speaker transformer into an 8 ohm speaker.


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