Setting Motorcycle Ignition Timing

Early Japanese 4-cylinder 4-strokes were equipped with contact points. These points systems controlled the ignition timing. One set of points controlled the timing/ignition for cylinders 1 and 4, and the other set for cylinders 2 and 3, in a system known as "wasted spark" ignition (only two ignition coils were used with each firing two cylinders simultaneously, one fire compressed mixture, the other being wasted).

Although setting the points gap and the ignition timing are critical to the performance of these machines, it is a relatively easy job for the home mechanic to do.

The tools required to undertake this job include:

  • Crosshead (Philips) screwdriver
  • Metric feeler gauge
  • Wrench (to turn the crankshaft) - sizes will vary depending on the particular bike (see note below)
  • 12v test light bulb or multi-meter

Spark plug wrench (the plugs must be removed to allow easy crankshaft rotation)

The contact points gap must be set accurately first. Most of these early Japanese machines needed a points gap of 0.35-mm. Turing the crankshaft slowly (ignition off) the points cam lobe should be positioned at its maximum lift against the contact points heel. This job must, of course, be repeated on both sets of points.

Set 1 and 4 First

The number one and number four cylinders' timing should be set first. To find the firing point for these cylinders, the crankshaft should be rotated (see note below) until the piston on number four cylinder is on its compression stroke (a plastic drinking straw placed through the plug hole onto the piston works well).

As the piston nears TDC (top dead center), a set of timing marks on the cam-lobe backplate will come into view through the inspection window.

When the timing marks just start to appear, a 12v test light (or a multi-meter set to 12 volts DC) should be connected across the contact points (one side to ground, one to the hot lead on the other side of the points).

With the light in place, the ignition should be turned on. Further rotation of the crankshaft will bring the points cam lobe into contact with the heel of the points. At the point when the light illuminates, the timing marks should be aligned.

If the timing was out, the timing plate should be loosened, the crankshaft set at the firing point, and the timing plate rotated until the test light is just coming on. Locking the timing plate screws and checking the timing again is essential to the process of tightening the plates screws will slightly alter the timing position.

Timing Cylinders 2 and 3

With the timing set on cylinders one and four, the mechanic should continue rotating the crankshaft until the number three cylinder's piston is approaching TDC. The timing marks for cylinders two and three will now appear in the timing window. The process used for checking/setting the timing on one and four cylinders should now be repeated for cylinders two and three.

Note: Some Japanese motorcycles (Suzuki, for instance) have a 6 mm bolt locating the points cam onto the end of the crankshaft. Do not rotate the engine by this bolt as they can shear off. If this design is used on your engine, there will also be a large nut to rotate the engine in the same location.

Alternatively, the engine can be rotated by the kick start lever, or by rotating the rear wheel.