C15 Ignition Timing

There are two types of engine on the C15, the first being the distributor model which was manufactured up until 1965 and then came the side points model. Although they look different, they are basically the same in action and setting up is the same in practice. Using these two types of engine there are Standard Road configuration using battery and coil ignition and Competition Models that use a Energy Transfer System instead of a battery.

1) Set the points gap (All Models)

The points gap should be 0.015" (0.38mm) and you will find that you will have a feeler gauge of this size. If you have not come across a feeler gauge before, it is a set of metal strips each one a specific thickness, which is marked by etching on the blade.

a) Remove the spark plug.
b) Remove the Points Cover (A)
c) Put the bike in top gear, then by turning the rear wheel rotate the engine until the cam (E) lifts the points follower and opens the points to their maximum gap.
d) Check the points faces are flat and clean. If they are not, they should be smoothed off with a fine piece of emery paper.
e) Now check the gap by sliding the feeler in between the points (B). It should slide between the points and you should be able to feel some resistance as the feeler touches the points.
f) If the gap is too large or too small, slacken screw (D) and adjust the gap. Tighten screw and retest.

2) Set the Ignition Timing.

(If you are timing a Competition Model C15T or C15S go to to section 4)

If the points gap is not correct, you are wasting your time going any further.

a) Find a pencil or similar size bit of wood that will pass through the spark plug hole.
b) Now rotate the engine until it the piston reaches the top of it's stroke, This is called top-dead-centre (TDC). You find this by placing the pencil in the plug hole in a vertical position and allow it to rise as the piston comes up. When it stops you have TDC. Make a mark on the bit of wood level with the top of the plug hole.

On a four-stroke engine, TDC occurs twice, once when the valves are open and once when they are closed, the later is called the compression stroke. We need to set the timing on the compression stroke. Top find the correct stroke, either turn the engine over with the spark plug in place until you feel the resistance as it compresses the air or remove the valve caps and check that both valves are up (closed) and their rockers are free at TDC.

c) Make another mark on your bit of wood 1/32" (0.8mm) above the other TDC mark. Rotate the engine backward a bit until this mark is below the plug hole, now gently rotate the engine forwards until the mark is level. At this point the points should just be opening.

The best way to see when the points open is to remove the wire from the distributor at C and attach a battery and bulb, earthing the other end of the circuit to the engine. When the points are closed the light will be on and as they open it will go out. This can be done with the side points by disconnecting the bullet coupling in the black and white wire as it comes from the engine points case and attaching the battery and bulb to the wire coming from the engine.

3) Adjusting the timing (Road Models)

Here the two models employ different methods which I will describe separately.

Distributor Model

To adjust the timing on this model we simply turn the distributor body. To do this we must first loosen the clamping screw.

a) Remove the timing side outer engine cover.
b) Set the piston in the correct position
c) Slacken the locking screw (E)
d) Rotate the body anti-clockwise until the light comes on
e) Rotate the body back until the light just goes out and tighten screw (E)

Side Points Model

To adjust the timing on this model we simply turn the contact breaker back plate.

a) Remove the timing side points cover.
b) Set the piston in the correct position.
c) Slacken the two pillar bolts.
d) Rotate the points back plate anti-clockwise until the light comes on.
e) Rotate the points back plate back until the light just goes out and tighten pillar bolts.

4) Set the Ignition Timing for Competition Models only (C15T & C15S)

These models use an Energy Transfer System and must be set-up accurately as follows.

This applies only to Earlier models fitted with contact breaker units having a 15 degree advance.

Set the contact breaker to .015 in. Bring the piston to the top of the bore on the compression stroke. Rotate the engine backwards so that the piston descends about 1/2 in. then bring the rotor into the position shown with the rotor magnets equally spaced either side of the coil. In this position the contact breaker points should be just about to open, if necessary, adjust by turning the contact breaker housing.

Later models are fitted with a unit, which is limited to 10 deg. advance. These can be identified by the 10 deg. stamped on auto-advance bob-weight visible just below the contact breaker. On these models the ignition setting is 5 deg. B.T.D.C. for both Standard and Competition models.

Tip

An alternative to using a battery and bulb, it to place a piece of cigarette paper between the points. As you turn the engine and the points begin to open the paper will become free.