Moto Guzzi Le Mans 1000 Ignition Timing

May 15, 2011
Peter Herd

Photo 1: Tools required are screwdriver, feeler gauge, 13mm ratchet spanner, strobe light, multimeter - Peter Herd

Ignition timing is essential to the smooth running, performance and economy of a motorcycle. Adjustment must be done in a methodical and accurate manner.

The Moto Guzzi 1000 ignition system has a pair of contact breakers operating on a pair of coils, which are connected to the spark plugs.

If you also plan to adjust the carburettors, do the ignition timing first.

Marelli contact breaker

The Marelli S311A assembly is fitted between the cylinders. Access is from the right hand side of the bike. It has an automatic mechanical advance but no vacuum-operated advance.

Purpose of the advance mechanism

To achieve the optimum burn point just after top dead centre (TDC), the plug is fired just before TDC. But, the time taken from ignition to burn is constant, regardless of piston speed. Setting the spark to fire at the correct moment for the slow piston movement at starting means it will fire too late at higher piston speeds.

The mechanism rests below 1500 rpm, but then gradually advances, making the spark plug fire earlier. After 4500 rpm, no further advance takes place.

Preparing for points and timing adjustment

There are static and dynamic adjustment methods. Dynamic timing gives better results. However, preparation is the same whatever method is used.

Remove the saddle, then the petrol tank by disconnecting the fuel pipes (close the fuel taps first!) Lift the rear of the tank and pull backwards. Release the two screws to remove the contact-breaker cover. Remove the spark plugs.

Setting the points gap

This is done before timing adjustment. If done afterwards, timing will be incorrect. It might be an idea to simply check the timing before making any adjustments – if its correct, leave everything well alone.

When the points are closed, current through the primary winding of the coil builds a magnetic field. When they open, the current stops and the field collapses. By transformer action a high voltage is induced across the secondary winding. This discharges across the plug electrodes, producing the spark. Setting the contact breaker gap sets the time taken for the coil to build up a magnetic field.

Put the bike in fifth gear. Turn the rear wheel by hand until one of the contact breaker points opens to its widest point. There’s no mark to tell where this – just make your best guess.

From the picture in the owners manual (or using photo 2 here) identify and slacken screws C and D or G and H, depending on which contact breaker you are adjusting.

Use a feeler gauge to set the points gap to 0.40mm (+/- 0.03mm). Tighten the screws.

Move the wheel to open the other set of points and adjust these to the same gap.

Identifying the timing marks

Remove the rubber bung on the right hand side of the crankcase (Photo 3) exposing the flywheel and starter ring-gear teeth.

Turn the wheel in the direction of normal road travel. Look for a short horizontal line scribed to the right of the teeth, marked with a D (Destra is Right in Italian), ignoring other lines. This is the TDC point for the right-hand cylinder. Move the wheel back a little to turn the flywheel downwards. Another line will appear about two teeth along – this is the static mark. Continue turning, and another eight teeth further is the full advance mark. If you are going to use this for dynamic timing, it is useful to highlight it in some way – I used typing correction fluid.

Continue turning to expose the S (Sinistra or Left) cylinder line, and beyond that the static and full advance marks. Ignore any other lines – they have nothing to do with timing.

Static timing

Move to the D mark. This is TDC – but not necessarily on the compression stroke. Look at the higher (closest to the left-hand cylinder) contact breaker set. If the points are on the verge of, or have just opened, it is the compression stroke. Alternatively put your thumb over the spark plug hole and feel the compression as you move the wheel. If you’re still not sure, remove the rocker covers and check the inlet and exhaust valves; they must both be closed for the cylinder in question, determined by a little free play in both rocker arms.

From the TDC mark, move the rear wheel back to line up the flywheel static timing mark with the notch on the side of the hole. Make sure your eye-line is horizontal to the notch and mark. Slacken the two bolts either side of the contact breaker assembly with a 13mm spanner –this is awkward, particularly with the bolt between the cylinders. I use a ratchet spanner, but if available, Guzzi tool 14927000 can be used.

Connect a multi-meter, set on a resistance range, across the points. Twist the contact breaker body slightly one way or the other until the needle moves, indicating the opening/closing point. Tighten the two bolts.

Move the flywheel to the S (Sinistra) mark, again checking for compression, this time on the left hand cylinder. As before, move the flywheel down a little to line up the static mark with the notch on the inspection hole.

The left-hand cylinder points are mounted on a plate, secured by two screws. Irritatingly, they are not indicated by letters in the diagram, but are fairly obvious; you should be able to see the slotted holes of the plate under the screw heads.

Set up the meter across the points and move the plate to set the open/close point. A notch near the left-hand screw, into which a screwdriver can be placed, assists movement.

If there is not enough travel to allow you to set the break point exactly, you can strip out the plate and elongate the slots. Alternatively reset the gap slightly outside the specified measurement.

Refit the cap, fuel tank and seat and return the gearbox to neutral. Check the spark plug type and gap – specified is a Bosch W5 DC with a gap of 0.6mm. An NGK equivalent is a BP7ES.

Dynamic timing

If you have some spare fuel tubing, place the tank back-to-front across the area usually taken by the saddle. Block and strap it in place and connect the fuel supply with the longer tubing. If no tubing is available, refit the tank in its correct position but raise the rear to the extent allowed by the existing fuel lines by resting it on a wood block.

Slacken the two contact breaker bolts as described in the Static Timing section. Connect the timing (strobe) light to the right hand cylinder. Ensuring the gearbox is in neutral, start the engine and bring the revs up to 4500 rpm. Shine the light in the inspection hole and twist the body of the contact breaker assembly so that the full advance mark lines up with the notch, keeping your eye-line horizontal. Tighten the bolts, being careful not to burn yourself on the hot engine.

Repeat the process on the left cylinder, this time moving the contact breakers mounted on the adjustable plate as described in Static timing.

The static timing mark will now appear to be incorrect, but don’t worry about it.

Refit the cap, fuel tank and seat.