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Ignition
57
Set points ignition timing in 10 easy stages You need to gather together the following tools to set the timing: Socket wrench with 10mm and 17mm sockets, flywheel puller, flywheel holder, dial guage to establish TDC and firing point, adjustable spanner or open ended spanner to fit the flywheel puller, battery, bulb with two wires, set of feeler guages and screwdriver. Alternatively you can set the timingwith a piston stop/TDC guage and degree disc.
Do not trust any old markings on The mag housing. Only when the same crank, stator, flywheel and mag housing are used in combination can the old marks be re-used. With a dial gage the timing can be set very precisely. The guage is attached in place of the cylinder head. Now turn the flywheel to the point where the dial changes direction. This is Top Dead Centre.
Now mark the position of TDC against the arrow on the mag housing. The amount of ignition timing advance depends on the motor set-up. Details can be found in the individual cylinder descriptions. You can quickly look-up the required cylinder travel in mm in the tables on page 53. Make sure to identify the correct stroke and conrod length when doing so. Most Lambrettas run the standard 58mm stroke with 107mm long conrod. The TV model is an exception to this rule with a 116mm conrod.
When you have marked the TDC position, you must then calculate the ignition advance. In our example engine is an SX200 with an over capacity steel-liner conversion and 72mm piston. It will be run with a TV175 crank with a 60mm stroke. The required ignition advance is 18Âş BTDC (before top dead centre). Expressed in terms of piston travel this equates to 1.84mm BTDC. In order to mark this point on the maghousing, rotate the flywheel anticlockwise...
...when the gauge indicates 1.84mm make a mark on the maghousing lip. The points should begin to open (and fire) at this point. If your motor is a new set-up and you want to experiment with the ignition timing, you can make similar additional marks. These are best made at approx 2-3Âş gap from the first mark so that you can quickly adjust the setting later and do not need to remeasure. You may need to retard the timing (less degrees ignition advance) if the motor suffers 'pinking' under load.
When the marking is done (best made permanant by punching the mark on the mahhousing with a screwdriver) you can proceed with the final setting of the timing. Two things need to be adjusted here: The moment at which the points open and the size of the maximum points gap.
First set the points gap. This should fall in the range 0.35mm to 0.45mm, measured with the feeler guage. When correcting the points gap, the screw on the points should be loosened slightly. The adjustment is carried out via the adjustment screw on the stator through the window in the flywheel. Turn the flywheel until the points gap is at it's maximum. You can establish this point by sight.
Using a 0.4mm feeler guage blade set the points gap to the correct distance. Then tighten down the holding screw again. Now you can set the points opening moment. In order to do this attach the test lamp as follows: Battery negative to the engine casing. The battery positive is connected to one of the bulb connectors. The remaining bulb connector is connected to the green stator wire.
The bulb should now be illuminated. Turn the flywheel towards your firing point markuntil you see the brightness of the bulb change. As you turn the flywheel towards the firing point the bulb shines bright. As the points points open it dims noticably. This is the firing point.
When the firing point is too early (to the left of the maghousing mark), you need to turn the stator to the right and vice versa. It can become a bit frustrating when you have to adjust the stator position several times, but persist as it is very worthwhile doing. When you are satisfied with the firing point, replace dust cover, fan cowl, floor board and any other parts that were removed and enjoy riding with a trouble free ignition.