Setting points-type ignition on an XS650
(1) The cam chain must be correctly tensioned before the ignition timing is
set, see under "Setting the Valves on an XS650" for the instructions on
how to do this.
(2) Put the bike on it's centre-stand, ensure it is in neutral, and remove the spark plugs.
(3) Remove the alternator cover, the round plate with the word "Yamaha" on it on the left hand side of the motor, held on by two Phillips head screws.
(4) Remove the smaller round cover plate at the top of the motor on the left hand side, exposing the points plate.
(5) The upper set of points are for the right cylinder, the lower set for the left cylinder. Do the upper points first.
(6) Using a socket wrench on the nut in the centre of the alternator rotor, turn the engine anti-clockwise, viewed from the left, until the upper points are at their greatest opening.
(7) Then set the points gap to .012" to .016" (12 to 16 thou.) by lightly loosening the screw that holds the points, and rotating the points more open or more closed as required. There is a notch to help you do this by inserting a wide blade screwdriver into the notch and twisting lightly against the point bracket. Use a feeler gauge to verify the gap.
(8) Using alligator clips, attach a 12-volt test light or a multi-meter across the upper set of points, and turn the ignition on. With the points open the light should be on, or the multi-meter should be registering current.
(9) On the edge of the rotor you will see a small etched line; this is the timing mark. On the alternator housing, close to the 6 o’clock position, you will see a number of marks, including the letter F stamped between two lines. The fully retarded ignition timing point is exactly midway between the lines on either side of the letter "F". Rotate the motor anti-clockwise until the timing mark on the rotor is lined up midway between the lines on the alternator housing on either side of the letter "F", and be sure the right hand cylinder is just approaching the top of it's compression stroke. Determine that the right hand cylinder is coming up on the compression stroke and not the exhaust by putting your thumb over the spark plug hole. On the compression stroke you will feel pressure building as the piston comes up.
(10) Stop rotating the motor exactly as the ignition mark on the rotor lines up midway between the two marks on the alternator housing. Do not go past that point and then come back to it, this will put the slack on the wrong side of the cam timing chain and the timing will be off. The motor must be turning clockwise at all times. If you go past, go around two revolutions and try to stop it at the right point this time.
(11) Loosen the two larger screws holding the ignition plate in place, and rotate the entire points plate in the direction of cam rotation, anti-clockwise, until the points
close and the light is off. Then rotate it against the direction of cam rotation, clockwise, until the light or multimeter just comes on. This happens just at the moment the points start to open, and that is when the spark occurs. There is a notch to help you get this position spot-on, using a large bladed screwdriver and twisting to move the plate incrementally. Tighten the plate in this position. If you cannot not bring the firing point retarded enough with the points gap set at the .012" to .016" specification, due to a worn cam or a cheap after-market point set, go back to step (7) and set the gap to .010" (10 thou.). At that gap you will probably be able to get the firing point to where it has to be, and the bike will still run just fine.
(12) Rotate the motor anti-clockwise and check to see that the light just comes on, or multimeter just starts to register current, when the timing mark on the alternator rotor is midway between the marks on either side of the letter "F" on the alternator housing, and the right hand cylinder is on the compression stroke. If the timing mark is outside the lines, either way, when the light comes on, re-adjust the point plate position.
(13) Repeat steps (6) to (12) except now for the lower points and the left hand cylinder. In step (11) just move the lower part of the points plate, which is secured to the entire plate by two smaller screws. Leave the upper points undisturbed.
(14) Replace the covers, and reinstall the spark plugs. Note sparkplugs should be put in finger tight, and then turned by wrench only 1/8 turn more for a used plug, 1/4 turn more for a new plug.