Checking the ignition timing

The ignition timing must be checked using a strobosopic timing lamp or 'strobe'. Of the two types available, a good quality xenon tube type is preferable to the cheaper neon types, because it will give a more defined image in use, although the latter will usually prove adequate if used in a shaded position. Where a strobe is not available, the timing check must be entrusted to a Yamaha service agent.

Run the engine until it reaches normal operating temperature, then stop it and remove the inspection cover at the left-hand end of the crankshaft. Connect the strobe to the spark plug lead of cylinder No 1 (left-hand cylinder) following the manufacturer's instructions. Note that where a 12 volt supply is required it is preferable to use a separate battery rather than the machine's own, because it is possible that pulses in the electrical system may act as rogue trigger-pulses causing some degree of confusion when the test is made.

It will be noted that the timing plate carries a number of marks. The T mark indicates top dead centre (tdc) and a few degrees from it is the ignition timing mark which takes the form of an inverted U. This indicates the limits of the timing accuracy at the specified idle speed of 1050 + 50 rpm.

Start the engine and set the idle speed to the above figure. It should be noted that a test tachometer is recommended by Yamaha for this purpose, but under normal circumstances the instrument fitted to the machine will give a reasonably accurate reading. Direct the light at the area near the fixed pointer and check that the timing mark 'freezes' with the fixed pointer mark within the limits indicated by the arms of the inverted U.

The timing is not adjustable, so a discrepancy can indicate only two things. It is possible that the fixed pointer has been bent or that the pickup backplate is loose. Alternatively, there is a fault in the TCI unit or the pickup assembly. In either case reference should be made to Chapter 3, Section 8 for more information. All being well, however, the fixed mark should fall between the two arms of the inverted U mark.

0 0

Post a comment