Conferences > International Scooterist BBS > Topic #18408
First, you are going to make a piston stopper. Smash the ceramic insulator off spark plug and cut off the terminal tab so all that is left of the spark plug is the metal shell. Next, feed the screw into the remaining spark plug so that the end of the bolt is going toward the tip. Install the locknut and you have a piston stopper. Put the rubber screw cap on the end of the bolt so it doesn’t scratch the piston.
The second thing you are going to do is establish a top dead center (TDC) reference point. Scribe a nice straight line in the case that points to the flywheel. Borrow your Goth sister’s (preferably white) fingernail polish (or yours if you are that kind of guy) and highlight the mark. You can also use paint or Whiteout. This becomes a permanent “pointer.”
Third, thread your newly fashioned piston stopper into the spark plug hole. Turn the flywheel to the right until it stops. At this point the piston is against the stopper. Make a temporary mark on the flywheel where the pointer is pointing. Now turn the flywheel to the left ‘til it stops. Make another mark. Take out the piston stopper.
Fourth, take the protractor and measure the number of degrees between the two marks. Be very careful to make sure the protractor follows the arc of the flywheel (you can use a timing disc, but either will work.) Now divide the total number of degrees between the marks by 2 and mark the exact degree spot in the middle with a scratch in the flywheel. This is your TDC mark. Now look at your manual and, hypothetically let’s say the timing is supposed to be at 5 degrees BTDC. Use the protractor once again to make another mark 5 degrees forward of the TDC mark in the direction that the flywheel turns. A Vespa turns clockwise, so make a mark 5 degrees (on the protractor) to the right of the TDC mark. This is your timing mark (TM). If timed properly, the ignition should fire at the exact moment the pointer and TM align.
On a points ignition, make sure the gap is set correctly. Electronic ignitions have a raised hash mark on the inner case and a corresponding mark on the stator. These should be aligned so that you can initially start the scooter. Hook up the inductive timing light, which requires a 12-volt power source. Those with American P-series scooters can connect the red wire to the battery while the black grounds to the frame. The inductive clip goes over the spark plug wire. On non-battery or 6-volt scooters, you will have to connect the timing light to an outside 12-volt power source like a car battery.
Start the scooter and point the strobe light at the timing marks while pulling the trigger. The marks will be highlighted (when the ignition fires) and will dance around slightly. The ultimate goal is to have the pointer and TM perfectly aligned at time of ignition. With points, you can slightly change the point gap to get it right, although this is not the best way to alter the timing because too small of a gap will burn the points while a large gap will cause points bounce which will result in erratic timing. Electronic ignition is trial and error since there is not a provision for making timing adjustments. You will have to remove the flywheel and adjust the stator, start the scooter, examine with the timing light, and repeat as necessary. Be sure to torque the flywheel each time so you don’t mess up the crankshaft taper.