Motorcycle Repair: sl 125 no spark, voltage reg, initial timing

Question
hi my 1971 sl 125 bike was running good and then just bogged down and died no spark i change coil and points still no sparks i have no batterie but have voltage reg and reg refectofier what is most likely to no give me spark and my wires are good  

Answer
Tom, this bike's ignition was designed to be battery operated. The battery is a reservoir for the charging system and helps keep everything balanced. The charging system puts out much more than 7.5 volts when no battery is in the system and can cause overvoltage to damage other electrical components.

The early 100-125 singles have a one piece head with inadequate cam bearing support. The camshafts get loose in the head and that causes the ignition timing to vary a LOT!
Be sure that the camchain is nice and snug, then turn the engine over and watch the points open. Set them to about .012" at the highest point on the point cam, then check the points so that the just open at the F mark on the flywheel. That will get your initial timing setup, assuming that the cam is not too loose in the head. When the flywheel is on the T mark (top dead center) and the valves are both closed, check the sideplay on the camshaft, by grabbing the end bolt and moving the cam up and down and sideways. If there is more than about .006" play the ignition timing will be very erratic.

When you replaced the points did you remove the point plate to check the mechanical spark advancer? Be sure that it is working properly or that will just add to your difficulties.

A bad condenser will also cause lack of spark. Kicking the engine over, while watching the points will show a LOT of arcing at the points when the condenser is bad. This may be more difficult to see if you don't have a battery in the bike.

Make sure that your rectifier isn't fried from the lack of battery in the system. Checking the diodes with a ohm meter and reversing the leads will show if the diodes are still okay or not. If the rectifier dies, that will block or short out the power from the stator to the rest of the electrical system.

Make sure you have .002" valve clearance at T mark, valves closed, too!

Bill Silver