QuestionHI bill,i have 1974 cb125s that shows spark when u move the
points by hand while grounding the spark plug on metal
but when u check for spark by kick start , there is no spark,i bought this bike with molested wiring harness, i got to this stage by some trial/error but help please, why no spark with kicking,also there is no key so i removed the
connectors and just by passed the ignition,and was able to get to where i am i think i am missing something minor where do i check help thanks bye.
AnswerIn case you don't have the wiring diagram, go here:
http://www.oldmanhonda.com/MC/WiringDiagrams/MCwiring.php#class
and select the one you need.
So, from your brief description, I assume that you do have a charged 6v battery in the system, which allows you to flick the points open and closed to generate a spark at the plug cap.
Your problem could be somewhat esoteric ... or not. You could have a bad condenser, which is allowing you to create a small spark, one at a time, but can't keep up with its normal function when you put rapid inputs (kickstarting) into the mix.
These early bikes had one-piece cylinder heads, which often suffered cam bearing failures, resulting in a loose, wobbling camshaft thrashing around in the head. The point cam is on the end of the camshaft, so whatever slop is in the cam/head interface, the same "extra" motion is being applied at the end of the cam, forcing the points to have a variable gap, while running/cranking. Every bit of sideplay at the end of the camshaft will add/subtract to the point gap, when the engine is being kicked over or running.
Determine how much side play you have with the camshaft, as it turns through a couple of rotations. Probably easiest to do by getting the motor up on compression stroke (valves closed) and then use some pliers to move the end of the point cam sideways, watching for excessive movement. Then, check the point gap to see that it isn't more than about .12-.14" thou. Adjust as necessary, to get it down to this figure. When the points are closed down to these specs, the coil will saturate and should fire each time the points cycle through their open/close phases. If you can watch the points, while kicking, look for heavy arcing. If you see strong arcing, then the condenser lead is loose, disconnected or the condenser is just bad.
If you don't see excessive arcing (be sure that the point faces are nice and clean/shiny), then you could have a weak coil, excessive resistance in the spark plug cap (normally about 5k ohms) or the camshaft is wobbling so badly that the coil is still not saturating sufficiently.
Bill Silver
