QuestionQUESTION: Hi, I have a 1965 honda C100 super cub and a 1966 Honda CM91. They both are not getting spark to the spark plugs. I have cleaned the points and made sure the connections are good but I still get nothing. I have even detached the spark plug cap and held the wire directly to the engine block and do not see a spark. Both bikes have had their carbs cleaned and their compression is good. I have spent a lot of time trying to restore and get these bikes running but this problem has me baffled. Do I need new condensers and or coils? How can I check to see if they are good? What am I not doing to help get these bikes firing?
ANSWER: Aaron, You have two bikes with two different ignition systems.
C100 is a magneto ignition. The points should be clean and shiny and set so that they just OPEN at the F mark alignment. If the bike was in a moist climate, you might buy a flywheel puller and remove the rotor, sand the insides of the rotor magnets so they are free of corrosion.
If you spin the engine over and see some arcing at the points the condenser could be bad. Check all of your wiring connections to the coil and check the coil for incoming volts from the magneto. The ignition switch is a GROUND for the ignition, so if you just disconnect the ignition switch, then you will remove any possibility that the switch is to blame for lack of spark.
The CM91 has a battery-powered ignition system. It MUST have a fully-charged 6v battery in the bike to run. Check for 6v at the points when they are open. Again, any excessive arcing means a bad condenser. Hold the plug wire against the motor and flash across the points with a screwdriver. You should get a spark then. If not, then apparently the coil has failed. The spark plug caps should not have any resistors in them.
You can check the primary resistance of the coils with an ohm meter. They should read around 4-5 ohms across the small leads with nothing attached to them.
Wiring diagrams are here:
http://oldmanhonda.com/MC/WiringDiagrams/MCwiring.php
Parts illustrations and part numbers at www.cmsnl.com
Check the valve clearances to ensure that you have good compression when the engines warm up.
Bill Silver
---------- FOLLOW-UP ----------
QUESTION: I followed up by buying a new battery but still no spark so I went through your test procedures and found the coil leads read only 1.4-2.0 ohms. i am looking for a new or used coil at the moment but are there any other problems that could arise if the new coil doen't produce a spark?
As for the honda 50 I cleaned the outer rotor and checked the electric ends but still no spark. I don't see any evidence or arching. should i buy new coils for the alternator or is there something else I should check and look for? Thanks for your insight Bill :)
AnswerCoil is the same as the CT90...
http://shop.ebay.com/items/_W0QQ_nkwZct90Q20coilQQ_armrsZ1QQ_fromZR40QQ_mdoZ
Ask them for an ohms check before you buy, though. That really should be the problem for you. The coils come with a condenser attached, so hopefully those will be okay.
There are two coils for the Cub. One is the lighting coil for the headlight and the other one powers the ignition coil. A bad condenser can short out the sparks, but you should be able to read a small AC voltage from the stator leads coming out to the ignition coil. Make sure that the magneto coil leads are not grounding out anywhere else on their way to the harness. Again, the ignition points contact faces must be clean and shiny with no grit in between them. Gap should work out to be around .012-.016" but they need to open at the F mark alignment. If you over-advance the spark timing, the magneto loses the magnetic signal from the coils. It has to be pretty precise to work properly.
Bill
