1963 Honda C102 no spark

My friend has a c100 and convinced me to buy a c102 that was for sale. I'm mostly familiar with working on 49cc scooters from the 80s until now so no experience with these 60s hondas.

I am not getting spark and can't figure out exactly what the issue is. It has a new battery, new points, new condenser, new spark plug. I checked the ignition coil and it tested right. compression tested around 93. There's no neutral bulb but i got a reading around 3V to the neutral bulb socket when put into neutral.

The ignition had been changed to a toggle switch that has red on one end and all the rest on the other. When it's on i can get the starter solenoid to click from the button, but i haven't messed with the starter motor and nothing happens to it.

It's possible i just dont have the points gapped correctly as I couldn't find anything specific enough to follow to do this in a particular way. I have seen a single spark (or atleast enough current to spark) once or twice but it was very weak and this was before a battery was put on it.

I'm wondering if the selenium rectifier may be bad but don't know how to test it or whether that would impact spark. Are there other electrical components to check? Any information on various forums has been around the c100 which appears to be quite different electrically from the c102 that I got.

Get a test light or ohm meter and check the point gap. They should ground out when closed.

When the points close they have continuity and are grounded.

Old Guy Too Many Bikes said:

Get a test light or ohm meter and check the point gap. They should ground out when closed.

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any other ideas?

Does anybody have any other ideas on this?

Try this. With a continuity tester or test light, make sure that the points ground out when they close and are an open circuit when they are open. Then remove the spark plug and lay it on the head (wire still attached). Get a good 6 volt battery or 6 volt power supply and hook the positive to the hot side of the coil. Ground the neg wire to the engine case. The cold side of the coil should go to the points. Kick the engine over and see if there's a spark at the spark plug gap. If you get no spark, try replacing the condenser.

From your description, I’d investigate that toggle switch by pulling the battery and tracing the wires. Head over to 4-stroke and download the colored wire diagram I shared. There is a specific ignition path that is a part of the original ignition switch.

Few scattered thoughts-

Youre kick starting it, correct? And the clutch isnt slipping, its turning the engine over?

Make sure you're grounding the plug against the engine while watching for spark.

C102 is battery (DC) powered ignition so it needs a totally fully charged 6V battery. Rectifier is just for charging, don't need it for starting. Yeah, C100 is totally different as you've discovered (AC powered ignition).

You can manually open the points with your fingers and you should see a spark when they are manually opened if they were closed, making contact, and getting power.

Make sure you've got power at the ignition coil.

Unscrew the plug cap- make sure you have continuity through the plug cap (from one side to the other). Is the inner core of the plug wire totally rusty and corroded where the cap screwed in? You can cut it back a little to gooder wire if so.

What plug are you running? Is it clean and new?

You can rule out all the wires and switches and just wire directly to the coil for testing, as Old Guy suggested. I don't have a C102 schematic available at the moment but here is the gist of it from a CT90 (also DC ignition) in the diagram below. Points wire attached to the negative "bullet plug" connector of the coil, battery power runs to the power side of the coil. Switch optional (you can just disconnect from the battery if needed when done). Open the points by hand when closed, and you should see a spark.

Thank you all so much for the replies! The info about not needing the rectifier to get spark was helpful, and the direct wiring instructions made sense. When i first got it the kick start wasn't turning the engine (just like you said). After manually turning the crank the kickstart began to turn it over.

Finally had some time to try some things. i tried what old guy said and had no spark. When i got it, I replaced the points and condenser right away (in september), but it seemed like the points weren't grounding out when i checked today, so i put the original points and condenser back on.

i have an inline spark plug tester. I did what old guy said (with direct wiring a battery) and got spark with the original points and condenser. Sometimes it's strong and sometimes it's a bit weak. After verifying i put it back to a normal setup and i was getting spark. Spark seems a bit weak.

I sprayed some starting fluid in and tried a few times but nothing ever started. I currently don't have gas in it. The carb leaks gas when it's open. I will try more to get it fired up when i have time to mess with it.

The battery i was using is a 12V battery that is no good, but still has a 9V reading. My guess is that the crap battery might result in the questionable spark because it doesnt have the current draw needed, just an ok voltage. But i could be wrong. The yuasa 6V battery i bought was too big to fit in the bike so hopefully i can return it. There is a different battery on ebay that says it should fit but i'm uncertain if it will ($40). I'm thinking i should get an actual good battery that fits in it before i spend time trying to get fuel/carb tuning.

I hit up the local thrift shops and purchase those little power supplies. They would be 110 volts ac to 6 or 12 volts dc, usually with an output of 1 to 2 watts (1000 to 2000 ma). They make good power supplies for testing engines when no battery is available and also make good battery chargers.

Old Guy Too Many Bikes said:

I hit up the local thrift shops and purchase those little power supplies. They would be 110 volts ac to 6 or 12 volts dc, usually with an output of 1 to 2 watts (1000 to 2000 ma). They make good power supplies for testing engines when no battery is available and also make good battery chargers.

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i'll check my stash of AC/DC adapters to see if i have a 6V from an old router or something. I have a few 12V smart chargers but thats not a direct DC source.

Oops, I meant to say 1 to 2 amps, not watts.

It's been at least 40 years since I touched a C102, I'd thought it too used the magneto ("energy transfer") ignition but maybe not .

Finding 3VDC in the system means there's a bad battery or poor connection, often the bolts holding the engine to the frame are loose or corroded after 50 years, I generally take them out and wire brush until shiny then use a conductive grease on them before re assembly .

With the key on and the points open you should be seeing 6 VDC at the coil *if* it's a battery powered ignition .

I have no idea where my 1960's Honda shop manuals are but I'm sure it's a simply thing to google '1963 Honda C102 wiring diagram' .

It's easiest to use an .016" drill bit's shank to properly adjust the points, these older magneto powered Motos don't have any advance so the gap controls the timing and is critical to making it run well .

New contact points usually come covered in a corrosion preventative, wipe it off with alcohol and a clean rag or paper towel .

I've received more than a fe new condensers that are no good, an old one that works beats a new one that doesn't any day of the week .

It's also very easy to flood the spark plug so it shorts out and you don't see any spark because it goes directly to ground via the wet insulator .

I hope this is helpful .

Posting pictures of the actual Magneto (AC generator) might help here .