Motorcycle Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
26 Posts
Discussion Starter #1
I purchased a 1972 Honda CB100 for $300 (The engine was locked up, and the kick starter shaft is snapped off the original engine.) and a 1974 XL100 for the engine. I had it running, but then it died when I adjusted the carb. For the life of me I couldn't get it to start. The engine backfired when it stopped, so I thought I screwed up the valves.

Upon further inspection, the valve timing was perfect. I moved on to checking the spark gap and found it to be sparking fine. I don't have a compression gauge. Based on how it feels, it has compression. Finally, I checked the point contact and found the timing severely off. It was firing in the middle of the down stroke! I've not filled it up with gas yet to see if it runs, but I'm betting it will now.

I have a few questions about the CB100:

Would the backfiring have thrown off the point that much? How was it actually RUNNING with the timing screwed up that much?

On another note, does the CB100 have running lights, or do the lights only activate when signaling? I am relighting the whole bike with LEDs since it's cheaper than finding six volt equipment.

Thanks for the help,

Clyde
 

·
Registered
Joined
·
13 Posts
Hey man sorry I can't help you much, I'm in a similar situation.
Are you going to have a 12v system that you just charge from the wall, or how will you mod the stator to charge a 12v system?
 

·
Registered
Joined
·
26 Posts
Discussion Starter #3
I'm not changing to a 12 volt system. I'm simply replacing every single bulb with LEDs since I have LEDs and resistors laying around. $3 worth of LEDs and patience appealed to me more than changing to a 12v system just so I could buy new lights. If I were to change to 12v lighting, I would just buy a DC-DC converter and wire it after the battery. The ignition coil would need changed out, but the stator and battery could remain the same. That's only if the DC-DC converter can put out enough current to supply the bike.

Oh that note, I may convert to 12v later if the LEDs don't work out (So far, they have.) If a DC-DC converter can't put out enough current, I have an extra stator that I'll need to re-wind for that.

If there are running lights on the tail lights, it makes my job a little harder when wiring them. Not all the LEDs would activate at the same time. Only a couple would turn on, then the rest would activate when the brake switch actuates.

Anyone else own a CB100?
 

·
Registered
Joined
·
26 Posts
Discussion Starter #4
Just as an update: gotta pull the engine off. The intake valve is staying open now. It's a shame, really.
 

·
Registered
Joined
·
26 Posts
Discussion Starter #5
Now that I have the cylinder head off, I see that part of the piston is chipped off in the middle. Small flecks of metal nicked the valve seats and edges

Since I have to re-lap the valves, anyone know of a good, cheap valve spring compressor?
 

·
Save them all!
Joined
·
4,278 Posts
I made one out of an old C clamp, but you can get some pretty basic cheap compressors from Harborfreight.com
 

·
Registered
Joined
·
26 Posts
Discussion Starter #7
So, the harbor freight compressor wouldn't fit, so I used a C clamp and some pieces of pipe.

Now that I've lapped the valves, you wouldn't believe the difference in compression it makes. It's amazing. I also cleaned them up and now I just have to reset the timing and attach the carb.

Thanks for the advice. I'll see if it'll run tomorrow.
 

·
Registered
Joined
·
26 Posts
Discussion Starter #8
Bit of a late update: It runs now!

I have to adjust the carb to get it to run smoothly and not lean out or flood, but it was running well! My only concern is that the clutch is acting up. I'd taken off the side panel and I could spin the clutch freely. The plates aren't locked up, but for some reason I can't disengage the clutch even with the lever fully depressed. I think I didn't torque the bolts down enough so there isn't enough force to separate the plates, I'll look into this tomorrow when it isn't so hot.
 

·
Save them all!
Joined
·
4,278 Posts
So, the harbor freight compressor wouldn't fit, so I used a C clamp and some pieces of pipe.

Now that I've lapped the valves, you wouldn't believe the difference in compression it makes. It's amazing. I also cleaned them up and now I just have to reset the timing and attach the carb.

Thanks for the advice. I'll see if it'll run tomorrow.
It makes a huge difference!!
 

·
Registered
Joined
·
26 Posts
Discussion Starter #10
Note to self: Make sure there is gas in the tank before trying to adjust a carburetor.

No amount of kicking will get an engine to go without a healthy dose of aged, liquid, compressed, dinosaur carcass.
 

·
Registered
Joined
·
26 Posts
Discussion Starter #11
Well it runs, but I'm having a weird issue: the turn signals don't turn on if the headlight is on.

I replaced the headlight bulb (25/35W 6V) with a halogen bulb (35/35W 6V). Am I right with my guess that there isn't enough current to trigger the turn signals?

Even if I have the thing connected to a battery charger or running, the lights still have issues. Does anyone have an idea?
 

·
Greatest Member Ever
Joined
·
662 Posts
To check just put the old bulb back in and see if the signals work then. If they do, then the new bulb might be too much of a drain. I'm more inclined to suspect the flasher unit. Especially if all turn signals don't work. Could also be a faulty switch at the handlebar. Easy to determine with a test light.
 

·
Registered
Joined
·
26 Posts
Discussion Starter #13
To clarify: The flasher unit is new, the switch works, and the flashers flash when the headlamp is off. I do not have the original sealed beam (it was broken) and I can't find a source for the sealed beam that's in the US and won't take a month to get here. I think that the battery charger I was using may have shot the battery, so I'm going to check the voltage in the morning.

Thanks for the tip, I'll double check anyway.
 

·
Registered
Joined
·
26 Posts
Discussion Starter #14
It's looking like the battery is bad and won't hold a charge. When I give the engine juice, letting the battery charge a bit, it signals and lights up fine. It's only after letting it sit for a while (off the bike, so it isn't a short), that it discharges.

I'll have to grab another one. Now to fix the clutch.
 

·
Registered
Joined
·
26 Posts
Discussion Starter #16
Yup, it was a new 6v unit. Thankfully, it was just the battery not holding charge, at all. The new one sorted out the electrical issue I was having.

It runs great now, it shifts well, and now I just have to deal with the BMV here. Oh joy.

Thanks for the feedback and suggestions. I appreciate it! This thread can be closed out. :biggrin:
 
1 - 16 of 16 Posts
Top