Full Restoration 1971 CT70 K0

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Paul Quattrocchi

New Member
I need some feedback on my current K0 build. The bike is mostly Honda parts with a few reproduction parts. The engine is K0 with the following upgrades to the engine, CHP Motorsports 88cc upgrade, high flow oil pump and CHP reproduction carb.

I ran the engine 3 or 4 times on a stand using a spare coil. It ran great.

I mated the engine to the bike and it started on the first kick and I ran it for about 3 or 4 minutes. At that time only the horn worked. The headlight low and high did not work (the ignition was in the proper position for lights). I tried starting it after that first run and it wouldn't start.

I pulled the carb to check if anything was clogging the jet. At this point I did not have a fuel filter on the bike. I added fuel filters for both main and reserve. The bike started and I ran it for about 3 minutes. This time the headlight was working. The next thing I knew the headlight wasn't working. The speedometer lights were also not working. I shut it off at the ignition and tried to restart it and it wouldn't start.

I decided to check the points. The gap was fine (all of the electrical parts on this bike are new).

I recharged the battery just to make sure it had full power.

Today I started it again and ran it for about 4 minutes (all of these engine tests are without the chain installed so all inside my garage -- nothing under load). It ran great but again no headlight or speedo lights. The rear brake light works. I checked all of the wiring up front behind the headlight. Everything was connected correctly. Nothing was loose. I tried starting it again and it started. I shut it off and waiting a minute and tried to restart it and it started. Still no headlight or speedo lights.

Can someone give me some ideas on where I should look next? Is it possible that the reproduction rectifier is bad (I can test it out later)? Would a faulty rectifier cause this kind of electrical glitch. I also need to check my Honda branded ignition switch to make sure that it is K0. I might have picked up one for a K1 or newer.

Thanks in advance for any help or guidance you can provide.
 
If this bike was restored with new paint make sure the motor and key switch are all grounded to the frame..paint ,primer, clear coat in the right places could cause a bad ground.? The head light runs off the yellow wire coming out of you stator/magnito,,you can tap off that wire with a volt meter and see if your light coil is putting out any voltage..at least 6 volts and more when you rev it up..after that it passes through the key switch then into the head light bucket,,, if you have volts coming straight from the motor but nothing in the headlight bucket then I would say there’s a problem in your wiring or bad or wrong key switch?
 
Here's an update. I do have the correct Honda brand ignition switch. I checked all of the wiring to see if I could visually see an issue like uncovered bullet fitting possibly touching another wire or metal -- didn't see that. With the current ignition switch I could get rear brake light and rear running light in position two (lights on). With the bike running I could not get the headlight to come on in either position (low or high beam). Note -- At the time of my first post on one instance I started the bike and the headlight worked (low and high beam) but then this current condition continued.

I swapped out the ignition switch and nothing changed. I swapped out the rectifier and nothing changed.

I leaning toward rebuilding the stator. Replacing the current parts which are new with another new stator rebuild kit.

The battery is a new 6v stock CT70 acid battery.

I ran the engine a little while ago. It started fine and ran well for a minute but then started running rough and cut out. After that it wouldn't start. I waited 15 minutes and it still didn't want to start.

Mechanically, I know this engine starts first or second kick. In my opinion it's something electrical but I'm open other opinions which is why I'm here.

Any other feedback would be appreciated. TIA
 
Point gap may be off, did you clean the protective film off them when new with carb spray/brakekleen? Set them to .016 Take a good look at the sparkplug, too rich too lean? Could be a carb and or adjustment issue. Next time you get it running RIDE it for more info on running condition, don't just sit in the garage. Don't use old gas or ethanol gas. E free gas only if possible. Napa has tru fuel. Reproduction stator coils may also have a protective film on them... Use sand paper.
 
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I appreciate your input. I might have 2 issues at the same time. I have a short in one of the wires coming from the battery. When I jiggle those wires with the ignition in position 2 the tail light loses power.

I don't know if that short would make both the headlight and the speedometer lights not work. I think the headlight not working points to an issue with the stator (the lighting coil). If the short around the battery doesn't get the headlight to work then I will rebuild the stator with another set of all new parts.

I was able to put 2 miles on the bike a week ago so it does run. I got it up to 35 mph just to see if it is capable of getting there and it did that fine. No headlight or speedometer lights on that test ride. The gas is new and probably has a small percentage of ethanol.
 
It's important to understand the difference between "short circuit" and "open circuit" .

A short causes fuses to blow or wires to melt .

It sounds like you have an intermittent open, I'd check every single bullet connector on the bike, most will be flat and not shiny, use metal polish to clean them up and once connected and working well, unplug and smear a tiny bit of grease on the bullet to prevent corrosion from returning .

The blown headlight (seal beam typ) is indicative of a failing battery or open circuits causing the alternator to spike it's output .
 
A new aftermarket harness is cheap enough as well. Did you remove the harness out of the frame during the rebuild to inspect it? Mice have a way of chewing on them. An 88cc ''tuned'' should do much better than 35. Point gap is your timing advance.
 
OLD CT said:
A new aftermarket harness is cheap enough as well. Did you remove the harness out of the frame during the rebuild to inspect it? Mice have a way of chewing on them. An 88cc ''tuned'' should do much better than 35. Point gap is your timing advance.
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Yes, this bike didn't have a harness at the start of the rebuild so I purchased a new K0 reproduction harness.
 
I just rebuilt the stator with another set of new parts. I haven't checked the stator that I removed to figure out the issue but the newly rebuilt stator did the trick. Headlights (high and low beam) and the speedometer lights are working now.

I must have made some kind of error when I originally installed the lighting coil on the stator I pulled out.

If it doesn't rain tomorrow I will take it out for a proper test ride.

I appreciate the input that what shared along the way. Thank you
 
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Looks great but I’m 95% sure your cables should go on the inside of the handle bars,,also the clip on the air box is for the rear brake cable to lock into,,,the plug wire routes more down and has a retainer clip that screws to the cylinder.. just FYI..👍
 
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