1970 honda trail 70 will not start--help

#1
hey Honda trail guys I have a 70 ct trail 70 4 speed that was starting on the 1st kick when I got it , now no start, pulled plug , gets spark some times, getting fuel, any ideas ???
 

MikeBear

Active Member
#5
"getting spark sometimes"

Do you mean that one time you'll kick it over and it has spark, then next time it doesnt?
My Suzuki RV-90 did this when I first bought it, and it turned out to be a sheared flywheel key. The flywheel was turning on the shaft to where it shouldn't be, so it wouldn't always have spark when it should have had spark.

I replaced the key, and the bike starts right up every time now.
 
#8
The battery needs to be fully charged for a Honda trail or CT Honda to start. Those need a good power supply for the points and condenser to properly work. Sometimes a weak spark & other times NO spark. A junk or old battery will cause full fielding from the rectifier and cause electrical issues like blowing of fusible links and bulbs in speedo and tail lights. I know it sounds confusing but that's the way they work. To avoid weird electrical issues you can upgrade the original rectifier for a $7 Radio Shack unit and never have starting or charging issues again. A Honda trail series 50cc-110cc can't run without a battery, don't let people tell you otherwise.
 
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#9
The battery needs to be fully charged for a Honda trail or CT Honda to start. Those need a good power supply for the points and condenser to properly work. Sometimes a weak spark & other times NO spark. A junk or old battery will cause full fielding from the rectifier and cause electrical issues like blowing of fusible links and bulbs in speedo and tail lights. I know it sounds confusing but that's the way they work. To avoid weird electrical issues you can upgrade the original rectifier for a $7 Radio Shack unit and never have starting or charging issues again. A Honda trail series 50cc-110cc can't run without a battery, don't let people tell you otherwise.
Respectfully, I disagree, having studied these bikes' electrical systems for years to better design and manufacture a few electrical parts for several Honda models, including some CT's.

All years of the Honda CT70 (Mini Trail 70) from K0-onward, have AC magneto ignition. A stator winding generates AC power for the ignition. The engine will run very well, regardless of whether a battery is present or not. Newest ones have AC-powered CDI, no battery needed to run the engine.

NOTE: a missing or unchargeable battery will allow the battery charging Voltage to rise too high, easily blowing the stop light and dash lamp bulbs.

All years of the Honda CT90 (Trail 90) have battery-powered ignition, and thus this bike requires a charged battery to start and run properly. Ditto for the S90 street bike, just about the same engine/wiring.

All models of Honda CT110 have AC magneto ignition. The engine will run very well, regardless of whether a battery is present or not.

On all CT models, the spark plug boot is prone to failure. Many incorporate a noise-supression resistor inside, which will burn open and fail.

The spark plug wire is comprised of several strands of solid wire. These wires often erode away where the spark plug boot threads into the wire. Unscrew the boot and inspect for blackened or missing strands. Unless you see bright, shiny wire strands, trim a tiny bit off the end of the wire until clean conductors are showing, then thread the spark plug boot back on.

The CT70 points and condenser may need service. Located under the flywheel, the rubbing block on the points will wear down after a while, closing the point gap. In this case, replacing the points will usually restore good spark.

The CT70 ignition coil must be well-grounded to the chassis... likewise the engine must be well-grounded to the chassis. These connections tie the coil ground, coil output, ignition power, and spark plug ground together. The engine mounting bolts and the engine-to-frame bosses will corrode over time and the spark can weaken. Adding a ground wire between frame and engine, or servicing the chassis, will resolve this.

The wiring itself may be corroded, crushed, mangled, disconnected, partly shorted, or just worn out. Same for the brass-plated terminals.

One of my illustrations covers the CT70 K0 ignition switch, which remains similar throughout the model run. The CT70 ignition switch grounds the AC magneto coil power, to kill the engine. The switch can become contaminated with crud after a while. Disconnecting the Black wire from the ignition switch will prove whether you have a bad switch. Note: you cannot kill the engine if the Black wire is disconnected from the ignition switch. This is just for testing.

The $7 "Radio Shack" full-wave rectifier upgrade does not apply to the CT70, only for some models of CT110, and for all models of CT90. There is a way to make a 3 dollar half-wave rectifier for the CT70, similar to the way you make one for a C70 Cub.

Jon
 
#10
My ct70s always ran without a battery. The lights just didn't work as well.

Never had any trouble.

My ct90 will not run without a battery. If it has low charge it will run until you turn on a light it hit the brakes it will shut off
 
#15
Respectfully, I disagree, having studied these bikes' electrical systems for years to better design and manufacture a few electrical parts for several Honda models, including some CT's.

All years of the Honda CT70 (Mini Trail 70) from K0-onward, have AC magneto ignition. A stator winding generates AC power for the ignition. The engine will run very well, regardless of whether a battery is present or not. Newest ones have AC-powered CDI, no battery needed to run the engine.

NOTE: a missing or unchargeable battery will allow the battery charging Voltage to rise too high, easily blowing the stop light and dash lamp bulbs.

All years of the Honda CT90 (Trail 90) have battery-powered ignition, and thus this bike requires a charged battery to start and run properly. Ditto for the S90 street bike, just about the same engine/wiring.

All models of Honda CT110 have AC magneto ignition. The engine will run very well, regardless of whether a battery is present or not.

On all CT models, the spark plug boot is prone to failure. Many incorporate a noise-supression resistor inside, which will burn open and fail.

The spark plug wire is comprised of several strands of solid wire. These wires often erode away where the spark plug boot threads into the wire. Unscrew the boot and inspect for blackened or missing strands. Unless you see bright, shiny wire strands, trim a tiny bit off the end of the wire until clean conductors are showing, then thread the spark plug boot back on.

The CT70 points and condenser may need service. Located under the flywheel, the rubbing block on the points will wear down after a while, closing the point gap. In this case, replacing the points will usually restore good spark.

The CT70 ignition coil must be well-grounded to the chassis... likewise the engine must be well-grounded to the chassis. These connections tie the coil ground, coil output, ignition power, and spark plug ground together. The engine mounting bolts and the engine-to-frame bosses will corrode over time and the spark can weaken. Adding a ground wire between frame and engine, or servicing the chassis, will resolve this.

The wiring itself may be corroded, crushed, mangled, disconnected, partly shorted, or just worn out. Same for the brass-plated terminals.

One of my illustrations covers the CT70 K0 ignition switch, which remains similar throughout the model run. The CT70 ignition switch grounds the AC magneto coil power, to kill the engine. The switch can become contaminated with crud after a while. Disconnecting the Black wire from the ignition switch will prove whether you have a bad switch. Note: you cannot kill the engine if the Black wire is disconnected from the ignition switch. This is just for testing.

The $7 "Radio Shack" full-wave rectifier upgrade does not apply to the CT70, only for some models of CT110, and for all models of CT90. There is a way to make a 3 dollar half-wave rectifier for the CT70, similar to the way you make one for a C70 Cub.

Jon
I just bought a '71 CT70H in pretty nice original shape. The wiring has not been altered at all. My question is: With the bike not running, turning the ignition switch to 'night' should turn on all the lights, correct? The battery checks to 6+v. All the lights work when the engine is running, though they dim at idle. Ignition switch? I haven't taken the time to pull it yet to check.
Thanks in advance for any help, sir!
 
#16
I just bought a '71 CT70H in pretty nice original shape. The wiring has not been altered at all. My question is: With the bike not running, turning the ignition switch to 'night' should turn on all the lights, correct? The battery checks to 6+v. All the lights work when the engine is running, though they dim at idle. Ignition switch? I haven't taken the time to pull it yet to check.
Thanks in advance for any help, sir!
Is it a K0? I had one years ago and I think the the engine had to be running to operate the lights. It needed a battery to operate the ignition, whereas the K1 didnt,If I remember correctly.
 
#17
Is it a K0? I had one years ago and I think the the engine had to be running to operate the lights. It needed a battery to operate the ignition, whereas the K1 didnt,If I remember correctly.
Built 9/71. I just replaced the original speedo cable. It had CT70 K1 stamped on it. Also I must correct myself. I just replaced the burnt out bulbs in the speedo. The neutral safety switch light, and the tail light work in 'day' mode. Just can't see 'em till it's dark.
 

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