1970 CT70H Manuf. date 6/70 ser# 118130 other shop could not fix

Good afternoon all. I'm waltinbatonrouge. and new to your site...

I received a call from a friend who owns an independent ATV/motorcycle shop about an electrical problem with a trail 70.

The last project, a couple of weeks ago, was resurrecting the electrics on a 1976 CB750K6...it took about 7 hours but it starts, blinks, toots and lights.

Anyway on the lil' honda...apparently another shop threw in the towel after spending a bunch of hours after replacing the points, condenser, spark plug and the coil.
Still no spark..

My background ..did Avionics on F4-J's during the Vietnam war, then other electro-mechanical stuff and I can use a Fluke.

A'hem..So I started with a fair amount of research on your fine site..Thank you very much! And downloaded a Honda FSM and wiring diagram.

I jumpered across the 2 black wires on the battery plug, (no battery installed, apparently ok per the wiring diagram, and research, yes?

i disconnected the bullet splice on the stator plug to check some basics, saw a short to ground and found a bare wire shorted to the frame between the ignition and lighting coil. So i thought voila!

reconnected it turned the key to pos #1 kicked it (with my hand, c'mon its a CT70!)

NNNNNOPE.

ok, so i raised the seat, noticed that the coil was shiny and new, and decided to isolate the coil and start at that end.

trimmed a wee bit off the new hi tension lead for grins.
The NGK plug boot shows 5k ohms, ok
The new, appropriate, ngk spark plug sparks nice and bright when i connect it to one of the leads on the CB750 project bike.

So... i connected a 6v lantern battery to the coil neg to ground side, switched the primary side with 6vdc..

NO SPARK

So...was reading that there were several different coils across the life span of the CT70, ...so
i used a 12v battery, same exercise...nice fat spark. Like a 12v coil would make.

Its my first CT70 (H) so before i pull the engine to check the coil more closely, i though i would approach the collective and see what you thought..

Any tips or tricks...

most appreciatively

walt

Welcome aboard!:wave:

IMHO, you're over-complicating this. Forget what you know about other motorcycle ignition systems. This one more closely resembles what you'd find in a Briggs & Stratton lawnmower engine, pre-CDI era. In terms of ignition, a battery has F/A to do with it, on this model.

Clean the points, verify the gap, new spark plug...then disconnect the stator plug from the wire harness (at the engine), locate the primary coil output (at the engine) and run a jumper from that to the HT (secondary) coil input, bypassing the bikes wiring altogether. If you get spark, then the problem is in the wiring. If not, you've narrowed the list of possibilities to: points, condenser, primary coil, HT coil.

Since you've already tested the HT coil with an ohmmeter, have to guess that the plug cap is okay and in contact with the HT plug lead. Coils don't fail very often. Thus, I'd be a little surprised if there is a problem with the HT coil; it's well-protected. If there is a problem, there's a good chance that it'll be visible. I'd be more interested in primary ignition coil impedance numbers; those don't fail very often either but more often than HT coils. Far more likely to find fouled point contacts (doesn't take much) or a failed condenser (which seems to have become more commonplace in recent years) or something incorrectly assembled (wired).

While the stator plug from the wiring harness at the motor is unplugged and with the spark plug out the bike (just make for easier turning/rolling over). You can take a 12 volt test light hook the alligator clip to the black wire (from stator) and hold the pointed end to the motor case and kick it over. If points, condenser and coils are good you will get test light to flicker.

Check you my cheezy video

https://youtu.be/lOK-5Af74qM

Cheezy? Thats a masterpiece of cinematic art....kinda..

I got sidetracked on the shiny new non sparking 6v, 12v coil issue...will confirm the stator pulse tomorrow and be backatcha...
Walt

Yeah it was very hard to run the camera, hook everything up, kick bike over etc.

Still stuck...
Good afternoon and thanks again for the insight on the lil honda CT70H.
, aw shucks, couldn't leave the "new coil" 6v, 12v? alone so, i pulled the motor and removed the coil..
its a FL601- AC3X-6V coil..more on the coil in a moment

Anyway reinstalled the flywheel, rechecked the point gap at ..014". and watched lukes video..the test light flickers then brightens up as rpms increase... when i spin the stator nut with my electric drill. it outputs up to 8vac at 1500rpms...

However...when i connect the bullet splice from the stator to the primary on the coil and ground the chassis of the coil to the engine block i'm still seeing the 6-8vac on the primary lead of the coil....but no spark with the plug grounded against the block...

the new NGK PLUG sparked using the Honda 750 project bike...
the suppressor resistor is at 5kohms.

thoughts please...I'm close

Kinda tough seeing the HT coil inside the frame. A vintage original should have a blue plastic covering over the windings. At this stage of the process, I'm beginning to wonder if someone swapped-in a CDI coil (oftentimes referred to as a "12v" coil), or if it's just an OER with black insulation. It is important to determine if you have the correct coil for a breaker point ignition, the inductance values are different between them. CDI coils are usually a lot smaller...a good indicator of what you have and how the ignition types differ.

BTW, this is a magneto ignition. Only way to test it is by spinning the flywheel, can't use a battery to supply power...won't work, period.

Good afternoon racerx...I pulled the coil out of the frame..based on your explanation nope its not the original honda coil...
its marked FL601- AC3X-6V heres a pic...

I'm taking a break on it this afternoon and will do some research on the coil itself.

Of course if you have any thoughts..please pass them on...

thanks again walt

True enough, it's a reproduction. That said, it looks like a pretty accurate repop of the original, thus I have to assume that it's correct for breaker point ignition. Maybe test it with an ohmmeter, make sure it's properly grounded to the frame and see if you get spark. If not, time to look at the stator assembly...clean & gap the point contacts, then retest...by spinning the engine over via the kickstarter.

If you have the flywheel removed already, check the wiring going to the points. A detail shot, or two, might be helpful. Give the primary coil a check with the ohmmeter. I doubt you're going to find anything wrong with either coil. These look way too clean, and they rarely ever fail. You're quickly running out of items to check. That means you should have it sorted before long.

Is it possible to have the primary and lighting coils swapped. I think the lighting coil is usually fatter than the primary. AND the primary is the bottom coil. Can't quite tell in your pic.

thanks for the assist, ..I did check the resistance read 2x on the 2 coils when i had them apart, reading per the factory book, they check within spec,....and will doublecheck point/gap etc in am...i torqued the flywheel to 27ftlbs and can roll the engine around very quickly with my electric drill with plug out to check spark..

I bolted the coil ground directly to the engine block.

Will try spark on coil tomorrow independent of the stator using 6v battery. attached are several pics

i completely removed the stator unit from the backing plate when i found the short between the coils..had some pics from that..(repaired short and covered with piece of sleeve..hmmm,actually now that i look at the pic, the short came from someone routing the connecting wire AROUND the outside of the condenser, and being rubbed through by the flywheel, will fix that tomorrow. ) .

have the engine mounted on shops fixture.

the condenser was replaced with a mitsubishi oem from Honda...apparently his touch was a little rough as he broke off one of the tabs..I checked the condenser electrically with my DMM (ohms then volts ) and resoldered the 3 leads..(the old condenser was in the box of parts and also checked ok)

Hi Kirrbby! swapping the coils..ummm worth a shot, but the wiring only allows them to fit one way. (note the lead to the condenser on the bottom coil)
more tomorrow..thanks again...walt

What kirrbby was saying is that a previous owner/mechanic might have mistakenly assembled the stator with the lighting coil inadvertently swapped for the ignition primary. With hacked & repaired leads, it can happen.

Sounds to me like you've found and corrected the real problem.

Here's a pic of a correctly assembled & wired 3-speed stator assembly.
.

nothings out of the realm of possibility ..looked it over this am..because of the orientation of the leads coming from the top coil and the single lead from the lower coil to the condenser..i'm thinking its ok..

so i rechecked wiring, gap etc. ..and connected the coil, and GOT SPARK! Its a dim little 6v spark but its there, yippppeeee!

Only concern is that when checking gap/ timing per the book, I'm not seeing any dimming of the test light anyplace in the rotation when the flywheel rolls around to F, i am using a 12v battery and test light..

thoughts? walt

Make sure your points are clean and making good contact. With the test light connected reach in with a small screw driver and open the points with out grounding it against any metal to see if the light will go dim.

thanks steve..will give it a check...walt

Hi Steve and all! thanks again for your help..this lilhonda is continuing to be a challenge...

1. per page 80 in the factory book, I connected a 12v battery + from the test light to the black points lead and - ground to the frame .rolling the flywheel to the left by hand ..the light dims only very slightly 100 degrees after the F mark.
2. with the points closed and the battery connected as above i reached through the flywheel slot and opened the points with a non metallic screwdriver. No change in intensity of the light.

We rechecked point gap its dead on per the factory book at .014
wet and dry compression is at 150psi

The plug sparks regularly (with 2nd new ngk plug) when you roll the engine over with the kick starter but only pops slightly with a fuel spray.
I hate situations like this...this bike was "rebuild by a shop" but never was able to get it to run...

thoughts again please.

Definitely try fiddling with the points. Starting by setting them to .016 inches...opening them a little more than the Honda spec is often a little better. Check to make sure the SP boot is making good contact with copper wire...spark plug wire. Then, when I'm trying to get a troublesome motor to run, I like to put a little fuel into the spark plug hole...install the plug...put it into 2nd or 3rd gear and push it around in circles, or up and down the driveway. Push starting it will get the whole works spinning and moving and sucking fuel. If you're seeing some spark, even a little, try push starting it.

After you set the points to .016, make sure they're CLEAN. No dust, no dirt, no oil...clean.

I'm surprised if you're able to spin a newly rebuilt motor with a screwgun...counterclockwise, without spinning the flywheel nut off. Unless you're only doing it with the SP removed.

I don't remember if you mentioned it already, but did you verify cam timing?? Circle on the mark at TDC?? Slightly above or below the mark?

Clean tight connections at wire ends... plugs...stator to harness...harness to coil.