No spark... can I get some help?

[GoFast2014]

Hey guys.
So, I'm working on a 1971 honda trail 70 (CT70KO) and I spent the afternoon cleaning out the carb, the tank and redoing everything I can in the fuel system. I put it all back together and anxiously cranked it. No fire-of course.

I'm not too familiar with points systems, so I'm going to ask for help before I spend money. That's where you come in. I spent a few hours looking at it before finally finding out that it's got a positive body ground configuration. Definitely not something I've worked on before. So I went and found what seems to be an accurate diagram. I've posted it here, if you cant see it well enough the original URL is here: http://ep.yimg.com/ca/I/dratv_2269_123728396

It's got a replacement coil on it, though it has been sitting about 4 years. Here's what I discovered: if you look at the diagram, the coil is fired off the black wire that comes from the ignition switch, and between the two it has a "T" in it that goes to the points and condenser. On my bike that wire shows battery ground all the time the switch is in run position, even when the motor is being turned over slowly. There is a very slight variation in voltage (like, a few tenths of a volt) but for the most part, it's got battery ground on it. If I disconnect the connector that goes to the points/condenser/generator that wire holds steady at battery ground. Again, I'm not familiar with points/condensers, but shouldn't that circuit be switching somehow in order to fire the coil?

How does this system really work, and what voltages should I be expecting to see? My stepdad seems to think the condenser has gone bad, but he's really just winging it. I can't tell you how many times he's just tossed parts and money at something, and that's just not how I operate.

Any tips/tricks/experience you guys could share would really help a lot. Thank you!!

 

[bikebudy]

Just in case, disconnect your kill switch and try it.

many a time I chased my tail over a kill switch being bad.

 

[GoFast2014]

Thank you for the advice, and I thought of that myself as well, but this bike doesn't seem to have a kill switch on it

 

[Inventorpardue]

Your CT70 has AC-powered magneto ignition.

When the engine spins, AC power is generated under the flywheel. The ignition switch kills the engine by grounding out that AC power. If the switch is bad, it can prevent spark.

Spark plugs for the CT are famous for being defective right out of the box. #1 cure is to replace the spark plug, but based on your PM that may not help.

The spark plug boot threads on to the spark plug wire. Often the stranded wires inside the spark plug wire corrode and lose connection. Unscrew the spark plug boot from the wire, then inspect the wire. See clean, shiny wire strands? No? then trim the wire back a little with side cutters until you do. Screw the plug boot back on and test for spark again.

The spark plug boots fail as well, especially the resistor plug boots. Replace the boot if it fails a continuity test, or just replace it anyway. And the spark plug.

The engine MUST be well-grounded to the chassis for the spark system to operate. The engine mounting bosses corrode behind the paint job. Drop the engine and clean the block bosses and frame area. Or run a ground wire to the chassis from the engine block.

The ignition coil needs a solid ground connection where it bolts on. Insure its clean.

The points become worn, pitted, corroded, dirty, fouled, or just collapse due to rubbing block wear. Severe wear includes problems with the points cam. The points are under the flywheel, along with the condenser. Replace the points and set the timing. Replace the condenser, they rarely fail but when they do... it can cause a no-spark situation.

If the wiring is trashed, destroyed, missing, mangled, mashed, broken, corroded, cut, melted, fried, fouled, mis-connected, or in any way wrong, it will need service or repair.

I drew the CT70 K0 wiring diagram in full color some time ago, which includes the ignition switch wiring.

Let me save you some time: use the Honda CT70 manual to service this bike.

Jon

 

[GoFast2014]

Thanks so much for your help. I'll be sure to check the coil wire carefully and run a dedicated ground wire to the motor. As of right now I have already installed a dedicated ground for the coil that uses the mounting screw for connection. I used my meter and found that when I set the leads on the body of the coil and the signal coming from the points I get about a 4 volt surge (AC.) I don't know points well, but I suspect that's a pretty good indication they're working? I was thinking of taking a small tag light bulb or something and putting it in the circuit with the coil to see if the contacts/condenser can support a small load. Is that a good idea/bad idea?

Thanks again for the help you guys. It's very important that I get this bike running by friday afternoon, and unfortunately parts cant be mailed in that quickly. I suspect a bad coil, or a bad wire on the lead. I'll inspect it tomorrow and if it looks ok I'm basically going to go to a sears parts center and try to find some sort of 6 volt magneto style coil that I can put on this thing to at least make it run. I feel like there's got to be a briggs motor or a go kart or something that I could buy a part off of. Amazon has a new coil for 8 dollars with free shipping, but even with rush shipping (50 dollars!!!) it may not be here in time, so I've gotta scrape the bottom of the barrel here.

 

[GoFast2014]

Ok, well I did the test light thing anyway. It didn't flicker, but when the motor was turning it definitely got pretty bright and then died out with the motor. To me I feel like that's an indication that the points are capable of carrying the load

 

[GoFast2014]

Another update (can you tell I'm anxious to get her going?:

I just went to Napa and worked with a guy that helps me out quite a bit, and he was able to come up with a 6 volt coil for a tractor for me. I got that, some new spark plug wire and new ends. Before actually replacing the coil I just wanted to test and see if this would work.

I took this canister type coil and grounded out the - terminal, hooked the + terminal to the wire that signals the coil (from the magneto) and confirmed I had over 6 volts ac to the coil when i kicked it. I hooked up a gap tester to the coil, got nothing. I grabbed onto the tester and slowly turned the motor by hand, I could feel a slight hit, similar to the feeling of the old coil firing on this circuit. I put my voltmeter on AC, peak reading and showed a max of 700 when cranking by hand, an it went "OL" when I kicked it. OL on my meter is over 1000 so I'm assuming it's right in that range since by hand I got 700. These readings are almost exactly the same as what I got on the old coil.

This clearly isn't enough to spark. What am I missing? Two different coils, new plug, wire isn't the issue, ground isn't the issue... what could it be?? The circuit is delivering 6 bolts, and it does light a test light so what could be causing this no spark condition? Just for general info, the secondary winding on the new coil ohmed out at 9.5k and the primary was 1.3

 

[Docdc]

Ok, some things you aren't going to want to hear. These are simply possibilities and in no way am I telling you this IS the problem. You'll have to check each one.

A condenser can be a peculiar thing. On some motors a bad one will just burn up the points. On others it will not allow the engine to run properly. I don't know the Hondas so well but a 70's small Suzuki motor, it will run you nuts. They are cheap. Replace it.

Test the coils individually in the alternator. Each one should be low resistance. Honda doesn't put out a spec. They just say it should read low. Next, test each coil to ground. Resistance should be no continuity (infinite resistance). Anything different, replace the offending coil. You don't have to remove the stator for this. You can go through the plug, you just have to identify the wires.

Measure the coil primary resistance. set the ohm meter to Rx1. Measure between the primary terminal and the mounting flange. There should be continuity measuring 2.1 to 2.3 ohms.

Next measure secondary resistance. Ohm meter set to Rx100 or Rx1000. Unscrew the spark plug cap from the secondary lead. Measure between the secondary lead (spark plug lead) and the mounting flange. There should be continuity measuring 9K to 11K ohms. If the coil doesn't measure properly, replace it.

I hope this helps some. I just don't know how you will get any bad parts quick enough. I wish you the best.

Oh, one more thing. Not often but every once in a while the rotor will go bad. The magnets just get weak from age. There is no other fix than to replace it. I'd do that last.

Doc

 

[Inventorpardue]

x2 what Docdc said.

A 6 Volt tractor coil runs on 6 Volt DC battery power. Even though your bike has a 6 Volt DC battery system, it has AC-powered magneto ignition. Your CT70 cannot make spark using a 6 Volt DC ignition coil from a car, VW, or tractor.

Your CT70 needs a non-integral AC magneto ignition coil.
Not an AC-powered CDI coil.
Not a DC-powered CDI coil.
Not a DC-powered coil.
A small engine coil will not work because those combine the stator winding and secondary coil in one unit. You need an AC magneto coil from a machine with a separate stator, and a condenser to match.

A Honda Cub/Passport with points (1981 and earlier) has such a coil.
A Honda Z50 minitrail with points has an OK coil.

Jon

 

[GoFast2014]

I think I'm just not familiar enough with the magneto system or charging system to follow what you two are saying. You said to check each each coil in the alternator. Does this mean the same coils are being used to charge the bike as the ones used to create the coil signal charge? And if that's the case, I suppose I just need to test them via the two wires that run along with the coil signal?

I assumed the magneto had a set of windings of its own. That's not correct?

And could you guys help me understand what's different about the different kinds of coils? They aren't labeled as ac/dc so is there a way to know? They share similar resistances and the ac signal is technically switching 6v dc according to diagram above, isn't it? so I thought they could be used interchangeably.

This may come as a surprise but I am an experienced ASE master technician, but I've never come across systems like this in current automobiles. I mean, this things 14 years older than I am.

All your help is appreciated, guys. Thank you. I'll just have to order everything and replace it all. The time crunch has been the biggest problem all along. Now that I know it's not going to run this week I can just dump lots of parts into it

 

[Bevelsd]

Have you tried wiring the black wire that comes out of the left side of the engine case directly to the long black wire that goes into the coil?

 

[Inventorpardue]

I think I'm just not familiar enough with the magneto system or charging system to follow what you two are saying. You said to check each each coil in the alternator. Does this mean the same coils are being used to charge the bike as the ones used to create the coil signal charge? And if that's the case, I suppose I just need to test them via the two wires that run along with the coil signal?

I assumed the magneto had a set of windings of its own. That's not correct?

And could you guys help me understand what's different about the different kinds of coils? They aren't labeled as ac/dc so is there a way to know? They share similar resistances and the ac signal is technically switching 6v dc according to diagram above, isn't it? so I thought they could be used interchangeably.

This may come as a surprise but I am an experienced ASE master technician, but I've never come across systems like this in current automobiles. I mean, this things 14 years older than I am.

All your help is appreciated, guys. Thank you. I'll just have to order everything and replace it all. The time crunch has been the biggest problem all along. Now that I know it's not going to run this week I can just dump lots of parts into it

Your CT70 has two separate stator coils under the flywheel. One stator coil powers the ignition coil. This stator coil is wound to generate 20+ Volts AC to power the ignition coil.

A second, electrically separate stator coil with dual outputs, powers the headlight and the rectifier. This stator coil has nothing to do with the spark system.

The ignition coil has a condenser that matches it. The exact microFarad rating of the condenser is dynamically mated to the ignition coil to help prevent sparking at the points, while maximizing spark. The stator coil that powers the ignition coil is part of this tuned system.

The main differences inside the ignition coils: the turns ratio and wire gauges. The primary winding takes in the low Voltage, then induces magnetism into the secondary windings. The primary is a few turns of heavy gauge wire, while the secondary is many turns of small gauge wire, much as gears in a transmission mesh together. The impedance and resistance of the coil windings also play into the game, because the milliAmps of output power vary. It takes more Amps to light a cylinder in a car engine than the tiny fire in a small motorcycle engine... thus a car coil has bigger wires inside.

Consider the turns ratio needed to make a 30,000 Volt spark happen:

Automotive ignition coil: 12 VDC in, 30 kV out... 2,500:1 ratio
Honda CT90 battery coil: 6 VDC in, 30 kV out... 5,000:1 ratio
Honda CT70 magneto coil: 40 VAC in, 30kV out... 750:1 ratio
Honda Spree CDI coil: 200 VAC in, 30 kV out... 150: 1 ratio

Since the automotive coil outputs more milliAmps of high Voltage, it has beefier primary and secondary windings... and requires far more input Amperage in, to push that heftier spark current out.

The resistance of all the primary windings will be very low, however the impedance (resistance to the flow of electricity) is very different. Add to this fact there is a dynamic resonance in the ignition coil and stator winding... the coils are "tuned" to one another to maximize spark output.

The only way I know to tell the difference in coils is to bench test each one using an oscilloscope and a waveform generator. Measuring impedance, reactance, resistance, and calculating the turns ratio is needed. Much easier to keep track of part numbers; bag and tag the parts.

Hope that helps, looks long to me.

Jon

 

[GoFast2014]

It does, thank you.

I'm SHOCKED that this system could put out 40 volts AC. So, when I'm reading 6 volts, that's the problem? It should be 8 times that, correct? To be specific, I tested that with my Fluke 87-V meter on the peak sample setting so I feel like it's pretty accurate.

This bike has never had good power. Years ago there was a little honda 50 that ran laps around me on this thing. We always assumed it was from shotty carb work thanks to the last guy who worked on it-maybe it was actually a weak spark this whole time.

I do appreciate you taking the time to write all that out. I'm the kind of person where I either don't understand something at all because I'm making jumps in information, or I've got it down and can dissect and manipulate the components easily. There's always a light bulb moment when I'm learning something. Trying to do so without seeing the parts and how they interact is what's made this challenge difficult.

So, let me ask you this to finalize my understanding:
The system charges via a dedicated winding, and it stores the energy where? My thought would be in the condenser (capacitor) but they operate as a DC device, don't they? so how does it store energy in this AC circuit? And how does breaking the points contact initiate the spark? Here's my thought, and please correct me if I'm wrong. It seems to me that the circuit is constantly shorted to ground through the points, meaning the coil has no current flowing through it until the points open, the cap begins to charge in order to prevent a spark between contacts, and at that time the coil accepts the ac voltage and fires. I've been told that the system (either cap or coil) charges while the contacts are closed and the opening of the contacts is what actually fires the coil though. I'm just not understanding how that happens if the circuit is grounded via the points before they open.

Either way, it sounds like I have a bad magneto winding, or a bad condenser. I'm going to order a basket of parts from dratv right now

 

[Inventorpardue]

It does, thank you.

I'm SHOCKED that this system could put out 40 volts AC. So, when I'm reading 6 volts, that's the problem? It should be 8 times that, correct? To be specific, I tested that with my Fluke 87-V meter on the peak sample setting so I feel like it's pretty accurate.

This bike has never had good power. Years ago there was a little honda 50 that ran laps around me on this thing. We always assumed it was from shotty carb work thanks to the last guy who worked on it-maybe it was actually a weak spark this whole time.

I do appreciate you taking the time to write all that out. I'm the kind of person where I either don't understand something at all because I'm making jumps in information, or I've got it down and can dissect and manipulate the components easily. There's always a light bulb moment when I'm learning something. Trying to do so without seeing the parts and how they interact is what's made this challenge difficult.

So, let me ask you this to finalize my understanding:
The system charges via a dedicated winding, and it stores the energy where? My thought would be in the condenser (capacitor) but they operate as a DC device, don't they? so how does it store energy in this AC circuit? And how does breaking the points contact initiate the spark? Here's my thought, and please correct me if I'm wrong. It seems to me that the circuit is constantly shorted to ground through the points, meaning the coil has no current flowing through it until the points open, the cap begins to charge in order to prevent a spark between contacts, and at that time the coil accepts the ac voltage and fires. I've been told that the system (either cap or coil) charges while the contacts are closed and the opening of the contacts is what actually fires the coil though. I'm just not understanding how that happens if the circuit is grounded via the points before they open.

Either way, it sounds like I have a bad magneto winding, or a bad condenser. I'm going to order a basket of parts from dratv right now

Your Fluke is indicating the truth: at kickover RPM's, the permanent magnet primary stator coil that powers the ignition is only producing only that low 6 Volts or so. At idle RPM that Voltage is more like 20... and maybe as much as 40 at high revs. I have run disconnected stators on a test fixture, at high speed RPM, and measured Voltages over 100. When connected, the workload creates a Voltage drop. Fact is, the primary generates low AC Voltage at low RPM.

To answer your question, the points remain closed almost all the time. The points are wired across the stator winding, allowing magnetic flux to flow back and forth inside the primary stator winding, while shorting the capacitor.

At the exact moment the points open, the flux in the primary stator coil collapses. Honda timed the passing of the flywheel magnets to maximize on the collapse, sweeping the next magnet pole across the primary just after that points opening occurs. Maximum flux change is what creates maximum spark Voltage in a magneto ignition system.

A hefty, brief Voltage spike on the order of 40 Volts or more is generated in the primary, which is now free to arc across the points. The condenser dutifully absorbs most of that arc, while promoting the Voltage spike to oscillate between the primary and the now-connected ignition coil. The instantaneous burst of spike Voltage suddenly jammed into the primary of the ignition coil, outputs a bright blue high Voltage spark from the secondary winding.

The spark from the ignition coil secondary is brief. The points close and the flux fields build up in the stator primary again. If energy is "stored" anywhere its in the stator winding, and briefly in the condenser.

Hope that helps,

Jon

 

[GoFast2014]

It does, thank you.
So the 6 volts I was seeing may be spec for the low rpm I'm able to kick it to it seems. That being said, maybe my problem isn't behind the flywheel, but may actually be the coil as I had suspected before?

That's interesting that the operating voltage varies so wildly depending on rpm. Is that due to the speed that the magnets sweet across the primary, I wonder.

Either way, I'm just going to have to go the redneck route with it and just toss parts on it till it runs, it seems. I looked at an original manual and they show testing these components to basically involve hooking up a honda specific testing box and pushing a button. Not very helpful in 2014

Thanks for all the help, again. It makes a big difference

 

[b52bombardier1]

Though this bike does not need a battery quite as much as others such as the CT90 and the ST90, it does need at least a jumper wire across the wires where a battery would be installed. If your battery is in a bad enough condition to appear to the remainder of the electrical system as an "open" condition, this would be a problem. To temporarily get around this, jumper the bike battery harness wires together.

Now ..... Please don't get in a big hurry to do what I just suggested unless you like spending money on bike light bulbs. The battery is the voltage regulator on your bike. When you get it started, the first time you rev up the engine, every operating bulb will fry and that headlight ain't cheap. So at least disconnect it and maybe the tail light. The lamps in the speedometer are not so expensive but they will also let out all of their smoke.

Rick

Two CT90 and two ST90 bikes

 

[Inventorpardue]

It does, thank you.
So the 6 volts I was seeing may be spec for the low rpm I'm able to kick it to it seems. That being said, maybe my problem isn't behind the flywheel, but may actually be the coil as I had suspected before?

That's interesting that the operating voltage varies so wildly depending on rpm. Is that due to the speed that the magnets sweet across the primary, I wonder.

Either way, I'm just going to have to go the redneck route with it and just toss parts on it till it runs, it seems. I looked at an original manual and they show testing these components to basically involve hooking up a honda specific testing box and pushing a button. Not very helpful in 2014

Thanks for all the help, again. It makes a big difference

Yes :thumbsup:

 

[GoFast2014]

b52: thanks for your help, but I figured out the black wire situation. Also, I have a new battery installed. my previous problem was the harness had originally been cut before I got to it, so it looked like a small pile of open ended wires when I lifted the seat. The two black wires were curled where the insulation was missing, so I retwisted them and put it to the negative terminal. Not a great idea, it turns out. That's why I thought the bike had a positive ground, because when I was checking for signal to the coil I was getting -5.7 volts. I since read up on the bike and fixed the problem, using a different style quick disconnect on the positive, negative and the twisted together black wires (now my test terminal during this project.)

Inventor: thanks a ton for your help.
I still don't know what's wrong with it, but I can get a coil for 9 bucks from amazon so I'm going to do that before ordering the 200 dollars worth of parts from dratv that are in my shopping cart. As for the voltage being dependent on rpm, I'm gonna make an assumption. I'm actually studying to be an electrical engineer right now, so really focusing in on these things is important. Im sure you've noticed, I'm a man in need of details. So, my thought is this: I suspect the voltage increase is because of the magnetic force, which is converted to "electrical force" or voltage, behind the electrons in the megneto windings when they are shoved through a wire at a speed faster than the typical speed of electricity (relative to the speed of light, which is roughly 340 meters per second.) I'm thinking because the winding is wrapped so many times it's probably forcing the electrons out in a "cluster" if you will. I think I'd demonstrate this idea by putting two juice boxes on their sides and applying light pressure to one vs heavy pressure to the other. You may be getting the same amount of juice, literally, but it's passed in a shorter time so either the voltage, current or both must increase. Does that seem accurate, or is it deeper than that and I missed something?

 

[b52bombardier1]

My suggestion is to get a copy of the wiring diagram and put the wires back to factory condition the way Soichiro Honda intended. Yes, it's tedious work but is what you should do for future ease of maintenance, reliability and when the bike gets sold.

Rick

 

[Havasu Dave]

As for the voltage being dependent on rpm, I'm gonna make an assumption. I'm actually studying to be an electrical engineer right now, so really focusing in on these things is important.

I'll give it a try: (Assuming we all know that frequency is not part of Ohm's Law)

Rate of collapse of the magnetic field around the primary coil affects the output. RPM. (Basic magneto theory)

but

Look at Lenz's Law. (Works off of Faraday's EMF law) Without quoting it, the increased rate of change in a field's polarity directly influences the voltage. (Simplified)

The faster the change in polarity in an EMF environment, the higher the voltage produced.