Ignition Diagnosis for 1978-86 CB/CM 400/450 Manual Trans

LongDistanceRider

LongDistanceRider

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Ignition Diagnosis for CB/CM 400/450 and CB450SC manual trans 1978-1986​
These tests are used to check the CDI system. There are no valid tests for the CDI unit at this time so this is an elimination process. If all these tests are good then the CDI is at fault. Before replacing a CDI all these components have to test good.
Use a Multi-Meter, VOM or Volt-Ohm-Meter, with a new battery and set it to measure electrical resistance in Ohms.
Separate the three connectors from the stator to the CDI for the stator tests, use the stator side connections.
The fuel tank has to be removed to test the coil and run/kill switch. The Black w/White wire pigtail is at the CDI.

Coil Test: Primary Side. Measure the resistance between the Yellow and Green wires.
The Yellow and Green wires being measured will be coming out of the spark plug coil.
The resistance should be less than 1 Ohm. Spec is .35 to .55 ohms
Secondary Side: Measure the resistance of the spark plug wires with the plug end caps removed, they unscrew. Insert a probe into each wire. Spec is 7.2K ohms to 8.8K ohms for the stock Honda coil, other coils will have different spec's.
Plug End Caps: Measure the resistance of the plug end caps. Spec is 5K ohms. Replacement part number is NGK XD05F

Stator Tests:
The connectors used are found under the left side cover.

Measure the resistance of the Pink and Green wires in the large 6 position connector
This is the advancer pickup sensor
The resistance should be about 135 Ohms. New Spec 129 Ohms

Measure the resistance between the White and Blue wires in the 2 wire connector.
This is the CDI power source
The resistance should be about 85 Ohms. New Spec 84.2 Ohms

Measure the resistance between the Brown and Light blue wires in the large 6 position connector.
This is the primary pickup coil, the aluminum piece outside the rotor
The resistance should be about 207 ohms. New Spec 203 Ohms

The stator ohm readings listed can exceed the old spec by no more than 1 ohm, more than that will have a negative effect on the timing advance.
The New Spec was obtained by measuring 2 NOS stators, fresh unused old stock early model with the bullet Blue and White wire connectors.

Run/Kill and Ignition switch Tests:
Connect one probe to the Black w/White tracer pigtail wire coming out of the main wiring harness that connects to the CDI unit. Connect the other probe to the negative battery terminal. The results should be:
Ignition switch on, Run/Kill switch in Run position: Infinite Ohms reading meaning an open circuit
Ignition switch on, Run/Kill switch in Off position: Zero ohms or close to that showing the circuit is closed/completed to ground
Ignition switch OFF, Run/Kill in any position: Zero ohms or close to that showing the circuit is closed/completed to ground

Alternator Tests: Use the connector with 3 Yellow wires. Select/connect to one Yellow wire with a probe. Connect the other probe to one of the remaining 2 Yellow wires, resistance should be below 1 ohm. Repeat twice using a different wire each time. If the readings are good then test each of the Yellow wires with one probe connected to ground. There should be an Infinite ohms reading meaning none of the charging coils is shorted to ground.

NOTE 1: Some VOM's are auto-ranging meaning they switch ohm scales as needed and some are range selectable. If you have to select the range be sure to do that matching the expected ohm range.
NOTE 2: Came across a different set of tests from Rex's Speed Shop in the UK
https://www.rexs-speedshop.com/wp-c...250400N-CB250400T-generator-testing-guide.pdf
 
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Since selling the CDIs I have gotten a small rash of people who have cooked CDIs (not mine) via the kits. They want these kits in a desperate attempt to solve their issue thinking they can blindly replace the components on the PCB to figure it out.

Every time this has happened the real issue is the stator and it appears to happen after the bike has warmed up and they buy used CDI units cheap and they still fail after a few miles.

This is clearly a stator issue and it may ohm out good on the bench, but in at least one instance the problem was the ground eyelet on the back of the stator was corroded and barely hanging on. Another time one was redirected to one of the mounting screws and also barely hanging on. My guess is that the bike warms up and also with the vibration is constantly floating the ground and the SCRs are intermittently getting the voltage and pickup being sent to it. It happens so fast and the SCRs cannot take this abuse and fail. In one instance I found that eventually the low RPM coil failed open after multiple attempts to rework the board.

Here's what you should do before you buy replacement CDIs if you are cooking them...

  • Rotate the rotor counter clockwise until you see the magnet. If it is rusty, clean it with 320 and then follow up with 500.
  • Inspect the two screws for the pickup coil. Check continuity for this screw to the green wire coming out of the 6-pin canon plug of the stator.
  • While rotating the rotor make sure that it is not dragging on the pickup coil. If it is then it may cause things to short to ground. If the bike has been dropped or the pickup screws have vibrated loose then it may be dragging. If they're not loose and it's dragging then very carefully bend the bracket back into place.
  • Remove the rotor, get the puller tool from Motion Pro.
  • Remove the stator with a JIS #3 T-Handle. Don't try to be clever with the Vessel screwdrivers. You will likely ruin the screw. A hand impact may work, but if you don't do it right you risk breaking the screw or worse. Instead, LASER Tools sells a JIS T-Handle with replaceable bits; get it from Amazon. Mike Nixon also has a set for sale that is a clone of the original Kowa's.
  • On the backside of the stator is a ground eyelet. Inspect it for damage. Clean this area if it appears corroded. If the crimp is barely hanging on or looks corroded then strip it back until you get non-corroded wire and crimp it correctly. Matt at Vintage Connections has what you need. When replacing the screw use BLUE thread locker. Don't use the hi-temp stuff or you'll never get it out.
  • Check the bottom of the pickup sensor. You'll see a magnet. Make sure it's not dirty. Clean with alcohol.
  • Check 6-pin canon plug. Extract the connectors and make sure they are not corroded. Again, if you must, then peel back until you get good wire and crimp. There's a bit of slack so you can trim a little. If it goes too far you'll have to come up with a solution to that. Sometimes, you can see the wires on the stator side. You can attach a tiny clamp probe to it and then check the continuity out of the 6-pin canon plug by wiggling and twisting the harness. If you have more than 1 ohm resistance on ANY of these wires then it's corroded. If the readings are going wild you either have a dirty connector, probes are not attached securely, or you have junky probes.
  • Now, replace the stator and rotor. Re-attach the CDI. Attach a PVA and crank the bike with killswitch set to OFF or disconnect the 2-pin canon plug coming out of the CDI to ignition coil. If you can't do this because it's kickstart only or your starter is weak, etc. then get a drill with a 17mm socket and spin counter clockwise. You should be getting ~150V-200V out of the blue to ground and white to ground. If you don't then a winding is bad. You should be getting some voltage out of the pickup (brown and light blue) and advance (pink and green) coils. If you don't, again a winding is bad.
  • If all of this is good, back probe to the yellow and green coming out of the 2-pin canon plug of the CDI. Killswitch set to RUN position. Start the bike if possible; if not then spin with the drill. You should be getting about ~1V coming out of the CDI. This will verify, dynamically, that the CDI is discharging the capacitor. There is no other way to test this. There is no wire combination of bench probing to determine this.

If all these checks come back good, your problem is your ignition coil. Very likely you are using an aftermarket one from eBay. I have seen these ohm out at rest at 5 ohms and the meter goes wild. Crappy windings. Check your caps from these coils. With the same crappy coil I found that it had a very sloppy fit. If your coil is under 1 ohm, caps are good, then replace your plugs with genuine (as in bought it from the dealer, DSS or Partzilla) NGK D8EAs. If the bike starts, runs good for 5-10 minutes then shuts off and won't start again for a few minutes and then instantly dies within 30 seconds your coil is tired and toast. Get a Dyna DC11-2 or the GM coil mod.
 
@Maraakate could you toss some links in for the tools you mention, just so we can make sure we're getting the exact tool you're referencing?
 
 
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I've since edited the previous post to add information on the flywheel holder tool, the rotor puller, and the various tools Matt has at Vintage Connections for terminal repair and replacement.
 
Huge thanks to @LongDistanceRider and @Maraakate for this thread! I followed these excellent guidelines to find a bad pickup coil in my stator and a poor quality aftermarket ignition coil.

The nice folks at https://ricksmotorsportelectrics.com/ verified my bad pickup coil and rebuilt it. They turned it around much faster than expected. While waiting for a Dynatek ignition coil to arrive from https://www.hondamaticparts.com/, I tried starting the bike with the newly rebuilt stator and the cheap aftermarket coil I had. No dice. After installing the Dynatek unit, the bike started on the first press of the start button. Wow!

In all this process, I purchased the ESI 640 Peak Voltage Adapter and the Generic Clutch/Flywheel Holder Tool. Both items are very handy. Great referrals, folks. Thanks a ton!

20230801_171701(1600).jpg
 
Pachyderm said:
Huge thanks to @LongDistanceRider and @Maraakate for this thread! I followed these excellent guidelines to find a bad pickup coil in my stator and a poor quality aftermarket ignition coil.

The nice folks at https://ricksmotorsportelectrics.com/ verified my bad pickup coil and rebuilt it. They turned it around much faster than expected. While waiting for a Dynatek ignition coil to arrive from https://www.hondamaticparts.com/, I tried starting the bike with the newly rebuilt stator and the cheap aftermarket coil I had. No dice. After installing the Dynatek unit, the bike started on the first press of the start button. Wow!

In all this process, I purchased the ESI 640 Peak Voltage Adapter and the Generic Clutch/Flywheel Holder Tool. Both items are very handy. Great referrals, folks. Thanks a ton!
Click to expand...

Glad it's running very well now. Those Dyna coils and GM coils really wake it up. The original coils are 40+ years old now. It blew me away that when the weather is good and has been in regular service that it's usually a feather touch of the starter button to get it going. Sorry the turnaround time was a bit longer than expected. It's just a one man operation and I'm not a point where I can stock many of them so right now they are made to order. I appreciate your patience because I know it's important to get it running before the weather changes.
 
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