2000 Beta rev3 Ignition issue

[trialmarc]

The bike does not start. There was no visible spark from the spark plug, but spark plug itself was fine when we spark tested with another Beta. So, I pulled out the ignition coil and tested for continuity, I have attached the picture labeling the terminals. Here is what I found

 

• When cranked and the voltage between 1 and 2 reads between 10v to 14v, so the stator seems working
• When tested for resistance, with 2 (ground) disconnected, the resistance reads zero for the following
  • terminals 3 and 4
  • terminals 3 and 5
  • terminals 4 and 5
• Between any of (3, 4, 5) and 6 at the spark plug end the resistance is 1k

So, is the ignition coil defective?

Thanks much in advance!

Edited September 12, 2017 by trialmarc

[2stroke4stroke]

The 200 system is much more reliable than that on the larger models.  After 12 years the trigger coils on mine needed to be replaced.  There are a couple of places in UK that can do this - worth investigating if this is the problem.

Post edit - somehow I mistakenly read that yours was a 200 but the above may apply in any case.  

Edited September 12, 2017 by 2stroke4stroke

[naichuff]

I run a 200 REV 3 and had the stater repaired  The last time it had to have the triggers replaced The older (2000- 2002) have two triggers and have six coils These also can fail I would check there readings also

[trialmarc]

Thanks for the responses @2stroke4stroke @naichuff

BTW, could someone tell me what is a trigger and where is it located?

@naichuff when you say six coils, do you mean six units of what i show in the picture are on the bike? I don't see anything else connecting to spark plug.

Cheers

[lopez]

I think he means the coil windings on the stator - if you had six coils on a trials bike you'd have you hang them off the handlebars or something!

[naichuff]

Hi The stator has 6 coils mounted on it and two trigger units ( behind the flywheel) This generates the power to the CDI unit mounted behind the steering behind the right hand black cover This is connected with a multi plug The other box in there is the regulator for the fan and light Also check the earth wire (brown cable) in there 

[trialmarc]

Update: The ignition coil was bad. and even after the install of new ignition coil, the bike would not start. As it turns out, spark plug boot had gone bad (open circuit), which is a rare coincidence for sure. I was able to get a friend to hard solder the boot connector inside, and finally the bike starts!! I really appreciate all your help.

[dan williams]

New boots are pretty cheap and just screw into the wire. Just cut the wire ~5mm and screw the new boot on.

The older ignition systems have three types of coils. 4-6 big coils with heavy wire to power the lights/fan ~16-20 volts ac

A coil that provides the power to the CDI. These have smaller wire with more turns to generate ~100-300 volts ac. This charges the capacitor in the CDI (capacitor discharge ignition) and powers the electronics in the CDI. Most modern ones contain a uController. Basically a one chip microprocessor.

The last coil is the trigger coil. This coil is a small coil whose sole job is to send a pulse to the CDI at a certain point in the engine rotation to tell the CDI to dump the charge stored in the capacitor through the ignition coil to make a spark. Some systems used two trigger coils to tell the uController how much advance was needed based on engine speed.

if you look at your flywheel you will see one or two odd magnets that look split. These are the trigger magnets. The trigger coils are oriented in such a way that they don't generate a signal from the magnetic field of the other magnets in the flywheel.

Typically it's the trigger coils that go bad so the CDI charges up but never fires.

On the newer bikes the trigger coils/magnets have been replaced with Hall effect sensors. These live outside the flywheel in that little pod where the cable exits the case. There is a notch in the flywheel that trips the Hall effect sensor to generate the timing pulse. This is the same system used in cars.

OK that's my major geek out for the day.

[trialmarc]

@danwilliams: thank you for the response. I have not explored north of ignition coil (towards stator) but will do.

one question: what is the voltage needed for spark? 300v seems small, hence I am asking. Cheers.

[dan williams]

Yup you are correct. The ignition coil is basically an autotransformer that steps that 200-300V up to tens of thousands of volts.

The old point systems had primary voltages that were somewhat lower. Basically running a current through the primary side of the ignition coil and setting up a magnetic field that would collapse when the points open. The collapse would develop the secondary voltage for the spark.

Instead of running a constant current through the ignition coil CDI systems store the charge on a capacitor. On the Beta CDI  I disassembled it was a 400V polystyrene cap. When the timing pulse is given the energy in the cap is dumped into the coil through an SCR or Triac which is a high current latching electric switch. So through the rotation of the cycle the capacitor gets charged, the trigger pulse fires the SCR which dumps current into the ignition coil building a magnetic field and generating the high voltage for the spark. The advantage over points is you can control the ignition curve very precisely and since you are able to generate a spark on the rising edge of the building magnetic field you can sustain spark on the falling edge giving a longer duration spark.

[trialmarc]

On 9/24/2017 at 8:15 PM, dan williams said:

The ignition coil is basically an autotransformer that steps that 200-300V up to tens of thousands of volts.

I am assuming that the capacitor is being charged at 300v from the stator/rectifier to ensure quick charge (capacitor charging time varies directly as the input voltage?). When I measured ignition coil primary resistance it was around 0.5 ohm, and the voltage at the output of CDI (I have labeled this as 1 and 2 in the initial post) when hand cranking the kick-starter was between 10-15v which is what capacitor discharges to induction coil primary I am assuming. I did not see 100v or 300v when cranking the kick-starter, which is puzzling to me as the hand crank did produce spark.

On 9/19/2017 at 3:02 PM, dan williams said:

On the newer bikes the trigger coils/magnets have been replaced with Hall effect sensors. These live outside the flywheel in that little pod where the cable exits the case. There is a notch in the flywheel that trips the Hall effect sensor to generate the timing pulse. This is the same system used in cars.

Does the hall sensor trigger happen by a magnet in the notch? it would be interesting for me to know.

Thanks again for your detailed response.

[trialmarc]

After changing the ignition coil bike ran fine for couple weeks and there is no spark again and bike does not run -- I was talking to one of the local dealers and I was asked to make sure there is no bad ground connection.

I plan to verify the continuity of ignition coil primary as well as secondary ground terminal to chassis. What else should I be checking?  I would appreciate your insights into this. Thanks much.