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Author Topic: Testing Your Ignition System  (Read 1789 times)

Offline rsss396

Anyone looking for a great builder I highly recommend the following.
For CP products dealers I would recommend:
Arlan at LED(site sponsor), Pete Schemberger at Hybrid Engineering, Mat Shearer at Shearer Custom Pipes, Dennis Packard at Packard Racing, and Nate McCoy of McCoys Peformance.

Other great builders I also would recommend: Neil Prichard, Jerry Hall, Bubba Ramsey and James Dodge.

Offline rsss396

Testing Your Ignition System
« Reply #1 on: July 30, 2013, 12:06:06 PM »
another testing procedure

[h=2]CDI ignition systems,trouble shooting,how do they work?[/h]                                                                                                                               There appears to be a lot of misunderstanding and confusion about  the capacitor discharge ignition systems used today on most small IC  engines.The reason for the popularity of CDI systems is that they are  easier to miniaturize than the old fashioned but rugged magneto setups  as found for instance on the B&S lawn mowers.They also dispense with  breaker contacts which will wear out,making a maintenance-free ignition  system possible (at least in theory)
  CDI is a successor to the magneto based ignition systems evolved a  century ago by Bosch of Germany  (Their logo still shows a magneto).It  was a self-contained system,no batteries were required and it was used  exclusively until these became common with the advent of electric  starters).Magnetos were big and expensive and lost out to cheaper  battery ignition,but held their own in motorcycles due to good high  speed performance,They were standard in the smaller 2 strokes as  flywheel magnetos/generators until CDI systems became competitive with  the advent of solid state electronics
 In a CDI ignition system,a storage capacitor is charged to a high  voltage (a few hundred volts) by the flywheel charging coil and, at the  proper moment quickly discharged into the primary winding of the  ignition coil,which is actually a stepup pulse-transformer.The secondary  output is a short very high amplitude pulse which fires the spark  plug.All these events take place during each  engine revolution.The  charging coil is usually located inside the flywheel,if there is room  for it, but if the flywheel doubles as a cooling fan it has to be  located outside.The spark timing is controlled by a small  trigger coil  located in close proximity to the flywheel which generates a low voltage  pulse (actually two, a positive and a negative one), as the fly wheel  magnet passes by.The  circuitry in the CDI unit uses this pulse to close  a solid state switch (usually a thyrister) to discharge the storage  capacitor into the ignition coil primary and generate the high-voltage  pulse at the secondary to fire the plug.This capacitor has previously  been charged to a high voltage with the high energy pulse induced in the  charging coil by the flywheel magnets.All these events take place every  revolution.
  Both the pick up coil and the power coil have two wires connected to  them, one side of each goes to ground (usually coded black),they may be  grounded internally in the magneto or connected together and brought out  as a single wire and grounded outside or connected to a ground  connection on the CDI unit.The two live outputs (charger coil output and  trigger) are connected to the CDI unit.They can be identified by  disconnecting them from the CDI and checking the resistance to ground  with an Ohm meter.The trigger coil has low resistance,the charger coil  higher (a few hundred Ohms typically).Both outputs are ac. signals!!,the  charger output typically in the range of 100 V ac. DC measurements of  this signal are MEANINGLESS and deceiving !,all they measure is the  degree of asymmetry of the ac output,not the actual amplitude.Even  simple multimeters have an ac position.The charger output is an  unhealthy signal that could kill you under the right circumstances,sit  on a wet saddle and grab the bare "white lead" for kicks. while riding  around.This is not all that likely of course,but the output of the  charger coil should be treated with respect.
 I have never set eyes on one of  these Chinese 2 stroke engines,so as  far as color coding goes bear with me,I have concluded that the  "tormentor" "white wire"  is connected to the charge coil output and the  "blue wire" is connected to the trigger coil.Shorting either one to  ground will disable the ignition and stop the engine,in the first case  the storage cap does not get charged,in the second it does not get  discharged.Opening up the connections between  these outputs and the CDI  unit accomplishes the same thing,I would prefer shorting to ground  esp., for the low level signal from the trigger output,a long lead would  be connected to the CDI trigger input and a spurious signal could  conceivably blow up the input device.Shorting them to ground does not  hurt anything and is safer.I would use grounding connections going back  to the engine ground and weather proof the switch and I would leave the  output of the charging coil alone.It is probably possible to power other  devices from the output of the charging coil,I think it could power a   sophisticated high voltage low current dc circuit to minimise the drain  on the coil feeding an efficient power convertor to convert this high  voltage (50 V plus) to 12 or 6  volts power at higher currents.  
 Trouble shooting hints.Caution ,if testing for spark ALLWAYS have a  plug connected with the shell grounded,never ever test with an open plug  lead, you may destroy the ignition coil.
  1) Disconnect leads going to kill switch (shorting mode hookup!) and  try starting engine (Figure out how to stop it in case it runs) .
 2)The charge coil and trigger coil are fairly robust devices and not  likely to fail,measure resistance to ground (disconnect from CDI),if  shorted or open circuit,they are defective or leads bad.
  3) Ignition coil,disconnect from CDI if possible,measure resistance to  ground of primary,should be a few ohms,measure secondary resistance to  ground, should be a few thousand ohms.Caution: High resistance may be  due to high resistance HT lead to plug!.Not easy to check unless you can  get at coil output directly.
 4) CDI unit,probably implicated if other tests OK            
Anyone looking for a great builder I highly recommend the following.
For CP products dealers I would recommend:
Arlan at LED(site sponsor), Pete Schemberger at Hybrid Engineering, Mat Shearer at Shearer Custom Pipes, Dennis Packard at Packard Racing, and Nate McCoy of McCoys Peformance.

Other great builders I also would recommend: Neil Prichard, Jerry Hall, Bubba Ramsey and James Dodge.

 

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