Bypass CDI for Spark

Bypass CDI for Spark

Has your bike’s ignition not been starting? Do you think the CDI box has gone wrong? 

CDI plays a significant role in starting the bike; if it goes bad, it can produce no spark. This causes the cycle not to start at all.

Although, it is not that easy to detect a faulty CDI because its symptoms can lead to different occurrences. However, if you feel like your CDI has gone bad, let’s find out if you can bypass the CDI for spark since that is essential for ignition or combustion.

What Is a CDI?

CDI is the abbreviation for Capacitor Discharge Ignition and is found in motorbikes, outboard motors, chainsaws, mowers, turbine-powered aircraft, some cars, and small engines.  

It is a kind of automotive electronic ignition that works by storing and releasing an electrical charge. 

How Does a CDI Work?

The way that a CDI works is when it passes an electrical current through the capacitor. This causes an ignition that quickly builds up a charge in it.

This CDI ignition starts by generating a charge in it and storing it up. Once it has all been stored, the charge gets sent to the spark plug, which ignites the engine. 

This is why if your CDI is faulty, it may cause the ignition process to be hindered.

Without a CDI, there are fewer chances of the vehicle starting because it would store no charge, and no spark would occur.

This loss of spark happens when something prevents the voltage within the coil from jumping the electrode gap. For example, this might occur if the spark plug is damaged or fouled, or there are cracks within the distributor cap. 

How Do I Know My CDI Is Not Working?

One way that might indicate a bad CDI is if you’re facing issues with starting the bike, it is running roughly, or the motor is stalled. There are some symptoms of a defective CDI, such as:

  • Backfiring
  • Misfires
  • Dead cylinders
  • Unusual tach behaviour
  • Difficulty starting the vehicle 
  • Any ignition problems
  • Not running smoothly

How Do I Bypass CDI For Spark?

Sometimes, one does not have the time or money to fix the CDI, so many ask if there is an alternative.

It is possible to bypass a CDI for spark. However, it’s more of a temporary fix.

To do this, you would need to:

  • Clean the tank/bank
  • Remove the CDI box or Module
  • Check its resistance specifications
  • Measure the resistance of the primary coil
  • Measure the resistance of the secondary coil
  • Compare their readings

The way you go about these steps is as follows:

Clean The Tank/bank 

Ensure flammable liquids like gasoline have been completely removed from the tank. To do this, you would have to test if the battery is fully charged or not. If not, then replace it immediately.  

Remove The CDI Box Or Module.

The CDI box usually has a bullet connector and two plugs. Once you locate it, remove it, so the electrical terminals are easily accessible to you.

Refer to the service manual and properly follow all the steps to avoid causing any damage.

Additionally, keep in mind that your vehicle should be turned off and cold before you begin with this. It is also recommended to use an ohmmeter to measure the resistance of the CDI.

Check Its Resistance Specifications.

Next up, check the resistance and the technical specifications that should be visible on the coil. Compare these with the normal ones, and the coil is damaged if they don’t meet the specifications.  

Measure The Resistance Of The Primary Coil

The CDI should have three electrical contacts, which can be external or internal. Using the ohmmeter, touch the external one and record its resistance.

Measure The Resistance Of The Secondary Coil

Next up, touch the ohmmeter to one external and one internal contact while connecting the main wire and the distributor of the box. 

Compare Their Readings 

Lastly, you would have to compare their readings, and if they differ from the technical specifications that have been established, the CDI must be replaced.


CDI is the heart and brain of an automobile, with its ignition system being the blood and signals. But, just like everything in the world, this also has durability, after which it can go bad. 

A faulty CDI can be very dangerous, so it’s better to get it detected before it worsens. However, there certainly are ways to bypass CDI for spark.

From detecting the point of fault to temporarily fixing it, the whole process is not as hard. 

Warwick Braith

Warwick Braith is a thrill seeker at heart. He loves getting outdoors and testing his limits in the wild. As a blogger for YapQ, Warwick provides readers with insights and tips on how to get the most out of their outdoor experiences. Whether it's hiking, camping, or simply exploring nature, Warwick knows how to make the most of it.

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