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FAQ – For Motorcycle Owners – DENSO SPARK PLUG

FAQ – For Motorcycle Owners

For Motorcycle Owners

Q1. How compatible are these spark plugs with trial vehicles?

You can expect improved accelerator response and torque.

The “IW series” is suitable for most trial vehicles. Although many of these vehicles use a low thermal value, the thermal value range that IRIDIUM POWER accommodates starts at IW16, so choose one that matches the type of riding you do. You can expect improved accelerator response and torque, thanks to IRIDIUM POWER’s superior ignitability. Recently, with the reduction of installation space in trial vehicles, there is increasing demand for miniature plugs. If this is your case, please try our IK type. However, the gap between the spark plug cable and the insulator will require waterproofing.

Q2. What is the lifespan of iridium spark plugs when used in a two-stroke cycle?

Guideline: Replace after 3000 to 5000 km

Compared with four-stroke, a two-stroke cycle causes greater electrode wear. With the amount of wear estimated to be 1.5 to 2 times the amount in a four-stroke engine, the lifespan of a spark plug in a two-stroke engine is expected to be shortened by about the same amount. Iridium is a high-melting-point electrode material, but it is still subject to spark wear and high-temperature (oxidation) wear. The recommended replacement guideline for iridium spark plugs when used in motorcycles, is 3,000 to 5,000 km (catalog values). (These values were determined with various operating conditions in mind, but this does not include use in racing.) Based on this, it is considered best to replace spark plugs every 3,000 km or so in a two-stroke engine.

Q3. Why is there a terminal at the tip of the spark plug?

This was designed with all types of users in mind.

A plug terminal is a standard feature of IRIDIUM POWER plugs (except for a few types). This is because some types of spark plug cable require a terminal, and DENSO determines its product specifications with all types of users in mind.

Q4. Why does using IRIDIUM POWER in a motorcycle produce a popping sound?

There are two types of possible causes.

There are two types of possible causes for the explosive popping sound upon starting.

  • Afterfiring from the muffler
  • Backfiring due to blowback from the carburetor

If these symptoms were not present in the same vehicle before changing the spark plugs, the reason is likely to be afterfiring.

The causes of afterfiring are:
(1) Unstable combustion due to an abnormally elevated intake pressure (engine brake)
(2) A problem with the ignition device (improper ignition timing, misfiring, etc.)
(3) The air-fuel mixture is too rich (carburetor malfunction, too much choke, etc.)
(4) The valve timing is off

If the problem occurs during starting, it is likely that one of the reasons listed above (2) to (4) is the cause. A specific example for (2) is the ignition timing being off, and specific examples for (3) include a dirty air cleaner and pulling the choke too much.
We often hear that iridium plugs improve ignition so much that users don’t even need to pull the choke to start their engine. If you are pulling the choke all the way, try starting the motor by pulling the choke only halfway and see if this solves the problem.

Q5. How compatible are these spark plugs with old motorcycles?

Because the required voltage for sparking is low, it is a perfect match.

Because IRIDIUM POWER has a low required voltage, it is considered to be ideal for old bikes with weak electrical systems. However, for a vehicle with a noticeably weakened electrical system (ignition system), it may be best to narrow the plug gap by about 0.1 mm.