Spark Plug Color Charts

Spark Plug Color Charts

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Your motorcycle’s spark plugs can be very useful to diagnose running conditions in your engine. You can use the burn color of your plugs and reference the plug color charts below to determine if your engine is running rich or lean.

  • Good running conditions: If everything is good, the spark plug should have a tan/light brown color.
  • Rich running conditions: If your engine is running too rich, the spark plug will be black and sooty.
  • Lean running conditions: If your engine is running too lean, the spark plug will be white.
  • If the spark plug is black and oily, they are oil fouled.

If your motorcycle does not seem to be running right, take a look at the spark plugs. Whenever you are rejetting or tuning your carburetors, a plug chop can take away a lot of the guess work. A plug chop will tell you how your engine is running a certain throttle positions.

If your spark plugs are white, you’ll want to fix the problem as soon as possible. White plugs are caused by engine overheating. If you run it too long like this, you can ruin your engine and burn holes through the tops of your pistons. Common causes for white spark plugs include:

  • Too hot a heat range spark plug for your engine
  • Low octane fuel
  • Incorrect timing
  • Cooling problems – dirty fins, no/low water for water cooled engine, low engine oil
  • Air/fuel mixture is too lean

The heat range of a spark plug determines when it will fire. If you have a plug that gets too hot and fires are the wrong time consistently, it can burn a hole in the top of your piston. If it’s too cold, the plug will get fouled and stop firing.

Hotter plugs have longer electrodes and cooler plugs have shorter electrodes.

Use this spark plug chart from www.venturers.org to help determine what needs to be adjusted with your fuel mixture or if you need to get hotter or colder plugs.

Spark Plug Color Chart

Oil Fouled

1-Oil Fouled Spark Plug

Too
Cold

5-Too Cold Spark Plug

Good

9-Good Spark Plug

Good

13-Real Good Spark Plug

Best

17-Best Spark Plug

Hot
But OK

21-Kind of Ho tBut OK Spark Plug

Too Hot/Lean Pre-Ignition

25-Too Hot or Lean Pre Ignition Range Spark Plug

Oil Fouled

2-Oil Fouled Spark Plug

Cold/Rich But OK

6-Cold or Rich But OK Spark Plug

Good

10-Good Spark Plug

Best

14-The Best Spark Plug

Good

18-Good Spark Plug

Hot/Lean But OK

22-Hot or Lean But OK? Spark Plug

Too Hot/Lean Pre-Ignition

26-Too Hot or Lean Pre Ignition Range Spark Plug

Carbon Fouled

3-Carbon Fouled Spark Plug

Cold/Rich But OK

7-Cold or Rich But OK Spark Plug

Good

11-Good Spark Plug

Best

15-Best Spark Plug

Good

19-Good Spark Plug

Hot/Lean But OK

23- Hot or Lean but OK? Spark Plug

Too Hot/Lean Pre-Ignition

27-Too Hot or Lean Pre Ignition Range Spark Plug

Too
Cold

4-Too Cold Spark Plug

Cold/Rich But OK

8-Cold or Rich But OK Spark Plug

Good

12-Good Spark Plug

Best

16-Best Spark Plug

Good

20-Good Spark Plug

Hot/Lean But OK

24-Hot or LeanB ut OK? Spark Plug

Too Hot/Lean Pre-Ignition

28-Too Hot o rLean Pre Ignition Range Spark Plug
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