Looking at the spark plug
Taking out the plug from a cold engine to look at it; type and gap from the manual. No spark test.
This guidance is general — not checked for any one model. Your bike's exact figures and procedures are in its owner's manual or at an authorised service centre.
When to do it
- With hard starting or misfiring
- At the manual's service interval
What you need
- A plug spanner of the right size (often in the bike's toolkit)
- A new plug of the type in the manual, if replacing
Step by step
- 1
Let the engine cool completely; key off.
- 2
Pull the plug cap off by the cap itself — not by the lead.
- 3
Clear dirt from around the plug first so none falls into the cylinder.
- 4
Keep the spanner square and turn anticlockwise to remove it.
Left, an old corroded plug; right, a new one. Your bike's plug type may differ — see the manual.Photo: A7N8X, CC BY-SA 4.0, via Wikimedia Commons - 5
Look at the tip: light tan-grey is usually fine; black soot, wet, oily or worn electrodes are worth showing a mechanic, or replacing.
Close up: left, a worn and sooted electrode; right, a clean new one.Photo: A7N8X, CC BY-SA 4.0, via Wikimedia Commons - 6
Start it by hand so it cannot cross-thread, then tighten with the spanner as the manual says; push the cap on until it clicks.
Warnings
- Do not test for a spark by holding the plug against the engine and cranking — fuel vapour can ignite and it can shock you.
- Over-tightening can strip the thread in the engine.
Stop and see a mechanic if
- The plug is very tight or the thread binds — do not force it
Sources
- The owner's manual and service booklet: the only reliable source for your bike's figures and procedures.
Last reviewed: 2026-10-25