2004-2009 Honda TRX450R/TRX450ER Service Manual, Page 74Get this manual
MAINTENANCE Replace the plug if the center electrode is rounded as shown'04V5: SPECIFIED SPARK PLUG: Always use the Standard: specified spark plug IFR8H11 (NGK), VK24PRZ11 (DENSO) on this vehicleFor extended high speed riding
ROUNDED ELECTRODE
IFR9H11 (NGK), VK27PRZ11 (DENSO)
After V5: SPECIFIED SPARK PLUG: Always use the Standard: specified spark plug IFR7L11 (NGK), VK22PRZ11 (DENSO) on this vehicleFor extended high speed riding
IFR8H11 (NGK), VK24PRZ11 (DENSO)
To prevent damaging the indium coating of the center electrode, use wire-type feeler gauge to check the spark plug gapDo not adjust the spark plug gap If the gap is out of specification, replace the plug with new one