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Changing the spark plugs

Changing the spark plugs  is an medium difficulty operation and also, you don't need to change them very often - it's a real permissive engine. The best way to do the change is with the tank near empty (tank has to be removed) and with a cold engine.

Getting access to the spark plugs

Put the bike on the central stand (optional). Start by removing the seat and the small side-panels. Remove the fuel tank mounting bolt - don't worry the tank won't fall.

Switch the fuel to off and take the hoses out - fuel hose and vacuum hose (left side, just below the tank). Prepare a surface to place the tank once is removed - some fuel might leak (usually a few drops). Remove the tank slowly by lifting and dragging towards the end of the bike.

Spark plug removal

Once you have the tank out, take a piece of paper and pencil and draw the position of the spark plug caps (the cylinders are numbered 1, 2, 3, 4 starting from the left side, but that won't help much if it's an older bike and the numbers are not visible on the wires, unless you make a draw). Remove the caps& wires and look at the spark plugs from above - you will notice a lot of debris around them - you don't want any debris in your engine. You can remove the debris with compressed air - if you don't have, just use a small hose and blow air around the spark plugs until the debris is gone (use protective glass to protect your eyes). You can as well use a small paintbrush, or a vacuum-cleaner. 

Spark plugs debris
 Honda CB 750 spark plugs
 Click to see the larger image

Using the socket, loosen and remove the spark plugs. After removing each one, it would be a good idea to inspect them.

Inspecting the spark plugs

Spark plugs can indicate any problems with the engine.

  • light gray colored, normal gap - good engine
  • damp oil film - most likely worn piston rings
  • carbon deposits - fuel mixture too rich, clogged air filter

Installing new spark plugs

I'm using NGK DPR8EA-9 - the standard heat range spark plugs (work well, unless is really cold), or you could use Denso Hot U Resistor Plugs X24EPR-U9 . To install the new ones, screw them by hand to make sure they are not cross threaded. Once the gasket touches, tighten a little bit with the wrench. Put the caps back using the paper drawing, the fuel tank hoses, bolt, side panels and seat.


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