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Changing the spark plugs on the Honda CB 750

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.

 


So, what do you think ?