Japanese Four Cylinder Bikes: Setting the Ignition Points Gap

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Setting the ignition timing on Japanese 4-cylinder, 4-stroke motorcycles starts with the contact points. Without the points gap being set, the timing cannot be properly checked or adjusted.

For the home mechanic with a good quality set of tools, setting the contact points is relatively easy and takes about half an hour to do.

As with all mechanical work on a motorcycle, cleanliness is important. The moving parts of the contact points mechanism can be damaged by small particles of dirt and the settings can be erroneous.

Clean With Compressed Air

With the above in mind, the points cover and surrounding case should be cleaned before attempting to check or set the points. In addition, to make it easier to rotate the engine, the spark plugs should be removed; again, with cleanliness in mind, the area around the plugs should be blown with compressed air before removing them.

The first part of the points setting phase is to determine the position of the piston, and also which stroke: inlet, compression, fire or exhaust.

Rotating the engine and observing when the inlet valve opens will determine the position. (If you are unsure of the rotation direction, rotate the engine by putting it into second gear then moving the rear wheel in the normal direction of travel). See note below.

Piston Position

The engine should be rotated until the piston is moving upwards on the compression stroke. (A regular plastic drinking straw placed through the plug hole onto the piston will show the position of the piston). At TDC (top dead center) the drinking straw will momentarily pause before descending; it is in this position when the contact points gap should be checked.

Checking the Points Gap

On some of the Japanese four-cylinder bikes (Suzuki, for example), the contact points operating cam has a line or indentation at its highest point (maximum lift). This mark should be aligned with the center of the points heel when checking the gap. 

To check the points gap, use a feeler gauge of the correct thickness. On most of the Japanese machines, the gap should be 0.35-mm (0.014").  

After setting the gap at TDC and locking the adjusting screw, the engine should be rotated one time and the gap rechecked.

Important Note

As the points gap directly affects the ignition timing; it should be checked after any points gap adjustment (the ignition timing is more important than points gap). Also, the mechanic must be sure that he is measuring between the faces of the contact points and not onto the pip or nub that sometimes forms on the contacts.

A quick check of the ignition timing can be done using a thin piece of paper. The paper should be placed between the faces of the contact points and the crankshaft rotated (see note below). As the crankshaft is being rotated, the mechanic should gently pull on the paper. As the points begin to open (this is the timing point to initiate the plug spark) the paper will pull out or begin to move. The timing marks should now align. Using the Suzuki again as an example, the timing marks can be seen through a small inspection hole in the contact points mounting plate. The timing marks for cylinder's one and four will be marked T1:4, and for cylinder's two and three the marks will be T2:3. 


  • Some Japanese motorcycles (Suzuki, for instance) have a 6 mm bolt locating the points cam onto the end of the crankshaft. Do not rotate the engine by this bolt as they can shear off. If this design is used on your engine, there will also be a large nut to rotate the engine in the same location. Alternatively, the engine can be rotated by the kickstart lever, or by rotating the rear wheel with the bike in gear (2nd).