So your motorcycle won’t start. Not to worry, let’s cover three basic essential requirements for a motorcycle engine to run. Every time I’m faced with a motorcycle that does not run, I start with these 3 basic checks to gather information and narrow down the problem.

 Spark – and at the right time

The first thing I do on a non-running motorcycle is pull all the spark plug(s). This gives me a chance to inspect the plug(s) and get a better idea of how the engine was running (See this post on reading spark plugs). Also, they need to be pulled in order to perform a compression test that I will cover in the next section. Now, with the plugs pulled, are they dry or wet? Dry indicates no fuel made its way into the combustion chamber, and wet means the fuel has made its way and did not ignite. One note about a wet plug, make sure the plug is not completely soaked, otherwise this indicates a flooded engine.

So what is the basic function of the ignition system? The spark plug must “spark” and ignite the fuel & air mixture at the right time! Don’t assume if you have spark all is good. Many older motorcycle with breaker points can easily get out of time as the points wear. Refer to your service manual as to whether the timing is adjustable. If it is, double check timing.

To check for spark, insert the spark plug into the boot and ground it to the cylinder head. Turn the key to on and kill switch to run. Hit the starter button or kick the kick starter. You should notice a strong fat blue spark.

Another thing to consider is a fouled plug. A plug is considered fouled when the insulator nose on the firing tip becomes contaminated with a foreign material, such as fuel, oil, and/or carbon. This contamination makes it easier for the voltage to travel on the nose and eventually ground out instead of jumping the gap and firing normally. It’s very hard to tell whether a plug is fouled or not, so when in doubt replace them! Both 2 stroke and 4 strokes can foul plugs. I don’t know how many times I thought the problem was more serious than a $2 plug!

 Compression check

With the plug(s) removed, a compression test can easily be performed. Check out this post on which compression gauge I use, and this post on how to perform a compression test.

Keep in mind that you will need at least around 100psi to have an engine run.

 Fuel and air

So if your engine has good spark & enough compression, in theory is should run when a fuel air mix is introduced. At this point you can try spraying fuel down the carb throat and see if the motorcycle will start up. If you are working on a 2 stroke, make sure you use fuel/oil mix to provide lubrication.

If you follow these steps, you should discover why your motorcycle won’t start. Just remember the 3 basics: spark at the right time, compression, & fuel/air mix.