Questionmy trail bike won't start.It seems to be in the spark.I put a new spark plug in but it didn't help and when you take the plug out and check the fire,it has a yellow spark not blue.could you steer me in the right direction on where to start to look for the problem? Thanks
AnswerGreg, if you have spark, unless it is erratic due to a malfunctioning CDI box or pulser coil, you probably are looking in the wrong place. Late model bikes with CDI ignitions make a very fast rising, high voltage spark that doesn't look like the old days when you had points and condensers for the ignition controls.
For an engine to run, it has to have spark (at the right time), compression (check those valve clearances.. .002" both valves cold on compression stroke), fuel/air mixture at idle circuits, and part-full throttle metering.
If the bike has good compression, spark, then probably the idle circuits are blocked. With current fuels, the shelf life in the carburetor is about 2 weeks. After that, it separates into gas/alcohol layers, which will usually plug up the idle jet, which is about .015" in diameter. Drain the float bowl, remove the bowl, remove the idle jet, blow it out, hold it up to the light and you should see a small pinhole of light coming through. Once you do, put it back in and then check the choke cable for proper function. Put in a fresh spark plug and it should fire right up....
Bill Silver
