Hi there, I have a 2010 Harley Nightster, and the front cylinder doesn't start. I've changed the sparks plug. I've tried another coil and wires, but still doesn't start. My coil and wires works on ano

Your coil is junk!

A blackened spark plug is a sign of a rich air/fuel ratio or a misfiring plug. You stated that you changed the coil and wires, but did you change the plugs? Spark plugs, even new ones, can, and do, go bad (excessive internal resistance). Make sure that the plugs are also the correct part number for your application, as they could be of the wrong heat range for your bike. I have even heard of guys using a colder plug in the rear cylinder and a hotter plug in the front cylinder because the front cylinder tends to run a little cooler than the rear (increased air flow in the front).

try switching the position of the two coils, the plug wires will unscrew off of the coils and that way you dont have to pull the spark plug wires too,(be sure and change the 2 wire couplers too) if your front cylinder stops firing you know its the coil, if the back cylinder still doesn't fire then your coil is good and you either have a bad #2 spark unit or a bad crank pulse generator.

It sounds like your sensor in the timer cavity on the right side of the engine is bad. Disconnect the blue wire from the coil. Take a spark plug out of the engine, put it back in the spark plug wire, and lay it on the head. Turn the switch on and momentarily touch the blue wire to the coil. When you take the wire off of the coil, you should see a spark at the plug. The purpose of the sensor in the timer cavity is to stop the flow of current in the coil and initiate a spark.

Good Luck
STeve

The first thing I would do is replace the spark plugs again. You can foul a plug and it will cause you more problems than you can ever imagine. I see you have done all the logical things that I would recommend but I did not see you have replaced the plugs after the 200 miles. You would be surprised at how many times a $2.00 part can cause fits beyond belief.