Maybe Tom will explain it better since he is a mechanic and I am not, but you want to remove the spark plug from the engine. You'll notice on the sides of the spark plug there are flat spots where the spark plug wrench fits against. That's what Tom is referring to as "flats". You hook up the spark plug to the spark plug wire as if the spark plug was still in the engine (but it isn't, it is in your hand). Tom said to place the "flats" (one of them, any one of them) against the engine... he suggested the cooling fins at the top of the engine where you removed the spark plug... that part of the motor. The idea is you want to make an electrical connection between the motor and that part of the spark plug (just as it would when the spark plug is installed in the motor). So that's the ground wire part of the circuit. When you normally run the motor and are putting along and everything is as it should be the engine has a magneto which acts kind of like a generator or alternator in a car engine... that magneto produces an electrical current with every revolution of the motor. The current of electricity goes to the little CDI unit, that black box with the blue wire and the black wire which you have connected to the blue wire and black wire from the engine. The other wire, the big one is connected to the spark plug. The little CDI box condenses the eloectricity coming from the magneto and gives it more power... so that powerful little spark travels through the spark plug wire and every time the engine goes around shoots a spark out the end, called the electrode. That is what we're trying to find out... if the spark is really there and if is is very weak or nice and strong. When the spark plug is in the engine we can't see the electrode since it is down there in the engine ready to set off an explosion once every time the engine goes around. It is like there is a little room and there is both some oxygen and some fuel mixed together... and somebody lights a match... boom! That match is the electrode. Pretty cool whoever thought up the internal combustion engine. Smart! So, we have the spark plug out where we can see what is going on. Tom suggested different ways to have that motor turn over so the engine can make the magneto produce electricity... you could push the bike and walk along a bit (awkward) or use one of Tom's suggestions... but we have to make the engine go around. The outside of the sparkplug is against the engine (grounded) and you are watching to see if there is a spark coming out the electrode. No spark... then no explosion in the cylinder or as we commonly say, "no fire". That then is the problem and we go from there in figuring out why there is no spark... could be the plug, the plug wire, the CDI unit, or the magneto... but if it has a nice spark then we know all of those things are doing what they are supposed to and the problem is not electrical. I was a teacher once upon a time long ago and I'm explaining this as simply as I know how. If it sounds like I'm talking down to you, please forgive me. Because this is cyberspace I don't know if you are fifty years old or eleven, if English is your first language or if your first language is something else. If it is still not clear to you, keep asking. As Tom said... three things are required for the engine to start... fuel, air and fire. We're going to get this baby going!
SB