"Won't Start"

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Also, don't hold the plug near the spark plug hole, or your spark might ignite gasoline fumes coming out of that opening. By the way, use commonsense precautions the entire time you're working on any engine. No cigarettes or flames of any kind. And always make sure the plug or plug wire is disconnected before you fiddle inside the engine-you want to avoid any possibility of the engine's starting up while you're working on it.

All set? Then pull the crank some, and look to see if a blue or orange spark jumps across the plug's gap. Remember, for any spark test to work, the starter switch has to be set to "start" or "run" (not "off"), and if your machine has a kill switch-the kind of safety lever that automatically shuts off the engine if released-you'll have to hold it back.

(By the way, are you wondering why you're holding the threads against the engine? Because when a spark plug is working properly, current comes in its outside tip and up a metal rod inside the insulating porcelain body. Then it jumps the gap in the inner tip and travels through the threads back to the body of the engine.)

Did you get a spark? Good, then you can put the plug back in place and see if the engine will now start. If not, at least you've learned that your problem is not a lack of electricity, so you can move on to the section "Chasing Fuel."

If you didn't get a spark, replace the old plug with a new one that's the same size and type, and test again. (A local hardware store should have the part.)

Still no spark? Well, you've done the first, easy fix and made sure you've got a working plug. So your problem is probably in the engine's ignition (starter). There are two common ignition systems in use today: electronic (also called CDI) and magneto. We'll start with the electronic one, since it's largely replaced the more troublesome magneto (points-and-condenser) starter.

You are now entering the hitherto forbidden world of engine disassembly.

Electronic Ignition

To get to the CDI, you have to take off the engine cover. You're now entering the hitherto forbidden world of engine disassembly, so here are a couple of cautionary words to help you safely in and out. One: Remember to unhook the spark plug or its wire before you start. Two:Keep track of every part you take off. It's not that hard to take an engine apart; the tough part is putting it all back together.

Many experienced home mechanics thread bolts back on nuts after removing a part or make drawings of what they're disassembling so they can be sure to put the pieces back in the right places and sequence. Those are both good ideas-it's amazing how quickly you can have a world of little homeless metal creatures lying around. Every one of those wayward parts has a purpose and needs to get back to its rightful place. It's like hiking a new trail in the woods. Check over your shoulder every once in a while to see where you've been, and you'll find your way back home just fine.

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