"Won't Start"

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Once you have removed the engine cover, you should see a flywheel (a big round disk with a lot of fins-the engine-cooling fins sticking up from it). The electronic ignition is a little plastic-enclosed box or disk that's almost touching the flywheel (Fig. 4). If there's corrosion on any of its wire leads or at the point it bolts to the engine, electricity won't flow through the system. And sometimes those parts can get corroded if the machine's been left out in just one good rainstorm.

So pull out the connecting wire ends, and scrape or sand off any corrosion. Then disconnect the two bolts that hold the CDI on, and clean off any crud that's accumulated where the ignition connects to the engine.

The next step, putting the unit back on, is a bit tricky, because you have to make sure it's just the right distance from the flywheel. Your owner's manual will give you the exact specifications for this gap (generally something like .009 to .012 inch), and you can use a feeler gauge to set it. Or you can pull Dennis's shade-tree mechanic's trick of using an ordinary matchbook cover to set the gap. Either way, as you bolt the ignition back on, tap it in the back on alternating sides several times to get the gap set right on both sides, and check it repeatedly with your gauge or matchbook feeler (Fig. 5). You can then test for spark again by holding the unscrewed (but hooked to its wire) spark plug against the side of the engine and spinning the flywheel by hand, A spark should jump across the gap in the plug.

If there's still no spark, replace the electronic ignition, being sure you set the new one in with the appropriate gap. And if after that you still don't have any spark, you've reached a dead end. The problem's beyond amateur status, and it's time to take the machine to a repair shop. At least now you shouldn't be embarrassed: Your mower's not down with a dumbbell's problem.

Magneto Ignition

What about that other ignition system? Most small engines made in the last five years have electronic ignitions, but there are plenty of older machines around with the points-and-condenser setups. If you've got one of those and no spark coming through your (good) spark plug, you need to check the points. This time you've got to pull off the flywheel as well as the engine cover. Getting a flywheel off is tricky: If you try to pry it off or grab it with pliers, you're liable to break off some of those vital cooling fins. You can purchase a handy flywheel remover for the job, or use this Burkholder shop trick. First, remove the nut or star-shaped what-zit (a starter clutch, actually) that helps hold the flywheel on. Then rotate the flywheel by hand until the magnet on it is opposite the spark plug. Now jam as much clothesline or small nylon rope as possible into the spark plug hole (Fig. 6), and then rotate the flywheel counterclockwise until it locks. (What you've just done is cram rope in the cylinder when the piston was down. Then you turned the piston up so it compressed the rope and locked itself and the flywheel in place.) This will keep the flywheel and central shaft from rotating while you undo its bolt.

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