How to Troubleshoot a Yamaha YFM200 With No Spark

by Chris Gilliland

The YFM200, better known as the Moto 4, was the first all-terrain vehicle produced by the Yamaha Motor Corp. The YFM200 was powered by a four-stroke, 196 cc single-cylinder engine that relied on a capacitor discharge ignition system. Although the YFM200 was removed from Yamaha's lineup in 1990, many of these stalwart ATVs are still in use today. Ignition problems, usually in the form of a loss of spark, are common for these older machines and can be caused by any number of malfunctioning components in the ignition system.

Step 1

Remove the seat from the ATV, using the release lever under the rear fender. Connect the battery to an automatic battery charger. Let the battery charge completely. Test the battery's voltage, using a multimeter set to read a 12 volt DC scale. Replace the battery if its voltage is less than 12.1 VDC.

Step 2

Check all of the electrical connections between the battery terminals, the ignition switch, kill switch, CDI unit, ignition coil and spark plug. Reconnect any disconnected terminals or connectors. Replace any components with damaged connectors, as needed.

Step 3

Follow the wiring lead from the top of the left crankcase cover to the four-pin stator wiring connector near the left seat rail. Unplug the connector and insert your multimeter's red probe into the terminal connected to the brown wire. Insert the black probe into the black wire terminal. Set the multimeter to an "R x 10" resistance setting. Ideally, the multimeter should indicate a resistance of 0.4 ohms. If the resistance is greater than 0.4 ohms, replace the ATV's stator, located within the left crankcase cover.

Step 4

Move the meter's red probe to the terminal connected to the white and green wire. Place the black probe in the white and red terminal. The multimeter should display a 196 ohm reading, indicating that the ignition pickup coil is in operating condition. Replace the pickup coil in the left crankcase cover if the resistance reading is not 196 ohms. Plug the four-pin connector into the ATV's wiring harness.

Step 5

Unplug the ignition coil's orange primary wire, located under the gas tank, and the spark plug cable from the spark plug. Connect your multimeter's red probe to the primary wire and hold the black probe against the engine cylinder head or a bolt along the ATV's frame. The multimeter should display a resistance of 0.85 ohms. Move the red probe to the spark plug cable boot. The multimeter should displace a resistance of 5.9K ohms. Replace the ignition coil, if either the primary wire or spark plug cable resistance is not within specification.

Step 6

Unscrew the spark plug from the top of the engine cylinder head, using a spark plug socket and a socket wrench. Check the condition of the electrodes at the tip of the spark plug, as well as the porcelain insulation around the central electrode. Replace the spark plug if the electrodes or insulation are damaged or melted. Check the spark plug gap, the air gap between the outer and central electrodes, using a wire gauge. Adjust the gap, using a gapping tool, if the gap is not within 0.024 to 0.028 inch.

Step 7

Push the spark plug into the spark plug boot, then hold the spark plug electrodes against the engine cylinder. Turn the ignition switch and engine kill switch to the "On" position and turn the engine over, using the pull starter. Watch the spark plug electrodes for a blue spark as the engine turns. Replace the spark plug if a spark does not appear, then turn the engine over again. Replace the CDI unit if a spark still does not appear with a new spark plug. Screw the spark plug into the engine cylinder head and tighten it to 14 foot-pounds, using a torque wrench, if a spark appears.