1. The Basics (Always Check These First):
* Battery: Test the battery voltage. A weak or dead battery won't provide enough power for the ignition system. Even if it *cranks*, it might not have enough juice for the spark. Use a multimeter to check the voltage. It should be around 12.6V when fully charged.
* Battery Connections: Corrosion on the battery terminals can prevent proper current flow. Clean the terminals with a wire brush and baking soda solution. Ensure they are tight.
* Kill Switch: Make absolutely sure the kill switch is in the "RUN" position. This is a common oversight.
* Fuses: Check any relevant fuses in the electrical system. A blown fuse will interrupt the circuit.
2. Ignition System Components:
* Ignition Coil: The coil transforms low voltage from the battery into the high voltage needed for a spark. A faulty coil is a common culprit. Testing requires a multimeter and a bit of knowledge about coil resistance – consult a service manual.
* Ignition Switch: The ignition switch might be faulty and not sending power to the coil. Try bypassing the switch (carefully, and only if you are familiar with electrical systems) to see if that solves the problem. This should only be done as a test and is not a permanent solution.
* CDI Unit (Capacitor Discharge Ignition): This is the "brains" of the ignition system. A faulty CDI unit won't send the signal to fire the coil. These are usually more expensive to replace. Testing requires specialized equipment or a known good CDI for comparison.
* Pick-up Coil (Pulse Generator): This senses the engine's rotation and sends a signal to the CDI unit. A faulty pick-up coil will prevent the CDI from triggering the spark. This requires testing with a multimeter or an oscilloscope.
* Wiring: Check all the wires leading from the ignition switch, to the coil, CDI unit, and pick-up coil for breaks, shorts, or corrosion. A damaged wire can interrupt the circuit.
3. Other Possible Causes (Less Likely but Worth Considering):
* Stator: The stator generates AC power to charge the battery and power some electrical components. A faulty stator can lead to insufficient power for the ignition system. Testing requires a multimeter.
* Grounding Issues: A poor ground connection somewhere in the system can prevent a spark. Clean all grounding points.
Troubleshooting Steps:
1. Start with the basics (battery, connections, kill switch, fuses).
2. Visually inspect all wiring for damage.
3. Use a multimeter to test battery voltage and check the coil and pick-up coil resistance (consult a service manual for the correct values).
4. If you're not comfortable working with electrical systems, take it to a qualified ATV mechanic.
Resources:
* Service Manual: A service manual for your specific 1988 Honda Foreman 350D is invaluable. It will have wiring diagrams, specifications, and troubleshooting guides. You can usually find these online (eBay, Amazon) or through motorcycle parts retailers.
Remember safety first! Disconnect the battery negative terminal before working on the electrical system. If you're not familiar with ATV electrical systems, seeking professional help is always the safest approach.
