To repair a Honda ATV engine, first determine what is wrong with the engine; in some cases, engines do not start because the battery may need to be replaced or recharged. Test the battery with a multimeter; if it does not register at least 12 volts, plug it into a charger. If the battery does not charge at all, replace it with a new one. Consult the owner's manual to determine the best way to fix the vehicle.
Troubleshoot the engine for other potential problems, such as clogged air filters or a flooded exhaust line. Air filters in ATVs that travel over very sandy, muddy or dusty terrain should be regularly cleaned so that dirt does not build up and damage the engine. Additionally, a clean air filter allows more air into the engine, which enables it to operate with optimal power and efficiency. If an exhaust pipe becomes submerged in mud or water, tip the vehicle backward to drain it. Change the oil and ensure there is no water inside vulnerable parts, such as the airboot and air filter.
Examine the ATV's spark plugs to see if any of them are corroded or damaged; replace broken plugs with new ones. Use an engine wiring diagram to check all of the vehicle's wiring; replace damaged or missing wires, and ensure that all are properly connected. If old fuel has been sitting in the ATV's gas tank, it may clog the fuel line or carburetor. Observe whether fuel can travel through the fuel line to the carburetor, and clean or replace a clogged line. Check all connectors and gaskets between the carburetor and fuel line to ensure a tight seal.