ATV Trail Doctor: The ATV Repair Game

ATV Cranks but Won't Start After Sitting

What it does: Cranks strong but never fires. A shot of starter fluid makes it run for a second, then it dies.

Usual cause: Old gas went stale and gummed up the carburetor's tiny pilot jet. Ethanol gas can start going bad in about a month.

Check it yourself: Pull the spark plug right after cranking. If it's bone dry, fuel isn't getting through. Smell the gas. If it smells like varnish, drain it.

Bring it in when: Fresh gas doesn't fix it. The carb needs to come apart and get cleaned. Read how carb cleaning works and what ethanol gas does to small engines.

ATV Clicks but Won't Start

What it does: One click, or rapid clicking. The lights go dim and the engine doesn't turn over.

Usual cause: A weak battery or corroded terminals. ATVs sit a lot, and their small batteries go flat fast without a maintainer.

Check it yourself: A charged 12-volt battery rests around 12.6 volts. If it drops way down (under about 10 volts) while cranking, it's weak. Scrub white or green crust off the terminals and tighten them.

Bring it in when: A new battery goes dead again within a few weeks. That points to the charging system. Here's how to keep a battery alive over winter.

ATV Won't Crank, No Click, but the Lights Work

What it does: Lights are bright. You push start and nothing happens. No click, no crank.

Usual cause: Often the starter relay (also called the starter solenoid), the small part near the battery with two big wire posts.

Check it yourself: Rule out the switches first (see the next problem). Then listen at the relay while someone pushes start. No click with a good battery points at the relay or the circuit that triggers it. Jumping across the relay posts throws sparks, so only do it in neutral and away from fuel.

Bring it in when: You're not sure. We test the circuit before replacing parts, so you don't end up buying a starter you didn't need. ATV repair in Richmond.

ATV Won't Start After Someone Else Rode It

What it does: It ran fine yesterday. Today, nothing happens when you push start.

Usual cause: The red engine stop switch (kill switch) got flipped to OFF. Many quads also won't crank unless they're in neutral or the brake is squeezed.

Check it yourself: Kill switch on RUN, key on, neutral light on, brake squeezed. Then try again. It's free, and it fixes more no-starts than you'd think. More quick checks are in our small engine troubleshooting guide.

ATV Runs Rough, Misses and Pops

What it does: Hard to start, rough idle, and it stumbles and pops when you give it gas.

Usual cause: A fouled spark plug. Riding with the choke on, lots of idling, or running rich coats the plug in carbon.

Check it yourself: Pull the plug and look at it. Light tan or gray is healthy. Wet and black means fouled. White and blistered means it's running lean or hot, and that needs a closer look.

Bring it in when: A new plug fouls again quickly. Something is making it run rich.

ATV Bogs Down and Blows Black Smoke

What it does: Idles fine, but bogs hard and smokes black when you hit the gas.

Usual cause: An air filter packed with mud or dust. The engine gets too much fuel and not enough air.

Check it yourself: Pop the airbox lid and look. Foam filters get washed in filter cleaner, dried, and re-oiled with foam filter oil. Never ride it without a filter. More in ATV maintenance tips for Kentucky riders.

ATV Runs for a While, Then Dies

What it does: Runs great for ten minutes, then sputters and dies. It starts again after it sits for a bit.

Usual cause: A blocked or pinched gas tank vent. Air can't get into the tank, so fuel can't flow out.

Check it yourself: When it dies, loosen the gas cap. If you hear a whoosh and it starts right back up, it's the vent. Look for a kinked vent hose.

Bring it in when: It still dies with the cap loose. An ignition coil that quits when it gets hot can act the same way.

ATV Hard to Start When Hot and Down on Power

What it does: Hard to start (worse when warm), weak and lumpy idle, and it's lost power.

Usual cause: Valves that have tightened up and no longer close all the way, especially the exhaust valve. That leaks compression.

Check it yourself: A compression test will read low. A valve clearance check with feeler gauges tells you whether it's the valves or the rings.

Bring it in when: The clearance is off. It's a precise job. Here's what a valve lash adjustment involves.

ATV Battery Keeps Dying

What it does: You keep putting in new batteries and they keep going dead.

Usual cause: The charging system isn't charging. A burnt stator (the coil under the engine side cover) is a common culprit.

Check it yourself: With the engine revved up, most quads should show roughly 13.5 to 14.5 volts at the battery (check your service manual). If it sits around 12 volts, it isn't charging. A stator AC output test tells a bad stator from a bad regulator.

Bring it in when: The numbers are off. We'll find which part failed before replacing anything. ATV electrical repair.

ATV Overcharging: Bulbs Blowing, Battery Swelling

What it does: Headlight bulbs keep burning out. The battery is swollen or smells like rotten eggs.

Usual cause: A failed voltage regulator/rectifier letting too much voltage through.

Check it yourself: Revved up, voltage well above about 15 volts at the battery means it's overcharging. A swollen battery can leak acid, so wear gloves and eye protection.

Bring it in when: You see it. The regulator needs replacing, and usually the cooked battery too.

ATV Overheating on the Trail

What it does: The temp light comes on after a while on the trail, and coolant spits out of the overflow.

Usual cause: A radiator packed with mud. Kentucky clay dries hard in the fins and blocks the airflow.

Check it yourself: Look through the radiator. Rinse it from the back side at low pressure, because a pressure washer up close folds the fins flat. Check coolant when it's cold, and make sure the fan kicks on.

Bring it in when: The fins are clean, coolant is full, and it still runs hot. That can be the fan, thermostat or water pump. See UTV and side-by-side maintenance for farm work.

Milky Oil After Riding Through a Creek

What it does: It stalled in a creek or deep water. Now the oil looks like a chocolate milkshake.

Usual cause: Water got in through the airbox or vents and mixed with the oil.

Check it yourself: Don't keep cranking it. Pull the plug and crank to push water out of the cylinder. Drain the airbox and dry the filter. Change the oil, run it briefly, and change it again.

Bring it in when: The oil goes milky and it hasn't been in water. That can mean a head gasket or water pump seal.