Finding and fixing up an old ATV is an exciting journey. I’ve rescued a ton over the years, buying barn finds, fixing and flipping.
An ATV engine that sits for years may have stuck rings or valves. Attempting to start it without first checking engine condition could cause severe damage. Lubing the cylinder and cranking over by hand will minimize risk of damage. Other components that will require attention include:
- Battery and terminals
- Fuel system
- Ignition system
- Oil and filter change
In this post you’ll learn what you should never do to an ATV engine that’s been sitting years. You’ll also learn about the components that will need attention, how to test them and how to fix them. By the end of this post you’ll know exactly what you need to do to get it humming.
Avoid Major Engine Damage
An engine the sits idle, attracts moisture, even on the inside. Moisture given the opportunity turns to corrosion, and that can cause components to stick.
Engine piston rings and valves are components that are susceptible to sticking. Attempting to crank over the engine without following the proper procedure risks breaking the rings and bending valves. Both repairs require lots of dollars and a major strip down.
Juicing her up and trying to start her right away is understandable, your excited to make progress. But when it comes to standing engines, we’ll need to exercise some patience.
The best approach is begin by removing the spark plug and using a suitable funnel 1/2 fill the cylinder with a mix of diesel and paraffin.
Leave the mix sit overnight, it will penetrate and lubricate the cylinder and release the rings if stuck.
The following day, remove the fly wheel plug and using a socket and ratchet turn over the engine gently clockwise by hand. If you feel any resistance, stop turning, remove the valve covers and inspect for sticking valves.
A sticking valve usually needs nothing more than a gentle tap to release.
The battery will be flat and due to sulfation will also be beyond repair, a new battery will be needed. Your battery terminals will also need to be cleaned using grit paper a coating of petroleum Jelly or dielectric grease after installation will prevent corrosion.
When running, the battery charging system will need to be checked, a failed rectifier/regulator is common.
The fuel system will consume the bulk of your attention. It will need a lot of love, unless the bike was stored dry, which isn’t usual. Old gas turns to a gummy sticky deposit and will corrode internal carburettor components.
Most ATV’s will use an mechanical or vacuum slide carburettor. You’ll need to remove the carburettor, and thoroughly clean it in an ultrasonic tank.
While stripped, you’ll need to inspect pilot jet, main jet, needle jet, emulsion tube, float, needle and seat, mix screw. The slide, mechanical or vacuum may need attention too.
Most ATV’s use an acell pump to inject a shot of gas into the carburettor, when the throttle is nailed from idle. The pump diaphragm will need to be replaced and the carburettor leak jet tested.
It’s also very possible, that the carburettor is faulty, old gas can cause a lot of internal damage, sometimes a replacement is a better bet.
Other fuel system components like gas tank need to be cleaned, fuel lines, clamps and vacuum hoses check and replaced if necessary.
Petcock checked, and replaced if it’s a vacuum operated, and fuel filter changed.
A new spark plug, check the cap and plug wire for rodent damage. Ignition systems on barn finds, usually fail after the engine starts and runs a while, so don’t be surprised if you’re diagnosing a no spark at a later time.
A faulty start relay and a faulty solenoid are common. A click noise that resembles a flat battery is the sound of a failed starter solenoid. A failed starter is possible too, but most times it’s just the solenoid.
Oil & Filter
Before you attempt to start the engine, go ahead and drop the oil and filter, the engine will hold a lot of moisture. After the engine’s been running and warm, the oil and filter should be changed again.
The coolant system will need to be flushed, replace the thermostat, rad cap, check hoses – replaced if damaged. Add new coolant and the system will need to be bled, checked for leaks and cooling fan operation checked.
The brake drums or rotors, will likely be corroded and may be seized. Removing, cleaning and replacing pads/shoes should solve that problem.
Brake fluid absorbs moisture and that can cause problems inside a brake system, don’t be surprised if brake calipers are sticking and wheel cylinders leaking.
Brake flexi hoses may also be perished.
Transmission & Axles
Depending on what type transmission you have, you’ll need to change oil and check belts.