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 it by hand will minimize the 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 for 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 that 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. You are excited to make progress. But when it comes to standing engines, we’ll need to exercise some patience.
The best approach is to begin by removing the spark plug and using a suitable funnel fill the cylinder with a mix of diesel and paraffin.
Leave the mix to sit overnight. It will penetrate and lubricate the cylinder and release the rings if stuck. The following day, use the pull starter if fitted or remove the flywheel plug and using a socket and ratchet, attempt to turn over the engine gently by hand. Before actually starting the engine the oil will need to be changed as the lube mix will migrate to the crankcase and contaminate the oil.
If the engine is free to turn over, cranking it a few times will expel the excessive lube mix from the cylinder. Use a shop towel over the plughole to catch the spray.
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. 13 – 14.5 volts indicates all is in order.
A failed stator and rectifier/regulator are common.
See testing stator
The fuel system will consume the bulk of your attention. Carburetor bikes will be a ton more work compared to EFI. Your fuel system will likely 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 carburetor components. Most ATVs will use a mechanical or vacuum slide carburetor.
You’ll need to remove the carburetor and thoroughly clean it in an ultrasonic tank.
While stripped, you’ll need to inspect the pilot jet, main jet, needle jet, emulsion tube, float, needle and seat, mix screw. The slide, mechanical, or vacuum may need attention too. Most ATVs use an acell pump to inject a shot of gas into the carburetor when the throttle is nailed from idle. The pump diaphragm may need to be replaced, and the carburetor leak jet will need to be tested.
It’s also very possible that the carburetor is faulty. Old gas can cause a lot of internal damage. Sometimes a replacement is a better bet.
Other fuel system components like gas tanks need to be cleaned, fuel lines, clamps, and vacuum hoses checked and replaced if necessary.
Petcock checked and replaced if it’s vacuum-operated, and the fuel filter changed.
A new spark plug, check the cap and plug wire for rodent damage. Ignition systems on a barn find 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.
If your bike is water-cooled 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.
Not uncommon for old coolant to turn acidic and damage head gaskets water pumps and frost plugs, you’ll need to pay close attention to the coolant system.
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 are leaking.
Brake flexi hoses may also perish. Replace brake fluid and bleed all calipers.
Transmission & Axles
Depending on what type of transmission you have, you’ll need to change oil and check belts. Front and rear diff oil will need changing before using the bike in anger.
Other Components Which May Need Attention
- Valve lash checked and adjusted
- Oil stem valve seals
- Transmission components
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