1991 Polaris Trail Boss 250 2X4 - The Ultimate Owner'S Survival Guide

There’s a special kind of satisfaction that comes from keeping a classic machine alive and kicking. If you own a 1991 Polaris Trail Boss 250 2×4, you know exactly what we’re talking about. You’ve got a piece of ATV history that’s simple, rugged, and an absolute blast on the trails.

But let’s be honest, a machine of this vintage comes with its own set of quirks and challenges. You’ve probably spent some time scratching your head over a weird noise or a stubborn starting issue.

Here at FatBoysOffroad, we promise this is the only 1991 polaris trail boss 250 2×4 guide you’ll ever need. We’re going to break down everything from pre-ride checks and routine maintenance to diagnosing those common problems that can ruin a weekend. Get ready to turn that wrench with confidence and keep your Trail Boss ripping for years to come.

Why the 1991 Polaris Trail Boss 250 2×4 is Still a Trail Legend

Before we dive into the nuts and bolts, let’s appreciate what makes this machine so special. In an era of complex, computer-controlled ATVs, the old Trail Boss stands out for its beautiful simplicity.

The air-cooled, 244cc two-stroke engine is a masterpiece of straightforward engineering. There are no radiators to flush, no complicated valve trains to adjust, and no fuel injection systems to diagnose. It’s an engine you can understand just by looking at it.

Key Benefits of Owning a Classic Trail Boss

The benefits of a 1991 polaris trail boss 250 2×4 go far beyond nostalgia. For the DIY mechanic and trail rider, this ATV offers some serious advantages:

Easy to Work On: With basic hand tools like a socket set, screwdrivers, and pliers, you can perform nearly all the essential maintenance yourself. Parts are generally accessible and easy to understand.
Durable Design: These ATVs were built tough. The steel frame and simple suspension can handle a surprising amount of abuse on the trail.
Lightweight and Nimble: As a 2×4 model, it’s lighter than its 4×4 counterparts, making it feel quick and responsive on tight, twisty trails. It’s a fantastic machine for learning fundamental riding skills.
Affordable Fun: Both the initial purchase price and the cost of ownership are significantly lower than modern ATVs, making it an accessible entry point into the off-road world.

Your Essential 1991 Polaris Trail Boss 250 2×4 Pre-Ride Checklist

The single best way to prevent problems on the trail is to catch them in the garage. A thorough 5-minute pre-ride inspection is one of the most important 1991 polaris trail boss 250 2×4 best practices you can adopt. Make this a habit every single time you ride.

We call it the T-CLOCS method, a term common with motorcyclists that works perfectly here:

T – Tires & Wheels: Check tire pressure (usually 3-5 PSI, check your tire sidewall). Look for cracks, punctures, or damage. Grab each wheel and check for wobbly bearings.
C – Controls & Cables: Squeeze the brake levers. Do they feel firm, not spongy? Test the throttle—it should snap back cleanly when you release it. Check that the cables aren’t frayed or kinked.
L – Lights & Electrics: Test the headlight (high and low beam) and the taillight. Make sure the kill switch works properly.
O – Oil & Fluids: This is a two-stroke, so your primary concern is the two-stroke injection oil tank. Make sure it’s full. Use a quality two-stroke injector oil. Also, check the transmission/gear case oil level via the dipstick or sight glass.
C – Chain & Chassis: Inspect the drive chain. It should have about 1/2 to 3/4 inch of slack. Look for tight spots or rust. Lube it if it looks dry. Glance over the frame for any cracks, especially around welds.
S – Stands & Suspension: Check that nothing is loose in your suspension components. Push down on the front and rear of the ATV to make sure the shocks rebound smoothly.

Common Problems with the 1991 Polaris Trail Boss 250 2×4 (And How to Fix Them)

Even with great care, you’ll eventually run into issues. Here are the most common problems with a 1991 polaris trail boss 250 2×4 and a clear path to troubleshooting them.

Problem 1: It Won’t Start or is Hard to Start

This is the most frequent complaint. The solution almost always comes down to three things: fuel, spark, and air.

Check for Spark: Get a spark plug socket and remove the spark plug. Keep it connected to the plug wire, touch the threaded part to the engine block, and pull the starter. You should see a strong, blue spark. No spark? The issue could be the plug, plug wire, coil, or CDI box. A new NGK B8ES plug is always the cheapest place to start.
Check for Fuel: Is the petcock (fuel valve) on? Is there fresh gas in the tank? Old gas is a common culprit. If it’s been sitting, drain the tank and the carburetor bowl and start with fresh fuel mixed with a little Sea Foam.
Check the Carburetor: The pilot jet in the Mikuni carburetor is notoriously tiny and clogs easily. If the ATV has been sitting, you will almost certainly need to remove the carb, disassemble it, and clean the jets with carb cleaner and compressed air. This is the most likely cause of a no-start issue.

Problem 2: The Engine Bogs Down or Has No Power

If the engine starts but sputters or bogs when you give it throttle, you’re likely dealing with a fuel or air delivery problem.

Dirty Air Filter: A clogged air filter will choke the engine. Pull it out and clean it with filter cleaner or wash it in warm, soapy water. Let it dry completely and re-oil it with proper foam filter oil.
Clogged Main Jet: Similar to the pilot jet, the main jet in the carb can get gummed up, starving the engine of fuel at higher RPMs. A thorough carb cleaning is the fix.
Exhaust Obstruction: The spark arrestor screen in the muffler can get clogged with carbon. Remove it (usually a single screw) and clean it with a wire brush until you can see through it clearly.

Problem 3: The Chain Keeps Falling Off

A loose or misaligned chain is not only annoying but also dangerous. This is a common wear-and-tear issue.

To fix this, locate the two large bolts on either side of the rear axle carrier. Loosen them slightly. You’ll see an adjustment mechanism (often an eccentric carrier you can turn with a large wrench or spanner tool). Rotate the carrier to tighten the chain until you have about 1/2 to 3/4 inch of slack in the middle. Make sure the axle is straight, then retighten the carrier bolts to spec. If the sprockets look like sharp, pointed shark teeth, they are worn out and must be replaced along with the chain as a set.

A Practical Maintenance Schedule: The Ultimate Care Guide

This is the core of our 1991 polaris trail boss 250 2×4 care guide. Following this schedule will dramatically increase the life and reliability of your machine.

After Every Ride

Wash the ATV to remove mud and dirt.
Clean and lube the drive chain.
Check tire pressure.

Every 10-15 Hours of Riding

Clean and re-oil the air filter.
Check and top off the two-stroke injector oil.
Inspect and adjust chain tension.
Check all nuts and bolts for tightness, especially on wheels and suspension.

Every 50 Hours or Annually

Change the transmission/gearbox oil. Polaris AGL is recommended, but check your manual.
Replace the spark plug.
Inspect brake pads for wear.
Grease all zerk fittings on the suspension and steering components.

Sustainable & Eco-Friendly Riding: Best Practices for Your Classic ATV

Part of being a responsible rider is protecting the trails we love. Embracing a sustainable 1991 polaris trail boss 250 2×4 mindset is easier than you think.

When performing maintenance, always have a plan for used fluids. Never dump oil or coolant on the ground. Store it in a sealed container and take it to your local auto parts store or recycling center. Many places will take it for free.

Consider using biodegradable chain lube and cleaners. These products are designed to break down naturally, reducing their impact on the environment. An eco-friendly 1991 polaris trail boss 250 2×4 is one that’s well-maintained to prevent leaks and runs efficiently to minimize emissions. The most important practice? Always stay on designated trails to prevent erosion and protect wildlife habitats.

Frequently Asked Questions About the 1991 Polaris Trail Boss 250 2×4

What kind of oil should I use in my 1991 Trail Boss 250?

For the engine, you need a high-quality 2-stroke injector oil designed for air-cooled engines. For the transmission, Polaris AGL Synthetic Gearcase Lube is the factory recommendation, but a comparable 75W-90 gear oil can often be used. Always check your service manual to be certain.

What is the correct spark plug for a 1991 Trail Boss 250?

The standard and most reliable spark plug is the NGK B8ES. It’s a good idea to always keep a spare one in your toolkit.

How do I mix gas for my Trail Boss if the oil injector fails?

If you suspect the oil injection system isn’t working, you MUST pre-mix your fuel to avoid seizing the engine. Disconnect the oil line and cap the intake port. A safe pre-mix ratio is 40:1, which is 3.2 ounces of 2-stroke oil per 1 gallon of gasoline.

Where can I find parts for such an old ATV?

You’d be surprised! Many parts are still available through online retailers like Rocky Mountain ATV/MC, Dennis Kirk, and even Amazon or eBay. Focus on finding OEM part numbers and then searching for those numbers.

Keeping a classic like the 1991 Polaris Trail Boss 250 2×4 on the trail is a rewarding journey. It teaches you the fundamentals of mechanics and connects you to a simpler era of off-roading. By following these tips, performing regular maintenance, and not being afraid to get your hands dirty, you’ll ensure your vintage machine provides endless fun for years to come.

Now, grab your tools, get out in the garage, and get that Trail Boss ready for its next adventure. Happy trails!

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Thomas Corle

Founder & Automobile expert at FatBoysOffroad

Automobile expert and off-road enthusiast, sharing in-depth knowledge of vehicles, gear, and adventures. Helping readers make smart decisions and enjoy the thrill of off-roading safely and confidently.