The Yamaha Big Bear 350, a workhorse of the ATV world, has earned a reputation for reliability and ruggedness. But even the toughest machines can face challenges. If you're a proud owner of a Big Bear 350, or considering becoming one, it’s crucial to be aware of some common issues that might arise. Understanding these potential problems can help you keep your ATV running smoothly for years to come.

This article is designed to be your comprehensive guide to navigating the potential pitfalls of owning a Big Bear 350. We'll explore the common problems, offer practical solutions, and equip you with the knowledge to keep your Bear in top condition. Let's dive in!

Uh Oh, My Big Bear Won't Start! What Could It Be?

A non-starting ATV is arguably the most frustrating issue. Thankfully, the Big Bear 350's starting problems often stem from a few easily diagnosable areas.

  • Battery Blues: This is the most common culprit. A weak or dead battery simply won't provide enough juice to crank the engine.

    • Solution: Check the battery terminals for corrosion and clean them thoroughly. Ensure the battery is fully charged. If the battery is old (3+ years), consider replacing it. A load test can help determine if the battery is truly failing.

  • Spark Plug Problems: A fouled or damaged spark plug can prevent the engine from firing.

    • Solution: Remove the spark plug and inspect it. Look for signs of excessive carbon buildup, oil fouling, or damage to the electrode. Clean or replace the plug as needed. Ensure the spark plug gap is set to the manufacturer's specification.

  • Fuel Delivery Issues: The Big Bear 350 relies on a carburetor to deliver fuel to the engine. Problems here can lead to starting difficulties.

    • Solution:
      • Check the Fuel Tank: Make sure there's fuel in the tank! Sounds obvious, but it happens.
      • Fuel Line Obstructions: Inspect the fuel lines for kinks, cracks, or blockages. Replace any damaged lines.
      • Carburetor Cleaning: A dirty carburetor is a frequent offender. Over time, varnish and debris can clog the jets and passages, preventing proper fuel flow. Cleaning the carburetor involves disassembling it, soaking the parts in carburetor cleaner, and reassembling it carefully. This might be a job for a professional if you're not comfortable with small engine mechanics.

  • Ignition System Woes: While less common, problems with the ignition system can also prevent starting.

    • Solution:
      • Check the Ignition Coil: Use a multimeter to test the ignition coil's resistance. If it's outside the specified range, the coil may be faulty.
      • Inspect the Wiring: Look for damaged or corroded wiring in the ignition system. Repair or replace any faulty wiring.

My Big Bear is Running Rough! Time to Investigate

A rough-running engine can indicate several underlying issues. Identifying the symptoms can help narrow down the cause.

  • Carburetor Troubles (Again!): A dirty or improperly adjusted carburetor is often the cause of rough running.

    • Solution: Consider a thorough carburetor cleaning and adjustment. Pay close attention to the idle mixture screw, which controls the air-fuel mixture at idle. Adjusting this screw can often smooth out a rough idle.

  • Vacuum Leaks: Vacuum leaks can disrupt the air-fuel mixture, leading to rough running and poor performance.

    • Solution: Inspect all vacuum lines for cracks or disconnections. Pay particular attention to the intake manifold gasket and carburetor boot. Use a spray bottle with soapy water to check for leaks. Spray around potential leak areas while the engine is running. If you see bubbles forming, you've found a leak.

  • Valve Problems: Worn or improperly adjusted valves can cause rough running and loss of power.

    • Solution: Check the valve clearances according to the manufacturer's specifications. Adjust the valves as needed. This requires specialized tools and knowledge, so it might be best left to a qualified mechanic.

  • Air Filter Issues: A dirty or clogged air filter can restrict airflow to the engine, leading to rough running and reduced power.

    • Solution: Clean or replace the air filter regularly. The frequency of cleaning depends on the riding conditions. Dusty or muddy conditions require more frequent cleaning.

Big Bear Brakes: Squealing, Grinding, and Just Plain Bad!

The braking system is crucial for safety, so addressing brake problems promptly is essential.

  • Worn Brake Pads: This is the most common brake problem. As brake pads wear down, they lose their ability to effectively grip the rotor.

    • Solution: Inspect the brake pads regularly. Replace them when they reach the wear limit. Ensure you use high-quality replacement pads.

  • Contaminated Brake Pads: Oil, grease, or other contaminants on the brake pads can reduce their effectiveness and cause squealing.

    • Solution: Clean the brake pads with brake cleaner. If the contamination is severe, you may need to replace the pads. Also, inspect the brake system for leaks that could be causing the contamination.

  • Sticking Calipers: A sticking caliper can cause the brakes to drag, leading to overheating and premature wear.

    • Solution: Clean and lubricate the caliper slides. If the caliper is severely corroded, you may need to rebuild or replace it.

  • Air in the Brake Lines: Air in the brake lines can make the brakes feel spongy and less effective.

    • Solution: Bleed the brake lines to remove any air. This requires a brake bleeder tool and some mechanical knowledge.

Transmission Troubles: Shifting Problems and More

The Big Bear 350's transmission is generally reliable, but problems can occur.

  • Difficult Shifting: Difficulty shifting gears can be caused by several factors.

    • Solution:
      • Check the Shift Linkage: Inspect the shift linkage for wear or damage. Lubricate the linkage to ensure smooth operation.
      • Adjust the Clutch Cable: An improperly adjusted clutch cable can make shifting difficult. Adjust the cable according to the manufacturer's specifications.
      • Check the Transmission Oil: Low or contaminated transmission oil can cause shifting problems. Change the transmission oil according to the recommended service interval.

  • Slipping Clutch: A slipping clutch can cause a loss of power, especially when climbing hills or accelerating.

    • Solution:
      • Adjust the Clutch Cable: Make sure the clutch cable has the correct amount of free play.
      • Replace the Clutch Plates: If the clutch plates are worn, they will need to be replaced. This requires disassembling the clutch assembly.

Electrical Gremlins: Lights, Starting, and More!

Electrical problems can be frustrating to diagnose, but a systematic approach can help.

  • Blown Fuses: Blown fuses are often a sign of a short circuit.

    • Solution: Replace the blown fuse with a fuse of the same amperage. If the fuse blows again immediately, there is likely a short circuit in the wiring.

  • Faulty Wiring: Damaged or corroded wiring can cause a variety of electrical problems.

    • Solution: Inspect the wiring harness for damage. Repair or replace any damaged wiring. Use dielectric grease on electrical connections to prevent corrosion.

  • Lighting Issues: Problems with the headlights or taillights can be caused by blown bulbs, faulty wiring, or a bad switch.

    • Solution: Check the bulbs first. If the bulbs are good, check the wiring and the switch. Use a multimeter to test the voltage at the light socket.

My Big Bear is Overheating! What's Going On?

Overheating can cause serious engine damage, so it's crucial to address it promptly.

  • Low Coolant Level: Low coolant level is the most common cause of overheating.

    • Solution: Check the coolant level in the radiator and the overflow tank. Add coolant as needed. Use the correct type of coolant recommended by the manufacturer.

  • Radiator Problems: A clogged or damaged radiator can restrict coolant flow and cause overheating.

    • Solution: Clean the radiator fins to remove any dirt or debris. Inspect the radiator for leaks. If the radiator is severely damaged, it may need to be replaced.

  • Faulty Thermostat: A faulty thermostat can prevent the engine from cooling properly.

    • Solution: Test the thermostat to see if it opens and closes properly. Replace the thermostat if it is faulty.

  • Water Pump Issues: A failing water pump can reduce coolant flow and cause overheating.

    • Solution: Inspect the water pump for leaks or damage. Replace the water pump if it is faulty.

Frequently Asked Questions

  • Why does my Big Bear 350 backfire?
    Backfiring can be caused by a lean fuel mixture, exhaust leaks, or ignition timing problems. Start by checking the carburetor and exhaust system for leaks.

  • How often should I change the oil in my Big Bear 350?
    Change the oil every 100 hours of riding or at least once a year, whichever comes first. More frequent changes are recommended for heavy use or dusty conditions.

  • What type of oil should I use in my Big Bear 350?
    Use a high-quality 10W-40 motorcycle oil that meets the JASO MA specification. This ensures proper lubrication for the engine and clutch.

  • How do I adjust the carburetor on my Big Bear 350?
    The carburetor adjustment procedure varies slightly depending on the model year. Consult the service manual for the correct procedure. Generally, you'll adjust the idle speed and the idle mixture screw.

  • Where can I find a service manual for my Big Bear 350?
    Service manuals can be purchased online from various retailers or directly from Yamaha. They are invaluable for performing repairs and maintenance.

Keeping Your Big Bear Roaring

Owning a Yamaha Big Bear 350 can be a rewarding experience, especially when you're prepared to tackle common maintenance and repair tasks. By understanding the potential problems and following the solutions outlined in this guide, you can keep your Big Bear running strong for years to come. Remember, regular maintenance and prompt attention to issues are key to maximizing the lifespan and performance of your ATV.