7 Common Problems with the Yamaha YZ 450F (Explained)

The Yamaha YZ240F is a race-ready motocross bike known for delivering powerful performance, whether racing through the dirt or ripping rugged trails.

That said, even this celebrated racing machine can develop faults, especially considering how hard its owners tend to push it.

This article explores real-life consumer reports to determine the 7 most common problems with the Yamaha YZ450F and offers troubleshooting solutions.

1. Electrical Issues – Pinched Wires

Some Yamaha YZ450F riders report electrical issues resulting in blown fuses. In some cases, fuses blow repeatedly due to pinched wires. Riders report the culprits behind these pinched wires are incorrect wire routing during dealership installation or a misaligned subframe.

“I have a 2020 yz450f. It has 17 hours on it; I bought it used at 13-14. The bike ran flawlessly the two times I took it to the track. The 3rd time I got 3 or 4 minutes in, landed off a jump, the bike coughed, sputtered, and died. I tried to start it for a few minutes, but it would crank, backfire, and not start. After I let it sit for 10 minutes, it would start and idle absolutely perfectly, but as soon as I added any throttle, it would die. I had a friend/diesel mechanic look it over; we found a blown fuse. When replaced, it started to turn over again, but it refused to start. It’s getting spark; all the wiring tested good, it has fuel, the fuel pump is at least kicking on, etc.” vitalmx.com

“Some vital users have posted about an issue with the wire routing for the Wi-Fi controller under the left number plate. If the wiring is on the wrong side of the subframe, it can get pinched by the number plate, and it’s a common installation mistake by dealers.” Vitalmx.com

To fix wiring issues on a Yamaha YZ450F:

• Inspect Wiring:
  • Examine your wiring harnesses, especially around the Wi-Fi controller area.
  • Correct misrouted wires to prevent pinching.
• Check Ignition Components:
  • Verify that the spark plug, ignition coil, and CDI unit are working.
  • Ensure the kill switch and ignition switch function properly.

2. Air Filter Design Clogs Easily

Other YZ450F riders report that the bike’s stock airbox design isn’t ideal for riding in sandy conditions. Fine sand, dust, and dirt particles can clog the air filter rapidly, even if you clean it right before your ride.

“We already ran 25 hours on our yz450f 2018 here and spent more time wrenching than riding. First, the design of the airbox is just a nightmare. In sand condition, you should have a Dyson in the van, remove the cage, and change the filter every 30 minutes. We changed it to the twin air power flow kit, but it’s not better. So we had to change the cylinder and piston after 15 hours.” Vitalmx.com

“I have about 5 hours on mine. I agree with the whole filter thing. I don’t do much riding in sand, but I stay up on my filter after every ride and change it if needed.” Vitalmx.com

To troubleshoot the inconvenient air filter design on your Yamaha YZ450F:

• Inspect your air filter before and after every ride; inspect it during rides when riding in sandy conditions.
• Ensure the airbox cover seals tightly to prevent dust ingress.
• Use a high-quality gasket or sealant if needed.
• Consider upgrading to an aftermarket air filter with improved filtration and airflow.

3. Fuel Pump Issues

Yamaha YZ450F owners report that the fuel pump sometimes runs consistently without rest, draining the bike’s battery. Culprits include faulty wiring, loose connections, or a faulty fuel pump that needs to be replaced.

I have a new 2018 YZ450, which has been running for 2.5 hours. Yesterday, while cleaning the air filter in my shop, I noticed what sounded like the fuel pump engaging every couple of minutes. I disconnected the battery for now…” Thumprtalk.com.

“Mine does it off and on as well. I started it one evening, and then the next morning, I showed up at a race, and the battery was dead (at this point, I had no idea what the pump had been doing). I could jump-start the bike, and after running for 10 minutes or so, it seemed to be ok for the rest of the day.” Thumprtalk.com

“After a couple of weekends of occasional stuttering …my bike would not start. The fuel pump will not energize when kicked. If I hook the fuel pump to a 12v bike battery, the bike starts easily. I replaced the fuel pump and, more importantly, the pressure regulator (which also acts as a check valve) and the smooth condenser. The bike runs perfectly now, with no stuttering. In hindsight, I could have purchased an aftermarket pressure regulator alone, but I put in a new fuel pump kit since it was apart. I got the quantum pump with a lifetime guarantee for $80.” Thumpertalk.com

• Examine the fuel pump wiring for shorts, frayed wires, or corrosion, securing loose connections.
• Inspect the fuel pressure regulator for failure, replacing it as needed.
• Check the battery with a voltmeter, charging or replacing it if necessary.

4. Gearbox Shifting Issues

Some Yamaha YZ450F owners report gearbox noises and shifting issues. Transmission problems can be caused by damaged, worn, or shipped gears, gear misalignment, or worn shifting forks. Faulty gears can rub together, generating metal shavings that can harm other gears.

“It’s been about three months since I bought my new Yamaha YZ450F, and today, it has about 21 hours of use. The other day, climbing a dune, the motorcycle began to make a strange noise only when it ran in the 4th gear (it does not happen in the rest of the gears). Everything indicates that the gear of the 4th gear was broken or that it moved.” Thumpertalk.com

“Started missing third to fourth shifts after I got a new pair of tech 10s last Summer. I figured it was due to the stiffness. The issue got worse, and I saw some metal shavings, so I tore it down and replaced all dog-eared gears and all shift forks (one was cracked) in December. Ran fine for about 15 hours. Maybe a little more. I’m starting to miss shifts again, and there were some metal shavings in the oil today.” Thumpetalk.com

“I have a 2018 YZ450F with less than 25 hours on it, and the third gear is hitting false neutral on heavy load. Other people have said they have experienced the same problem with their 2018 model: a factory defect.” Vitalmx.com

• Have a professional mechanic inspect and diagnose transmission issues before you continue riding.
• Replace any worn gears, shifter fork, etc.
• We suggest taking the bike to an authorized Yamaha mechanic who can report the issues to Yamaha to help track any failure patterns.

5. Air in the Brake Lines

Failing to bleed your brake lines during brake fluid changes can allow air bubbles into the brake system/ That said, some YZ450F riders report that they bleed their brakes and still find air in the system due to worn or faulty master cylinder seals.

“I have a 2007 YZ450, and the rear brake quit working last weekend. The pedal moves full stroke and has no resistance from the master cylinder. If I pump it and try to bleed the brakes, it just dribbles out. I tipped it to the left side and lifted the bike’s rear, but there was still no change. The fluid is full, and I refilled it when trying to bleed the brakes.” Thumpertalk.com

• Re-bleed your YZ’s brake system thoroughly.
• Use a vacuum pump or have a helper pump the brake pedal while bleeding.
• Check the master cylinder piston and seals.
• Replace any damaged components.
• Have a mechanic inspect your internal master cylinder for issues.

6. Timing Chain Issues

Timing chain issues on the Yamaha YZ450F can surface due to a faulty chain tensioner causing slack or overtightening the chain. Another possible culprit is if your YZ’s chain guides are worn, installed incorrectly, or unaligned.

“I have a 2014 YZ450F I bought and used about five years ago; I only do trail riding and dune riding. I am having timing chain issues.  The first time it came loose, I went to start it, and I heard rattling bad, so I shut it off, tore it apart at home, and when I set TDC, the timing was off. I ended up removing the head and inspecting valves for damage, and luckily enough, everything checked out in spec. I installed the head back on, new chain guides, and a chain and tensioner. I Ran the bike for about 18 hours, and it acted up again; I went to start the bike, and it would not crank over; the crank was stuck, so I removed the valve cover to ensure the chain was loose.” Thumpertalk.com

• Ensure your timing chain isn’t worn, damaged, or unaligned.
• Inspect your timing chain tensioner, replacing it if you fail to adjust multiple chains properly.
• Check the timing chain, guides, and sprockets per the suggested intervals in the Yz450F’s owner’s manual.
• Proper timing chain is critical for safe and efficient engine operation—there’s no shame in having a pro diagnose the problem.

7. Clogged Carburetor

Like all other dirt bikes, the Yamaha YZ450F’s carburetor can get clogged occasionally, especially after sitting unused. Carbs get clogged with dirt and debris, obstructing the flow between your jets, air bleeds, and fuel circuits. A faulty accelerator pump can also clog a YZ450’s carburetors.

• Disassemble the carburetor and clean all components.
• Use a welder’s tip cleaner or drill set to remove muck from the carb’s passages.
• Keep the air filter clean to prevent debris from entering the car.
• Don’t allow your YZ450F to sit for long periods without use unless you’ve prepped it with proper winterization.
• Maintain your YZ450 per the service intervals outlined in your owner’s manual.
• Inspect your car after riding hard in wet, muddy, windy, and dusty conditions.

What Are the Pros and Cons of the Yamaha YZ450F?

Pros

• Fast
• Comfortable
• Easy to handle
• Fun to ride
• Celebrated suspension package
• Compact yet powerful 450cc four-stroke racing motor
• Large internal combustion chamber provides increased combustion and raw power
•  Liquid cooling system

Cons

• Electrical Issues – Pinched Wires
• Inconvenient Airbox Design
• Fuel Pump Issues
• Gearbox Shifting Issues
• Air in the Brake Lines
• Timing Chain Failure
• Clogged Carburetor

What Are Some Alternative Models?

What’s the Resale Value of a Yamaha YZ450F?

Sources:

Project YFZ 450 carb and fuel system clean up – YouTube

2022 YAMAHA YZ450F: FULL TEST – Dirt Bike Magazine.

2022 Yamaha YZ250F & YZ450F Review – Cycle News.