5 Most Common Problems With Yamaha YZ 250F (Explained)

The Yamaha YZ 250F is a five-valve off-road motocross bike with a four-stroke engine.

It features a slimmed-down frame including a narrow fuel tank and is specifically designed for shredding the track and dust-ruffling the trail.

The reliable carburated classic was updated with a fuel-injected engine back in 2014, making it even more powerful and efficient.

But no motocross dirtbike is perfect; what are the common problems with a Yamaha YZ 250F?

Scroll down to find out!

1. Yamaha YZ 250F Won’t Start

One of the chief complaints among YZ 250F owners is that the dirtbike has trouble starting, particularly after it’s been sitting for a while. This is due to the gas having a shorter-than-average shelf life due to the bike’s plastic gas tank.

Let’s take a look at a real-life example from a YZ 250F-owner testimonial:

“[My Yz 250F] the bike won’t kick start. I tried for at least 45 minutes just kicking it over, and nothing really happened. So I decided to push it up the road and try and bump-start it, and it started! But I quickly realized something was wrong, and it died almost immediately after. I later discovered this is because the clutch won’t engage. I can try and push the bike, but the back wheel won’t turn when it’s in gear, even with the clutch pulled in. The bike is a 2009 and has about 160 hours on it since I’ve got it. I change the oil every 8 hours and clean the filter every 5-10 hours, depending on how dusty it is. I’ve never rebuilt it, and I’ve never adjusted the valves, although it always starts 1st kick cold or hot….”

Four-stroke fuel only lasts about 20 days when stored in a plastic fuel tank. If the fuel expires and begins to decompose, it can clog the accelerator pump circuit, causing the YZ 250F to have problems starting.

The expired fuel does more than throw a wrench in the ignition sequence; it can also burn out your spark plugs altogether, which will cause starting problems even after you’ve changed out the fuel.

As the rider mentioned in the quote above, the resulting combination of problems can also include a stuck clutch.

• The good news is that getting the bike to start is as simple as draining the fuel out, inspecting your spark plugs, and replacing them as needed.
• The clutch should take care of itself once the bike fires up, though we suggest trying your best to roll it into neutral before you start it. 
• If you ran expired fuel through a pre-2014 year model, you’d want to rebuild your carburetor as well, as decomposing fuel can clog other carburetor components.

If it’s not the gone-off gas, the most common reason a YZ 250F won’t start is due to a flat battery.

2. Yamaha YZ 250F Shock Linkage Siezed

I’ve heard multiple YZ 250F owners describe a similar common problem; their shock linkage gets stuck.

While more than a few of these claims were said to have occurred in cold weather, it’s possible that once your linkage jams up, they stay seized in warm weather too.

The source of your YZ 250F’s seized or jammed shock linkage is likely the bolts and bushings in the shock. Inspecting, cleaning, and properly greasing these are part of routine maintenance. Failure to do so results in jammed linkage.

• If you can remove the bolts and bushings, clean them and check their cognition.
• If they’re not stripped or damaged, lube them up with the proper grease and reassemble them.
• If you replace the bolts, bushings, or both, be sure to lubricate the new components before installing them.

3. Yamaha YZ 250F Leaking Valves

The YZ 250F’s power-and-performance-packed engine utilizes a system of valves, the number of which varies between five and four, depending on the year model.

All YZ 250F models will require a routine valve inspection per the intervals outlined in the owner’s manual. Failing to do so can result in leaking engine valves, which can put more than a damper on your weekend motocross plans.

A valve leak is significantly less obvious to detect than you might think, or as this real-life owner puts it:

“Pulled head, took out the valves, and all the seats and faces were fine. No pits, no erosion, no black lines. Now I’m baffled. Haven’t pulled the cylinder off yet, but the cylinder itself is clean and looks perfect. Maybe 2500 miles and not even a ridge.

The bottom of the cylinder and valves and the top of the piston are clean, just solvent required to clean, probably because the jetting came together. Most of last year, the bike was too rich. There was a LOT of carbon on the exhaust valve stems below the guides and a very hard thick ring of crud just inside the faces.”

The valves on the pre-2008 year models were known to stretch and bend at high revs, causing valve leaks and resulting in a loss of engine compression.

If this sounds familiar, you’re not alone. While valve leaks are more common on the older iterations motocross model, they’re equally hard to detect on all YZ 250F models.

Like the Yahm owner quoted above, you might clean all that carbon off and reinstall everything looking spic and span, only to find that you still have no valve compression!

The owner’s manual suggests pouring solvent through to check for leaks, but the solvent suggested doesn’t always show the leak.

This is often the source of confusion for frustrated YZ 250F owners, but there are ways of detecting the valve leaks.

• The solvent is sometimes too thick to pour through the leaking valve, which may only be marginally off.
• Using contact cleaner is still safe, and its thinner viscosity allows it to pour through even subtle valve leaks, highlighting the opening that’s causing your bike’s compression loss.

4. Yamaha YZ 250F Engine Stalls and Locks Up

While this wasn’t a particularly widespread issue, it caused enough of a buzz in the online community to warrant coverage.

Not to mention, the YZ 250F is sought after in the used motocross market – this section is important information for any window shoppers to keep in mind.

In 2014, multiple occurrences of engine stalls, lock-ups, and rod failures resulted in Yamaha recalling many of the 2015 year models manufactured between May 2014 and November 2014.

An engine lock-up on a motocross bike is as serious as it sounds and can cause a collision that results in injuries, some of which could be serious or even fatal.

The models affected were reported to be blue and white or red and white.

Yamaha contacted any owners of suspect 2015 year model YZ 250Fs and encouraged them not to ride their bikes until scheduling an appointment with their local Yamaha dealership and allowing the technicians to inspect the engine for safety.

Dealerships were instructed to inspect and repair any engine issues without charge to the customer.

However, the notice gave no information regarding the cause of the engine failure, leaving some owners in anxious speculation about whether the technicians knew what to look for.

I’ve heard rod failure mentioned as the leading cause but was unable to confirm this with literature from Yamaha themselves.

• We encourage both owners and window-shoppers of the 2015 year model YZ 250Fs to check their VIN numbers and cross-reference them with the recall notice.
• The dealership would be able to tell you if the bike had been inspected for approval or repair during the time of the recall. If it hasn’t been, hold them to that free inspection before you ride.

Unfortunately, this wasn’t the first YZ 250F recall to unfold in 2014; the next section explains more.

5. Yamaha YZ 250F Drive Train Can Detach

In February 2014, Yamaha recalled about 1,300 of their off-road motocross competition models, including the YZ 250F, due to multiple occurrences of drive chains detaching while riding.

In fact, this issue affected all two-wheel off-roaders with model numbers YZ250FEL, YZ250FEW, YZ450FEL, and the YZ450FEW.

If your YZ 250F was manufactured or sold between December 2013 and January 2014, it should have been part of this recall and taken in for drive train inspection, approval, and, if applicable, repair, upgrade, and replacement.

If you’re experiencing drive train issues on a 2013-2014 YZ 250F, we suggest you refrain from riding until you’ve had your drive train inspected by a Yamaha technician.

Even if you’ve yet to experience symptoms, if you missed the recall back in 2014 or bought your bike used after it all went down, having your drive train inspected by a pro might spare you time, money, and injury down the road.

Related: 6 Most Common Kawasaki KX 250 Problems (Explained)

Pros and Cons

Pros

• A true motocross competition bike with lightweight handling and raw, accessible engine power.
• Fun to ride.
• Reliable.
• Long-lasting.
• Newer models interface with an engine tuning app on riders’ phones that allows for endless engine tuning options without the need for aftermarket upgrade installations and without risking engine damage or warranty voiding. 

Cons

• Plastic fuel tank causes gas to expire early and start problems.
• Shock linkage jams in cold weather.
• Valves Need Frequent Inspection and Might Leak, especially pre-2008 models.
• Engine Locks Up and Stalls on the 2015 year models.
•  Drive Train Might Detach on the 2014 year models.

What Do the Reviews Say?

“On to the suspension. The blue bikes have set the standard for suspension in recent years, and, once again, the YZ’s KYB components worked as well as we could have hoped for right out of the box. We set the sag at 104mm and felt confident enough to click off laps after just a few corners. The Speed Sensitive System (SSS) forks offered that sought-after cloud-like feel while absorbing chatter bumps with a progressive dampening as the bike dove deeper into the stroke.”

“I did struggle a bit with the front end through some of the faster-banked corners. The forks seemed to sit high in the stroke for the majority of the turn. This gave the front end a vague, chopper-ish feeling that would bite when the bars were turned and the front wheel was on the edge of knifing. The Yami boys took to the clickers, taking two out on compression and one out on rebound. These adjustments allowed the fork to settle into the corner better and gave me much more confidence in turning with the front end. The overall chassis balance and clicker changes made holding the faster outsides or slicing through tight 180s nearly effortless.”

“The rest of the bike could be described in one word: smooth. Clutch pull—smooth. Transmission—smooth. Braking—smooth. It’s been a year since I rode a Yamaha YZ250F, and I was once again impressed with the machine’s overall user-friendliness. Shifting the bike requires minimal effort, the same with using the clutch. Grab another gear or slip the clutch without fear of arm pump or exhaustion.”

“I always try to test bikes from a consumer point of view. I want to see which bike is the easiest to go the fastest on. In my mind, the bike that I can turn the fastest laps on with the least amount of effort would be the best bike for me. Obviously, this might be different for each rider, but some characteristics (suspension, cockpit, etc.) can be well-liked across the industry. The Yamaha hit all my marks in this category as I smoothly burned through a 20-minute moto. Riding this bike is fun and easy, something dirt bikes should be!”

Source: https://www.cyclenews.com/2020/11/article/2021-yamaha-yz250f-review/

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Sources:

• https://ultimatemotorcycling.com/2014/12/23/2015-yamaha-yz250f-recall-due-engine-lock/
• https://www.cpsc.gov/Recalls/2014/Yamaha-Recalls-Off-Road-Motorcycles#:~:text=Recall%20Details&text=This%20recall%20involves%20two%2Dwheeled,white%2C%20or%20red%20and%20white.
• https://www.cyclenews.com/2020/11/article/2021-yamaha-yz250f-review/