8 Common Honda CRF125F Problems (Explained)

The Honda CRF125F is a popular dirt bike. Its motor is small yet powerful enough to be ideal for beginners still learning the subtle nuances of trail riding.

But like all dirt bikes, the Honda CRF125F is prone to a few problems.

This article outlines the top 8 rider issues, their symptoms, and troubleshooting tips.

1. Poor Engine Idle

Some Honda CRF125R owners complain about poor idling. Idle issues on a CRF125F could mean a clogged pilot jet, wrong fuel screw, or dirty air filter.

“My friend’s bike is a 2017 CRF 125 Fb. The bike has a tough time idling, even when warm. I have no idea what could be wrong. Also, when dumping the throttle, the engine starts to choke and splutter and, if kept up, will die.” reddit.com

To fix poor engine idling on a Honda CRF125R:

• Inspect the pilot jet—clean and rebuild as needed.
• Inspect the fuel screw and adjust or replace if necessary.
• Inspect the air filter and unclog or replace it if dirt prevents airflow.

2. Faulty Engine Timing

Other Honda CRF125F riders report faulty engine timing. Possible causes of timing issues on a Honda CRF125F include faulty timing chains, chain tensioners, or sheered flywheels.

“I was told my CRF had a top and bottom end rebuild; the whole thing needed to be redone. The bike had a new Wiseco crank, a cylinder that works 13.5:1 compression piston, a brand new std size jug, a new timing chain, and a used tensioner that’s in good working shape. I’ve had the cylinder head done by Ken (new seats with kW intake and exhausts). My problem is this:

When setting my timing, I can get the cam to sit level with the head and the punch mark on the crank to line up with the Arrow, BUT the two marks on the flywheel are off by about 1/2 inch.” – crfsonly.com

To fix faulty engine timing on a Honda CRF125R:

• Check the balancer shaft gears’ condition and alignment.
• Inspect the timing chain and its tensioner for damage, crud, and wear and tear.
• Check the flywheel and flywheel critical condition.
• Replace worn parts as needed.

3. Won’t Shift Into Gear

Other Honda CRF125F riders report their dirt bikes won’t shift into gear. Shifting issues are often caused by a faulty clutch lever, a poorly adjusted clutch cable, or a bent shift shaft interfering with the bike’s gear selector.

“2020 crf125f – won’t shift into gear: My son was riding his bike today and went to take off, and it will not shift into gear now. I was able to get it into first, but it grinds, and then I noticed he had been riding it with one of the wires unhooked on the clutch lever, so I’m not sure if that caused an issue…” – crfsonly.com

To troubleshoot a Honda CRF125R that won’t shift into gear:

• Inspect the clutch lever and its safety switch—adjust and replace as needed.
• Examine the clutch cable—adjust it to 1/8-1/4 inch of cable free play at the lever.
• Inspect the shift shaft for any damage or misalignment—repair and replace if necessary.

4. Hard to Start

Owners claim their Honda CRF125Rs can be hard to start due to faulty ignition switch, fuel pump or fuel pump relay failure, or corroded wiring in the starting system.

“Having some trouble and needing some help.  I have a 2021 CRF 125F BW that no longer starts.  The problems started when it would periodically fail to run the fuel pump or turn the fuel light on when I turned the key.  I would repeatedly turn the key, and it would eventually work. The engine cut out the last time I rode it, and it wouldn’t start after that.  I’ve checked all electrical connections, swapped both fuses, and replaced the battery. When I turn the key, the green light under the kill switch lights up, but that is it…” -thumpertalk.com/

To troubleshoot a CRF125F that’s hard to start:

• Test the ignition switch with a multimeter—compare the readings with the wiring diagram listed in the service manual for your particular year model CRF125F.
• Inspect and clean the wiring for corrosion, replacing damaged and burnt wires as needed.
• Check your fuel pump and pump relay with a multimeter, replacing them if they lack voltage or electrical continuity.

5. Suspension Too Soft

Riders sometimes complain that their Honda CRF125F’s suspension is too soft for large or aggressive riders, bumpy roads, and jumps. Since the bike is designed and tuned for entry-level dirt bike riding, riding hard and aggressive trails can cause bottoming out and poor handling.

To troubleshoot a Honda CRF125F with suspension that feels too soft:

• Replace the stock suspension springs with a stiffer aftermarket setup.
• Use fork oil with a thicker viscosity.
• Adjust the preload in the rear shock to compensate for the soft front.
• Upgrade from entry-level to a dirt bike designed for more aggressive trail riding.

6. Clutch Slips Too Easily

Riders report their clutch slips frequently on their Honda CRF125F. Causes of a slipping clutch include worn friction disks, weak clutch springs, contaminated or leaking transmission oil, or damaged clutch plates.

“After calling four shops, I got the specs for the CRF125F clutch hub nut (55 lbs.). None of the shops could find the specs for the “oil filter rotor nut” on Honda’s website, and none have the paper manual. All these shops I called suggested a different torque value (a guess) to use. I ended up using the spec for the clutch hub on the oil filter rotor, as the nuts are pretty much the same.  After getting it back together, the clutch lever pull is very light, but it seems to operate normally. I wish I would’ve replaced or upgraded the springs, but typically, when I do a clutch, the springs are fine, so I didn’t anticipate their need. So I rode it again, and the clutch slipped too easily; I thought the springs got too hot and weren’t grabbing hard enough anymore. Wheelies are impossible; clutch just slips if I try, and the cable is adjusted properly.” – ThumperTalk.com

To troubleshoot a slipping clutch on a Honda CRF125F:

• Check the clutch components, such as the friction disc, pressure plate, and springs, for wear or damage.
• Ensure the clutch cable is adjusted correctly, providing enough tension to engage the clutch.
• Consider upgrading the clutch springs if they’re not rigged enough for your riding style.
• Verify that there’s no oil contamination on the clutch components.

7. Carburetor Problems

One of the most common issues on the Honda CRF150F, and on most dirtbikes, is blocked or poorly adjusted carburetors. Dirt and grime buildup clogs the carb’s fuel pathways, and improperly adjusted air/fuel screws can affect idling and engine performance.

Furthermore, some riders replace their jets with incorrect sizes for the riding conditions, including climate, altitude, and air pressure. Incorrect jet sizes affect the air-fuel ratio of their CRF125F.

“I purchased a new 2016 CRF150F for my son. He got one ride out of it bone stock. I then went thru the power-up process: removed the airbox snorkel, removed the exhaust baffle, purchased from CRFs Only the needle, installed it on the 4th notch, new fuel screw, new pilot, and main jet. No matter what position I set, the fuel screw in the bike bogs badly past 1/4 throttle. It starts and idles like a dream, and I can ride in 1st gear into higher RPM. I can’t crack the throttle past 1/4 without it cutting out and wanting to die… I confirmed everything is nice and clean inside the car; I can see the light through the jets, which are brand new.” – crfsonly.com

To troubleshoot carburetor problems on a Honda CRF125F:

• Remove and clean the carburetor thoroughly, paying attention to jets and passages.
• Check that your CRF has the correct jet sizes (main and pilot) installed for the environment you’re riding trails in.
• Fine-tune the air/fuel mixture by adjusting the screw slightly until you achieve the desired engine performance.
• Inspect the area around the carburetor joints or intake manifold for vacuum leaks–even a tiny leak can impact performance.
• There’s no shame in taking your bike to a Honda-literate mechanic in your area who knows the ideal carb settings for your CRF125F.

8. Leaking Fork Seals        

CRF125F owners report leaking fork seals, whether from sharp rocks puncturing seals or nicking the fork tube or from trapped dirt lodged in the fork breaking the seal, leading to oil leakage. Fork seals wear out over time on all bikes, typically lasting between 20 and 80 hours, depending on the terrain.

“I finished a race last weekend and rolled my son’s CRF into the trailer… The fork legs were dripping with oil. This is the third set of fork seals in less than a year. I wonder if that inner chamber leaks oil and moves into the outer chamber. Would it be possible that the seals are leaking because too much oil accumulates in the outer chamber, and when the pressure builds, it passes oil through the seals? The damper O-rings were leaking pretty badly….. The left one was half full(not half empty) upon disassembly. When I compressed the rod, oil would ooze out of the rod. So all that oil was emptying itself into the outer chamber.” – crfsonly.com

• Remove dirt and debris from the seal using a unique tool or a business card.
• Ensure the fork tubes have the correct oil level and that the oil isn’t contaminated or expired.
• Inspect and replace damaged O-rings as needed.

What Are the Pros and Cons of the Honda CRF125F?

Pros

• Easy to Work On
• Overall Quite Reliable
• Fuel Injection (newer models)
• Smooth Shifting
• Electric Starter with a Backup Kickstarter
• Easy Handling
• Fun to Ride

Cons

• Poor Idle/Engine Timing
• Won’t Shift into Gear
• Hard to Start
• Suspension Too Soft
• Clutch Slips Too Easily
• Carburetor Problems
• Leaking Fork Seals

What are Some Alternative Models?

What’s the Resale Value of the Honda CRF125F?

Related: 7 Common Problems with the Honda CRF50F (Explained)

Sources:

Crf For Sale – Honda Motorcycles – Cycle Trader               

CRF125F – Big Wheel Dirt Bike – Honda

New 2023 Honda CRF125F Review: Specs / Features + Changes Explained! (hondaprokevin.com)