Common TTR 125 Problems & How To Fix These Issues

Wondering what the most common TTR 125 problems are or just need to quickly fix your bike? Whether you’re looking to buy this Yamaha dirt bike or need help getting yours running again, you’re in the right place!

In this article I’ll show you the most probable issues that show up on the Yamaha TTR125 models, what causes them, and how to fix the root cause. 

This goes for any model, whether you have the small or big wheel, kick start or electric start TTR 125. 

Transmission shifting problems

TTR 125’s don’t normally have transmission issues unless they were in an accident or poorly maintained. Maybe it’s hard to shift or difficult to find neutral. 

Hard to shift

Hard to shift could be from a number of reasons. The most common reasons for your TTR125 being hard to shift are:

• Dirty or low engine oil
• Worn out clutch
• Shift lever loose/bent
• Bent shift shaft 
• Worn transmission parts
• Clutch cable not properly adjusted

The first thing I’d check is the engine oil. If it’s low, add some or replace it, especially if it’s dirty (black). 

A shift lever that’s loose or bent will make it harder to shift because you won’t get the full “throw” or movement to be able to shift it well. 

If you fall and accidentally hit the shift lever, this can bend the shift shaft and cause shifting problems. It’s not likely, but still a possibility. 

Hard to find neutral

Worn clutch plates or basket can make it notchy, grabby, or slip, making it harder to shift. Removing the clutch cover and inspecting the basket and plates will tell you if they need to be replaced. 

Make sure you’re clutch cable is properly adjusted. If there’s too much slack, you won’t be able to fully disengage the clutch, making it drag and be hard to shift into neutral. 

Starting

TTR125 won’t start? There’s a variety of causes, but you need to think of what you did to it last. Sometimes just working on your dirt bike can cause problems, even if you’re trying to be careful. 

The most common reasons why your Yamaha TTR won’t start is:

• Gas or choke is off
• Not enough gas
• Carb is dirty/old gas
• Jetting is off
• Not getting enough air
• Low compression

Hard cold start

You need a richer air-fuel jetting mixture when starting a cold engine. If you’re not getting enough fuel then the carb or pilot is usually plugged or too small. 

Also make sure that the choke is properly working. Once the engine is running, turn the choke off and on – if the engine RPM doesn’t change then the choke isn’t working. 

Won’t Idle

If the engine won’t stay running, it’s often a similar problem to not starting. Make sure the choke is working to keep the engine running while it warms up. 

You can turn the idle screw in to raise the idle RPM so that it stays running. If that doesn’t work then the pilot jet is probably dirty. 

You can try riding your bike for a while and it might clear out and start idling again otherwise you might just need to clean the carb and jets. 

Carb/carburetor

Since the jets are so small on the TTR125 carburetor, they will get dirty and clog up more quickly. The choke mechanism can also fail. 

This leads to frustration because it’s hard to start when cold if the choke doesn’t work. A new carb may be needed, or an upgrade may be better. 

Replacing the stock carburetor with a mikuni VM24 carb is a common upgrade for the TTR125 – I’ve done it with success on multiple TTR’s.  

Flooding

If the carb/engine is flooding with too much gas, then the float needle is either stuck, the float level is too high, or the jetting is too rich. 

You can drain the carb and then hold the throttle wide open to start it quicker/more easily, but the issue still needs to be addressed or it will continue to flood. 

Starter

If your TTR125  has an electric start and it’s not starting then there’s a problem with the battery or starter. If you hear “clicking” then the battery is dead and needs to be charged or replaced. 

A bad starter is not a common issue on this trail dirt bike, but can still happen. The starter motor/gears might get worn out.

If that’s the case, then you’ll need to replace it. At least this bike has a kickstarter for backup. 

Kick start

If the kick start isn’t working, then you might have a bigger problem in the engine case. It could be a broken tooth on the kickstarter gear.

This is another rare issue, but can show up as the kick start lever “slipping” when you kick it down while starting it. 

How to make your dirt bike more reliable

Want to prevent a major breakdown on the trail so that you don’t get stranded or have a bad accident? I want to give you a free 3 step guide to make your TTR125 more reliable. Click here to download it now.