Best TTR 125 Mods That Are ACTUALLY Worth Your Money

Cheap/Free Re-Valve?!

Instead, to get a stiffer, yet more plush fork action to help get rid of that pogo-stick ride, you can use one stiffer fork spring and heavier-weight fork oil (Amazon). That's right, one stiffer spring and one stock spring will still increase the spring rate over stock, and the heavier fork oil will help with the damping.

A heavier oil will slow the damping/compression of the fork down as you go over objects. It's kind of like the poor man's re-valve.

More easy ways to tune the stock forks

You can also tune the oil level (air gap in the forks) to help with bottoming resistance. Just remember to stay within the recommended factory tolerances or else you risk doing damage or blowing seals with too little or too much oil in the fork.

To save even more money, synthetic motor oil can be used as a fork oil substitute. I have personally used it in some of my forks as per the recommendation of Bruce Triplett, the old-school suspension guru.

Rear shock upgrades

Much like the stock fork, a stiffer spring can be used to accommodate a heavier or more aggressive rider. A new shock spring (check price on Amazon) is around the same price as fork springs.

"E" model shock upgrade

The next expensive mod would be to swap the stock shock with one from a TTR125LE model if you have a standard or 125L model. The 125LE shock has a remote reservoir and is adjustable. You can rebuild it or send it to a professional to get it re-valved for your weight and riding style.

Adjustable aftermarket rear shock

If you want a simple way to get a lot better rear shock performance and have a larger budget, the Vonkat adjustable rear shock (check price on Amazon) is a great upgrade over the stock shock. Not only can it handle adult riders, but it absorbs bumps and obstacles better to give you more comfort & confidence.

The major benefits of this shock are:

• High-quality seals and fluid - better durability, allowing you to ride longer with less shock rebuilds
• 14mm shock shaft - increased durability and stability compared to the 12.5mm stock shock
• Air adjustable spring assist - increase the air pressure to make it stiffer/softer for greater tunability
• 18-click rebound damping adjustment - increase traction and comfort by tuning how fast the shock rebounds based on your weight & riding style
• Rebuildable - allows you to keep using the shock for many years because you can replace parts when needed (stock shock is NOT rebuildable)
• Clevis made from 6061 aluminum - much lighter than stock while still being strong/durable

TTR 125 Suspension conversion kit

Maybe you've seen people with a TTR 125 that has front forks and a rear shock from a different bike, such as the YZ85 motocross bike. Unfortunately, there's no aftermarket suspension conversion kit that you can actually buy.

You have to buy the forks and do the mods yourself. This involves fitting the complete front end and then potentially doing some slight mods to make it fit properly and then getting the front and rear suspension balanced so that it handles well.

Don't Snap Your Frame In Half

A frame cradle is extra support to the frame of your TTR125. If you are a heavier rider that surpasses the OEM weight capacity, you risk bending or cracking your frame. This is especially true if you ride aggressively.

A broken frame while riding could not only result in costly repairs but there's a significant risk of injury if the damage is severe enough to cause you to wreck.

I have a BBR frame cradle (Amazon) on both of my TTR125's. It's just cheap insurance if you're going to ride them hard.

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Best cheap & free TTR125 Intake Mods

Before doing any mods to make your TTR more powerful, you need to learn how to properly tune a carburetor. Jetting a carb may sound intimidating to you if you haven't done it before, but it's not as complicated as you might think.
You can get started in just a few minutes to make your bike easier to start and have more power.

The TTR125 is usually pretty lean from the factory, so any intake or exhaust mods you do will probably make that lean condition worse. Lean jetting will make the bike harder to start, not run as smoothly, and often pop/backfire on deceleration.

A TTR125 usually runs lean from the factory. If it's hard to start, pops or crackles on deceleration or takes a long time to warm up, this is probably because you need to go larger on the pilot jet.

Free Air Box Mod

Opening the airbox can increase airflow and give the engine more power potential, but that doesn't mean a stock TTR125 automatically needs as much airflow as possible.

Intake modifications make more sense when the carb, exhaust or engine has also been modified enough to use the additional air.

And any meaningful increase in airflow requires checking the jetting. A TTR125 is already commonly lean from the factory, so opening the intake without adding enough fuel can make starting and throttle response worse rather than better.

Upgraded air filter for better throttle response

The stock air filter works, but it does limit how much air can get into the engine, which will limit your power potential - especially if the engine or exhaust is upgraded!

Upgrading to a BBR free-flow air filter kit (check price on Amazon) is a good way to get the most performance out of your stock intake without changing to an unreliable pod filter. It's on the expensive side for a filter, but it's a high-quality product that works.

More Air + More Fuel = More Power

If you want even more air you can drill or cut 1" diameter holes in your air box and cover the inside of them with some Uni filtered air vents (Amazon) to help keep dirt out. Just remember that the more holes/area you have open in your air box, the more dirt and dust can enter in.

This is why it's important to have a good, clean air filter that can keep more dirt out of your engine while allowing more air in. Or there's always upgrading to a carb that will automatically give you more air and power when properly jetted...

Easy Carb Swap Better In Every Way??

The stock TTR125 carb is lacking, to put it lightly. The choke knob can be nice to have on the handlebars, but it's not reliable long-term. The stock carb gets dirty internally and the passages gum up easily because they are so small.

A dirty carb also makes it very difficult to start the engine, whether it's kick-start or electric start. The stock carb is also very lackluster in throttle response and power.

Upgrading to a Mikunki VM24 carb (pre-jetted on Amazon) is a fairly simple conversion if you like DIY projects. The VM24 carb, when properly jetted, will make your TTR125 start easier, have a better throttle response, and provide more power, especially with supporting exhaust and engine mods.

Want better throttle response than the stock carb can provide?

I've personally done the Mikuni VM24 conversion and put together the complete installation, jetting and riding results.

Next: TTR125 Mikuni VM24 Carb Swap — Is It Worth It? →

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TTR125 Gearing — Don't Automatically Gear It Taller

he stock TTR125 gearing is actually pretty good for a stock trail bike, especially for a beginner. The low first gear makes it easier to start, ride slowly and learn clutch control.

Taller gearing can reduce how often you have to shift and give you more speed in each gear, but going too tall on a stock engine can make the bike feel slower because it has a harder time pulling through the low and mid RPM range.

Once you've added more torque with a properly tuned carb, intake/exhaust or engine modifications, taller gearing starts making more sense because the engine can pull the taller ratio more easily.

So I wouldn't change gearing just because you want more top speed. Match it to your engine output and the terrain you actually ride.

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Handlebars & Controls for Adult Riders

The stock TTR125 handlebars work, but they're fairly low and easy to bend compared with a quality aftermarket aluminum bar.

For a taller adult, a slightly taller bar with the right bend can make the cockpit more comfortable both sitting and standing.

But don't automatically install the tallest bars you can find.

Handlebar height and bend affect your body position, which affects front-wheel traction and handling. Bars that are too tall can make it harder to get your weight forward when cornering.

I'd choose a stronger bar with a bend that fits your height and riding position rather than simply trying to make the TTR125 feel like a larger motorcycle.

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Best TTR 125 Tires for traction

Everyone knows you need tires sooner or later, but this is a more important mod or upgrade than you might think. Having fresh rubber on your TT125 (check price on Amazon) will make a huge difference in handling if your tires are worn or over a year old!

New tires can instantly improve a TTR125 if the existing rubber is worn or hardened—but the right type of tire matters just as much.

• Soft-terrain tire: sand, mud and loose/soft dirt
• Hard-terrain tire: hardpack and rocky terrain
• Intermediate tire: best compromise if you ride a mixture

Don't assume the most aggressive-looking tire is automatically best. Choose the tread and rubber compound for where you actually ride.

A rear tire will slow you down from a lack of traction, but a bald or hard front tire can easily lose traction and cause the front end to wash out. These are the kind of accidents that have you on your face so fast that you'll be wondering what in the world happened! Yes, speaking from experience here...

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Is a TTR125 Exhaust Worth It?

I wouldn't make an exhaust one of my first mods on a stock TTR125.

The stock exhaust works pretty well with the stock engine. An aftermarket exhaust makes more sense once you've upgraded the carb and/or engine and need additional exhaust flow to take advantage of the extra power.

It will also make the bike louder, and depending on the muffler or end cap, you may lose the spark arrestor required for some public trail systems.

If your TTR125 is otherwise stock, I'd spend money on suspension, proper jetting, tires or controls before buying an exhaust.

Cheap exhaust tip - will it help?

You can remove the stock end cap and baffle from your TTR125, but it's going to be a lot louder and it might even make less power - especially if you don't change the jetting.

If you're on a tight budget but want better/more sound from your TTR with a slightly better throttle response, install a CNC billet aluminum exhaust tip (check price on Amazon) that quickly replaces the stock tip/cap on the stock muffler. The biggest drawback is that it doesn't have a spark arrestor, so it's technically not legal for riding on state trails.

Best complete exhaust upgrade for your TTR125

A complete exhaust system will give you better performance when it comes to torque and horsepower. The full FMF Powercore 4 System (MotoSport) is almost as cheap as just the slip-on, but it makes more power because the head pipe is larger and flows better.

It's definitely louder than stock, but the sound level is not obnoxious. Just be aware in case you ride in a noise-conscience area.

Do you need to adjust carb jetting with an exhaust upgrade?

In most cases, yes, you will need to adjust one or more of the jet circuits. Exhaust upgrades will work best if you properly tune the jetting because they change the air-fuel ratio.

If your jetting was tuned properly with the stock exhaust, then changing the pipe or muffler will change the jetting, causing it to run worse. It may be harder to start, have less power, poor throttle response, and be less reliable in the long run until you spend a few minutes tuning it.

Want to tune your TTR125 instead of guessing at jets?

My free 4-Stroke Fuel Screw Tuning Guide shows you how to use your bike's response to determine whether the pilot circuit is rich or lean—and whether the pilot jet needs changing.

Get the Free 4-Stroke Fuel Screw Guide →

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TTR 125 Engine performance upgrades

The engine is the life source for making your dirt bike go fast and can make the biggest difference in adding more power, but just because you spend 300 bucks on one part doesn't mean it will make a noticeable difference. More on this later.

I just want to remind you that if you don't tune the carburetor jetting accordingly, you might not see the gains that you are expecting.

How Far Should You Modify the TTR125 Engine?

Stage 1: properly tuned stock carb
Stage 2: VM24 + appropriate intake/exhaust
Stage 3: big bore
Stage 4: cam + properly ported head

A big bore primarily gives you more displacement and torque. If you want to take advantage of that extra displacement at higher RPM, a properly selected camshaft and cylinder-head work can increase airflow and power further.

But these parts need to work together. Installing the biggest carb, cam or exhaust you can find doesn't automatically create the best engine.

Big Bore Kit - are they worth it?

A big bore kit is one of the easiest ways to get more power out of your TTR125 because it's turning it into a bigger engine. If you're looking for a noticeable increase in power, a quality big bore kit is definitely worth it - especially if your TTR 125 top end needs to be rebuilt.

Increasing the engine bore size with a bigger piston alone will give you more bottom-end and mid-range power. More on this later.

Big bore kit vs stock - installation & reliability

It can be just as reliable as stock, if not more so! The biggest factors are: using good-quality parts and correctly installing them, as well as properly warming your engine up.

As far as installation goes, it's the same as using OEM parts. If you can rebuild the top end on your stock TTR125 engine, then you can easily install a big bore kit - I highly recommend picking up an OEM service manual if you want step-by-step instructions.

BBR Kit - Don't buy it without knowing this!

With the BBR 150cc big bore kit (Amazon), you'll get a nice boost in low-end and midrange torque after tuning the carb jetting. This kit fits all years because the TTR125 engine hasn't changed.

If you decide to go with the BBR kit to get more power, make sure you check the threads for the timing chain tensioner. They have been known to have quality issues that cause the bolts to strip out.

If you happen to get one with bad threads, contact the seller, or re-drill and tap the holes for the next size larger bolt. Other than that, the BBR kit will have all of the proper tolerances to give your bike a well-performing and long-lasting engine.

Cheap big bore kits - are they worth it?

There's a selection of options now that you can choose from to get a bigger bore for your TTR125, some are worse than others.

A cheap off-brand big bore kit (Amazon) complete with cylinder and piston parts may work, but the tolerances and quality of material and work just don't compare to most name-brand components. The performance might be lower, and the reliability will be less.

Will you need to re-jet with a big bore kit?

In most cases, yes, you will need to adjust the jetting because the engine is pulling in more fuel. You'll most likely need to go leaner on the fuel screw and pilot jet, as well as the needle clip position.

Camshaft - how it affects horsepower

The camshaft can make the biggest impact on what the power curve of your engine runs like. The stock cam in your TTR 125 is very conservative - low lift and low duration.

It produces smooth power and you'll never have clearance issues with the stock internal engine parts, but it leaves a lot on the table when it comes to torque & horsepower.

Where Do You Want The Power?

When swapping cams, you can buy one that shifts the power for more mid to upper RPM power, or lower to mid for more grunt. It depends on the selection of aftermarket availability and what kind of riding you do.

For example, if you want a broad power curve that's best for trail riding and overall power, then you should get a Stage 1 Hot Cam (Amazon). The camshaft that comes in the BBR big bore kit is not much better than stock. Upgrading to a Hot Cams or Web Cams camshaft will give you even more performance.

Clutch upgrade - is it actually needed?

Another weak link on the TTR is the stock clutch. If you weigh over 100 lbs and ride at moderate to aggressive speeds you will wear out the clutch fibers because they were not built for that kind of abuse.

Signs of Weak/Worn Clutch

When there's less distance to engagement in the clutch lever, the clutch engages really quickly (as far as lever movement goes), or there's clutch slippage under heavy acceleration are all signs that your clutch is wearing and should be adjusted or replaced soon.

Free/Cheap Clutch Mod

To fix the weak clutch, you can install stiffer clutch springs, or you can add a washer under each clutch spring, so you will have to remove the case cover and take out the bolts and springs holding the clutch basket in.

Adding washers/shims that are .030" thick (.75mm) will increase the preload on the springs, therefore making the clutch stiffer to prevent slippage.

It may make the clutch lever slightly harder to pull, but the trade-off is worth it if you plan to put a lot of hours into your TTR125.

Head Porting - Not All Porting Is Created Equal

Cylinder head porting is often an afterthought because many riders don't have the time or motivation to send it out to someone.
They would rather spend $300 on an exhaust than on porting because it makes the biggest noticeable difference (sound) and is easy to bolt on, but the intake and exhaust ports are choking your power potential.

If You Are Serious About More Power

If you actually want to get the most out of your TTR125, or any 4-stroke for that matter, you will come to find out that porting done right is the missing link to making a great running engine.

Stock heads are meant to flow enough air for the stock carb, stock cam, valves, piston, and exhaust... So if you go bigger with those parts, the intake and exhaust ports are just going to choke it down and limit the gains.

Think of it as trying to suck a glass of water up with a regular-sized straw. Now try doing it with a mini-sized straw. It's much harder to draw out the liquid/air when the hole size is choked down.

Lighten Your Flywheel

A lightened flywheel doesn't increase power, but it does make your TTR125 rev up quicker. However, it does have its drawbacks. Here's a quick comparison of a light vs heavy flywheel weight:

Pros of Lighter Flywheel

• Revs quicker
• Faster acceleration
• Quicker throttle response
• Less engine/rotating weight

Pros of Heavier Flywheel

• More stall-resistant
• Rolls over obstacles easier
• Helps prevent wheelspin which equals more traction.

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Which TTR125 Mods Should You Do? 3 Builds I'd Choose

Beginner / Casual Trail Rider

Proper jetting → fresh terrain-appropriate tires → controls/handlebars if needed → leave the engine mostly stock.

The low gearing and smooth stock engine are advantages for learning.

Adult Trail Rider

Suspension → frame cradle → proper jetting/VM24 → handlebars → tires → gearing as needed.

This is probably the sweet spot for most adult TTR125 owners.

Performance TTR125 Build

Proper suspension → frame cradle → VM24 carb → intake/exhaust → big bore → cam/head work → gearing matched to the added torque.

Notice that I put suspension before horsepower on an adult performance build. There's little benefit to making the TTR125 faster if the chassis can't comfortably handle your weight and speed.

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What Should You Do Next?

If your TTR125 is mostly stock, start by fixing the limitation you notice most rather than buying every part on this list.

Want better engine performance? Start with my firsthand TTR125 VM24 carb conversion guide →

Are you an adult who's simply outgrowing the TTR125? Before spending thousands modifying it, compare the best 4-stroke trail bikes for different riders →

The TTR125 can be an incredibly fun adult play/trail bike when it's set up properly—but there's a point where buying a larger bike makes more sense than trying to turn a TTR125 into one.