Looking for the best CRF125F mods or performance parts to make your Honda dirt bike faster or more comfortable? Whether you’re a casual trail rider or want to build a sweet “play bike”, you’ve found the right article.
I’m going to show you why modifying your Honda CRF 125 can actually hurt your dirt bike, why you need to choose the right upgrades, and how to choose the best mods based on your specific needs and budget!
Before you start modifying your dirt bike…
Upgrading to aftermarket parts is cool, but you may find that it doesn’t ride or feel better than when it was stock – in fact, it might feel worse or be more difficult to ride, whether it feels harsh, loose, or have poor throttle response.
It’s easy to add or “forget” to tune a new part/system, which causes it to be worse than before – what a waste, right?! That’s why it pays to do a little bit of research (reading this article) so that you know what mods or upgrades will actually improve your Honda CRF 125 based on your specific needs and riding style.
Where do you ride most?
For example, if you’re a casual trail rider that rides at low speeds, then installing heavy-duty suspension and taller gearing for a higher top speed probably won’t make your CRF125 easier or more comfortable to ride. Instead, you want to focus on tuning for smooth and controllable power with a plush suspension based on your weight, which I’ll cover shortly.
Which generation/year “bike” do you have?
While the Honda CRF125F hasn’t changed much since it was first made in 2014, there are a couple of things you need to keep in mind before ordering aftermarket parts. First, there is a big wheel and a small wheel model, and then there is the carb vs EFI years.
The standard CRF125F has 17/14” wheels and the CRF125FB (big wheel) has 19/16” wheels.
Here are the 2 different “bike” generations by their model year:
- 1st gen (carburetor): 2014 – 2018
- 2nd gen (fuel injection): 2019 – Current
Airbox/Intake mod
Since the CRF125F and 125FB are trail bikes, they’re made to be reliable and durable. This means that the airbox is sealed up very well so that you’re less likely to suck in mud, water, and excessive amounts of dirt.
This keeps the air filter cleaner longer and less likely to suck dirt into the engine, but it also greatly restricts the amount of air going in, which limits your power potential.
So, by simply removing the airbox lid/baffle on top, more air can get to the engine, thus, giving you more potential for torque and horsepower if you tune it properly.
Additional airbox mod
If you want even more air coming in, you can grab a set of Uni airbox vents (Check price on Amazon). They’re an affordable mod and they come with individual filters to help prevent dirt from getting sucked in while allowing more air to get to the carb for more potential power.
Will you need to re-jet after an air box mod?
Depending on how it’s currently tuned, you will most likely need to re-jet the carb or tune the EFI for the best results after opening up the airbox. If you don’t get it properly tuned, you could run into issues, such as:
- Hard starting
- Poor throttle response
- Less power
- Popping/backfire on deceleration
The best place to start tuning a 4 stroke dirt bike carb is with the fuel screw.
Jetting – more benefits than you think
Not only can you get more power from a properly jetted CRF125 carb, but it will also start easier (hot or cold), have a smoother throttle response, and be more reliable because you’re less likely to foul spark plugs or overheat the engine.
Stock jetting:
- Pilot: 38
- Main: 112
- Needle: Non-adjustable
Recommended jetting for 1000 ft. @ 70F deg (uncorked):
- Pilot: 40
- Main: 117.5
- Needle: 2 shims under clip (richens fuel mixture)
- Fuel screw: 1.5 turns out
This jetting chart/guide is a good starting point, but it really depends on your climate and the mods your specific bike has that will determine the jetting. You can buy your own jets for DIY tuning, or you can buy the 6 Sigma jet kit (check price on Amazon) that comes with what you need already that will work for most CRF125’s that are stock or close to stock.
Rebuild stock carb or buy cheap aftermarket carb?
Maybe your CRF125F has bad gas in it from sitting for months or years, causing it to not start or just run poorly. It’s easy to just want to buy a new cheap Amazon carb instead of dealing with troubleshooting or cleaning the original carb, but that might actually require more work.
You see, the reason why these aftermarket “knock-off” carbs are so inexpensive is because they’re poorly made compared to the genuine OEM carb and parts. Simply put, you’re probably going to need to tune the cheap carb as much or more than the OEM when.
So, my recommendation is to give the stock carb a good cleaning and if you need to replace any parts, then a simple rebuild kit (check price on Amazon) is more affordable than buying a new one.
Carb upgrade – is it worth it?
Bigger is not always better – it really depends on what your goals are. If you like the stock power curve of the CRF125F – smooth and predictable, then the stock carb will be your best choice, especially if everything else is stock or close to it.
When is it worth it to upgrade to a bigger carb?
If you’re looking for more top-end power, or you’re increasing the displacement and want more overall power, then it might be time to consider a bigger carb for your CRF 125. When you upgrade one system, then the rest of the bike might be restricting/choking off its power potential.
For example, when you install a bigger carb without changing anything else, there’s too much air for the small engine and exhaust to suck through – this reduces the low-end torque.
But when you increase the engine and exhaust size, the small carb will be limiting the power because it’s not allowing enough air to and through the engine and exhaust – make sense?
CRF150F carb upgrade
Going from the 20mm stock CRF125F carb to the 24mm CRF150F carb if your engine and exhaust are modified or if you want slightly more top-end HP while reducing low-end torque. It’s almost a bolt-on mod (info from TT forum).
The stock intake manifold is ALMOST a direct fit. There is a slight “lip” on the top portion of the intake mouth. About two minutes with a mini file and it will fit.
CRF125F cable won’t fit
The main problem is that the OEM CRF125F throttle cable for the CRF150F carb won’t work. The cable inside is too short, so you need to order a Motion Pro cable that’s 35.25” long with a 90-degree bend at the carb end.
The cable needs to extend 3 7/8″ beyond the threads on the throttle end, or you could just buy the CRF150F throttle assembly (check price on Amazon) when you get the carb.
Suspension upgrade
Once you get your CRF 125 running right, it’s time to address the safety concerns of the stock suspension – especially if you weigh over 150 lbs. The CRF125FB can handle slightly more weight, but both small and big wheel models are trail bikes with soft suspension that are made for kids, teens, and young adults that are just starting out.
That doesn’t mean it can’t be great for experienced trail riders, but the stock forks and shock will be uncomfortable and dangerous if you’re riding fast or aggressively on technical terrain. There are some cheap upgrades as well as expensive and time-consuming mods you can do to your CRF125, depending on your goals and how much you want to invest in it.
Forks – what can be done?
The stock forks will bottom out often if you’re over 150 lbs or ride fast, which will not only feel harsh on your hands, but it can throw you off the bike and damage the forks and/or frame if you repeatedly do it. So, the first thing you should do is get the proper springs for your weight and riding style.
Upgraded fork springs
Heavy duty springs (which I can’t find on Amazon yet, but there are these on eBay), will make your CRF125 front end much stiffer so that it won’t dive as much under braking or bottom out easily. Not only will it be more comfortable to ride, but it will be safer for you and your bike if the stock fork springs are too soft.
The 2nd generation CRF 125 forks changed, so make sure you order the correct springs for your model year. These are the part #s for specific CRF125 models:
- 2013 – 2018 CRF125F big wheel: 650-HCF-1405 (check price on eBay)
- 2019 – Current CRF125F small wheel: 650-HCF-1305 (check price on eBay)
- 2019 – Current CRF125F big wheel: 650-HCF-1205 (check price on eBay)
Two springs too harsh?
Maybe you tried upgrading to the heavy-duty fork springs but now it’s too harsh – it’s too harsh on bumps and shocks your hands, causing you to get fatigued quickly.
There’s a little trick – instead of going back to the stock springs, try one soft and one stiff. This makes it stiffer than stock but softer than both being stiffer.
Cheap “re-valve”
Since the stock CRF forks are very simple compared to modern forks that can be highly modified through a “re-valve”, a cheap way to improve the damping control is by changing the oil weight and height.
You can use a heavier-weight fork oil (check price on Amazon) and raise the oil level so that there’s less air to compress. This makes slows the fork down during compression and rebound when going over bumps and obstacles.
Just make sure you stay within the OEM maximum oil height/air gap specs.
Cheap preload
If you just want to add a little bit more preload to the forks so that they sit up a little bit higher, you can add some PVC spacers under the fork caps on top of the springs. Start with ½” and use washers under and on top of the spacer.
The PVC should be thick (schedule 80) as well as just slightly smaller than the inner fork diameter, as well as the washers so they don’t slide around. You can experiment with different length spacers for more or less preload, but eventually, you’ll need to go to a stiffer spring rate if the preload spacers aren’t doing enough.
Fork emulators
If you want even more performance and don’t mind spending a little bit more time tuning, some Race Tech Gold Valve Emulators (check price on eBay) are the next step up. You are able to tune the valving, which allows you to slow down or speed up the compression and rebound damping, which makes your CRF125 forks feel stiffer or softer.
Fork conversion/swap
A fork swap is not for the faint of heart. The most common 125cc trail bike fork conversion would be installing an 85cc 2-stroke MX bike front end – in this case, a CR85 or even a CRF150R set of forks, clamps, and front wheel.
However, there will most likely be some machining or fab work required to fit the steering stem, clamps, and brake caliper/rotor, depending on which parts you choose.
Other mods to keep in mind when doing a fork swap
For best results, you might need to get different fork springs based on your weight, but not the front end will be much higher, which will cause handling problems. You can raise the forks in the triple clamps so the front end sits lower, but the rear end might still be too low, resulting in a slow-turning bike with less front-end traction.
You’ll either want to raise the rear with preload and/or linkage mods or consider converting the rear shock to another unit with more travel. All of this requires time and planning so you don’t run into issues, especially if you’re the first to try it.
Rear Shock Upgrades
Even though there is no damping adjustment on the stock CRF 125F rear shock, there are a couple of things you can do to improve the performance before upgrading to an aftermarket shock if you’re on a tighter budget. The first thing, like the forks, is to make sure you have the right spring rate.
Correct shock spring for YOU?
The stock shock on the small-wheel and big-wheel Honda 125 is soft if you’re over 150 lbs, so upgrading to a heavy-duty rear shock spring might be necessary, especially if you are making the front end stiffer. Fortunately, it uses the same shock spring as the older XR100 model, so finding one on Amazon won’t be hard (check price).
Do you have the right ride height?
Once you have the correct shock spring, you need to make sure the sag is properly set. The sag (preload) controls the height of the rear end, so if it’s too low or height compared to the front-end, you won’t have as much traction or stability or both – A balanced suspension set up will give you more confidence because you have the most overall traction and control.
Different shock
The two easiest shock options for the CRF125F are:
- Vonkat adjustable (check price on Amazon) – more affordable
- BBR swingarm kit w/Elka shock – best performance
Can you lower the seat height?
Yes, if you like your CRF125F but would like it lower even for just a few rides, you can lower the seat height. One of the easiest ways to lower it is with an aftermarket lowering linkage (check price on Amazon).
It drops the seat height by almost 2 full inches, making it easier to touch the ground, and it’s completely reversible if you want to go back to stock – just swap the OEM linkage link back in.
2 issues with a lowering link that can be resolved
While it can be great to have your CRF 125 lower to the ground, there are two minor drawbacks to using a lowering link. One, is the handling will be changed – it will be slower and harder to turn and slower speeds, but also more stable.
Second, the front end will also be too high compared to the rear, so you’ll want to raise the forks in the clamps so that the suspension is balanced. These issues won’t be very noticeable if you’re a brand new rider and are fairly easy to reverse – just something to keep in mind if you’re considering this CRF 125 mod.
Another fairly easy way to lower the seat height is by shaving the seat foam, but this makes the seat even harder because there’s less foam to sit on – think “wooden 2×4”.
Gearing – cheap performance upgrade
Time to focus on speed and power mods, and this first one is one of the easiest/cheapest! By simply changing the gearing with a different size sprocket, you can make your CRF125F accelerate quicker or have a higher top speed – something that is somewhat lacking due to only having a 4-speed transmission (other 125cc trail bikes have 5 gears).
Better acceleration for off-road
Stock gearing for the CRF125FB (big wheel) is 13/49 and 13/46 for the small wheel, so an easy way to get quicker acceleration is by going up to a 50-tooth rear sprocket (check price on Amazon)
Best Exhaust upgrade
There are quite a few ways to upgrade the stock exhaust on your CRF125F and while you won’t get mega power from this mod, it’s a surprisingly good percentage of gain when properly tuned.
For example, if a new exhaust system adds 0.6 HP, that doesn’t sound like much, but when you go from 6.0 HP to 6.6 HP, that’s a 10% increase with just one part!
Free/cheap CRF125 exhaust mod
The easiest way to uncork your stock exhaust is by removing the baffle/end cap, but there are some drawbacks. You’ll get a lot more noise, and it removes the spark arrestor, so you won’t be legal to ride on state trails.
It’s fairly loud and it looks kind of ugly with the exhaust tip removed, but you can buy a cheap tip (check price on Amazon) with a spark arrestor screen to make it look a little better.
FMF Powercore 4 (‘14-’18)
Want a better-sounding and flowing exhaust? The FMF Powercore 4 system (check price on eBay) is a nice upgrade at a reasonable price.
However, if you live in an area where noise is a concern, the FMF PC4 muffler or complete exhaust is definitely a lot louder than stock – it’s not obnoxious, but not very quiet up close.
BBR D3 (‘19+)
For slightly more, you can get a BBR D3 complete exhaust (check price on eBay) that gives you a little more performance due to the fact that BBR puts a little more time into their development for these trail bike exhaust pipes.
It’s lightweight, and gives you better throttle response and overall power, especially if you tune the ECU. You also get a spark arrestor screen, a wash plug, and a heat shield for the stainless header.
It’s quite a bit louder than stock, so be aware. You can add a quiet core insert (eBay) if you want to keep it closer to stock sound levels.
Pro Circuit T6 (‘19+)
For around the same price, you can also get a quality T-6 complete exhaust from Pro Circuit (check price on eBay). Not only does it look good, but it sounds better, reduces weight, and gives you a little more power.
It’s not quiet, so don’t ride it near neighbors that might complain about the noise. It comes with a removable spark arrestor screen as well.
Yoshimura RS-9 (‘19+)
Yoshimura is the most expensive option on this list, but the RS-9 complete system (check price on Amazon) is also the overall best CRF125 exhaust if you want better power, durability, and sound without being ridiculously loud. It’s still quite a bit louder than stock at high RPM, but at idle and low RPM it’s fairly quiet.
It comes with a spark arrestor and you can buy an optional insert to make it even quieter.
Do you have to re-jet the carb after installing an aftermarket exhaust?
It really depends on how it’s currently jetted, but due to the fact that the 2014-2018 CRF125F carb is jetted lean from the factory, you’ll probably need to adjust to the jetting specs I gave earlier in this article. If you don’t adjust it, it might be harder to start, especially when cold, and the throttle response and power might be worse as well.
Do you need to tune the EFI with an exhaust?
For the 2019 and newer CRF 125 with fuel injection, you might not need to tune it with a fuel tuner – as long as it starts and runs fine and you don’t need more power. However, if it’s hard to start, runs rough, backfires, or you want the most power with your exhaust upgrade, then you’ll need to get a fuel tuner/controller and tune it, which isn’t as hard as it might sound.
Engine upgrades
The CRF125F is far from being a high-performance dirt bike, but there are some performance parts that you can install to make the engine quite a bit more “lively” – it only makes about 9 horsepower at the crank, which is about 7HP at the rear wheel.
Higher compression piston
If you just need to replace the piston and have access to a machinist, a fairly inexpensive way to get a little more power is with a higher compression Wiseco piston kit (check price on eBay). This piston is 1.1mm bigger than the OEM-size piston, so it requires boring and honing the stock cylinder bore.
Increasing compression from 9.0:1 to 10.0:1, and the additional few cc’s of displacement will give you a small boost in torque and horsepower. It’s not huge, but if your piston and cylinder need to be bored over due to scoring, this is a good option.
Big bore kit
One of the best ways to go more power everywhere after tuning the exhaust and intake is with a big bore kit, such as the 140cc kit from Engines Only. More torque, horsepower, and it’s just about as reliable as a stock engine if you properly maintain your bike and don’t hit the rev limiter constantly.
Camshaft
Every little bit counts, and if you truly want to be an awesome CRF125F engine that makes more power everywhere, then you need a good camshaft for your specific setup. The DCR cam will help a stock and modified engine – the bigger the engine, the more low-end torque you’ll feel with this cam.
Head work
One of the last steps to building a high-performance engine, whether it’s a CRF125F trail bike or a motocross bike, is cylinder head work – but most people neglect this important step even though there’s a lot more power potential.
Think about it – if you have a vacuum with a standard-size hose and then you give the vacuum motor 50% more power to suck, it’s not going to suck 50% more because the hose size is restricting it.
Think about it – if the cylinder head intake and exhaust ports aren’t properly sized AND shaped, you’re not getting optimum flow, which can greatly increase torque/throttle response, and horsepower at almost every RPM.
Porting – Warning!
Bigger isn’t always better, especially if you go too big – you can drastically destroy the power curve and lose lots of low-end torque, which is where the CRF125 engine works well. That’s why you need to find a guy that knows what he’s doing with these air-cooled engines when it comes to porting and cylinder head work.
How to make your CRF125F taller
Whether you’re an adult or just outgrowing your Honda 125 trail bike in size, it’s hard to stop riding it because it’s so fun and easy – don’t worry, there are a few ways to make it feel a little bit larger.
After making the suspension stiffer, as listed earlier, starting on the CRF 125FB big wheel is best because it’s over an inch taller.
After that, these are the best mods to make it feel bigger & more comfortable if you’re a taller rider:
- Handlebars (Check price on Amazon)
- Tall seat (check price on eBay)
- Wider footpegs (check price on Amazon)
How to lower your CRF 125
- Lowering link (check price on Amazon)
- Shave the seat
- Lower forks in clamps
CRF125F crash protection mods
If you ride lots of rocks or trails with hard objects that you might hit, then adding some protection can help prevent injuries to you and your bike! Or if you plan on falling often, then your best bet is to learn some safer riding techniques…
These are the top upgrades to keep your CRF125 reliable and protected:
- Hand guards (check price on Amazon)
- Skid plate (check price on Amazon)
- Shift lever (check price on eBay)
- Folding levers (check price on Amazon)
Best Tires for your CRF125F
Best front tire for soft sand/intermediate terrain:
- CRF125F (small wheel): Dunlop Geomax MX33 70/100-17 (check price on Amazon)
- CRF125FB (big wheel): Artrax TG5 Dirt Bike Tire 70/100-19 (check price on Amazon)
Best rear tire for soft sand/intermediate terrain:
- CRF125F (small wheel): Dunlop Geomax MX33 Tire 90/100-14 (check price on Amazon)
- CRF125FB (big wheel): Artrax TG5 Dirt Bike Tire 90/100-16 (check price on Amazon)
Best front tire for rocks/hard terrain:
- CRF125F (small wheel): Dunlop Geomax MX53 Tire 70/100-17 (check price on Amazon)
- CRF125FB (big wheel): Shinko 520 Series Tire 70/100-19 (check price on Amazon)
Best rear tire for rocks/hard terrain:
- CRF125F (small wheel): Dunlop Geomax MX53 Tire 90/100-14 (check price on Amazon)
- CRF125FB (big wheel): Dunlop Geomax MX53 Tire 90/100-16 (check price on Amazon)
Putting all the mods together
Best CRF 125 upgrades for trail riding:
- Carb jetting (‘14-’18 models)
- Intake lid mod
- Suspension upgrade for your weight
Best CRF125F performance parts for racing/pit bike riding:
- Carb jetting/EFI tune
- Intake mods
- Fork upgrade
- Shock upgrade
- Performance exhaust
- Big bore kit
- Camshaft
- Head work
- Lightened flywheel
The best mod to make you a better rider
All of these performance parts, mods, and upgrades will make your CRF125F faster and more comfortable, but there’s one mod that trumps all of them when it comes to your overall control. It starts with your confidence, but just getting more seat time isn’t the best way to get there.
That’s why I made a guide that shows you the most important techniques to work on, and you can download that guide today for free by clicking here.