TTR125 Mikuni VM24 Carb Swap – Best Bang For Your Buck!

Not too often will you see me devote an entire article on a “Make My Dirt Bike Go Faster!” article, let alone on a bike that is meant for beginners. However, there are numerous advantages to this modification on all Yamaha TTR125 models. If you’ve bought a used TTR125 or have owned one for a while, chances are that you’ve had some problems with the stock carburetor, whether it be a bad choke, sticking float/needle, or jetting problems that make it hard to start or not run right.

You can try different pilot and main jets in there, and even fine to the needle position, but it just never seems to run quite right, and it get worse with time. Some parts of it are just poorly designed and they don’t work right after so many years. Fortunately for those of us that like to fix things, these problems can be cured with a better carburetor. Even better yet, a new one can be found for under 100 bucks!

So, why is the Mikuni VM24 round slide carb better than the stock Mikuni on Yamaha’s TTR 125 four stroke dirt bike? First of all, it’s not as finicky and is easier to jet. Once you get the jetting dialed in, you shouldn’t have to mess with anything other than possibly an air screw adjustment in the cooler riding season. Want more power? Because this carb will give you that, even if your TTR is stock. It will make a bigger difference if you have intake, exhaust, and even engine mods (big bore/cam), but with a stock set-up you’ll get better throttle response everywhere and it will rev out much further, making it feel like a different bike.

Junk Stock Carb
Junk Stock Carb

If you’re tired of messing with the dumb bar-mount choke on the TTR, you can throw that out as well with this new carb conversion. The choke is mounted right on the new carb itself. In fact, a lot of owners of this swap say that it usually doesn’t even need the choke to start, even when the engine is cold.

What Do I Need for This Swap?

  • Mikuni VM24/ss carburetor
  • Screwdriver
  • Pliers (needle nose)
  • Drill with 5/16″ drill bit
  • New jets (Depending on where you get the carb)
  • New 6mm Fuel Line (1′ is plenty)
  • File or new clamp?

How Do I Install It?

Technically, I wouldn’t call this a ‘bolt-on’ swap because there are a couple modifications you have to make. However, this is one of the easiest conversion projects you will find when swapping dirt bike parts. Total time should be 1-2 hours if you have everything ready, and even less if you’ve done it before. First thing to do is take off the throttle cap from your new VM24 carb, as well as the one from your stock TTR125 carb and remove the cable/adjustment screw so all you have left are the bare caps. You will be using the stock TTR throttle cable, which will require the metal elbow off of the stock carb cap. It’s held in place with a locking clip, so just pull that out with some pliers.

Now you will need to drill a larger hole on the new VM24 carb cap so the TTR cable/elbow can fit through it. Some people say they used a 1/4 drill, but the TTR elbow fitting measured .285″, which is about 9/32″. That drill might work, otherwise you can go up to a 5/16″ drill (.312″) to make it fit. If you are wondering about the threads, yes they will be gone after you drill through it, but you don’t need the adjustment screw from that cap for it anymore. Now you can put the elbow assembly on the new cap and hook the TTR cable up to the slide.

Some owners of this conversion mentioned that the new carburetor is shorter in length, requiring you to stretch the inlet-side boot to make it reach. I did not have this problem when I swapped it onto my 2000 TTR125L. The clamp on the inlet fits without modification, but the engine side of the carb boot didn’t clamp down far enough on mine. You can either get another clamp, or just file down the spacer in the stock clamp so you can tighten it down more.

After you have the carb bolted in, the only thing left is the gas line. You will more than likely need a longer one to reach the new carb. You can either wrap it around the back of the frame to keep it out of the way, otherwise you can just route it underneath the frame, which is a shorter distance.

If you haven’t already, you can completely remove the stock TTR125 choke and cable because it isn’t needed anymore. Also, for those of you that have the newer model TTR125’s with the two-cable throttle set-up, just use one of those cables with the new VM24 carb and remove or tie up the other one, as it doesn’t use two cables.

New, Better Carb
New, Better Carb

Just turn the gas on now and fire it up! Adjust the idle screw knob when it’s warmed up and it purrs like a mountain lion.

Where Do I Find The VM24 Carburetor?

Fortunately, these carburetors are very easy to find and buy. Not only does Mikuni make a lot of them, but you can also find them off of used dirt bikes for cheap. Sudco and eBay are common places to buy them new. You can also get a VM24 off of a 65cc 2-stroke motocross bike, such as a KX65. They require different jetting, but once they are dialed in, it will run just as well. They pop up on eBay all the time, and can be had for as little as 30 bucks or less. If you’re lucky, you might be able to get away with buying a new jet or two and giving it a good cleaning. If it has a lot of hours, though, it may require a rebuild kit. This isn’t so bad, but it will end up costing almost as much as a new carb. On a side note, I recommend not buying a Chinese knock-off carburetor. They make inferior parts and will more than likely cause problems down the road; just the opposite of what we are trying to do with this swap.

What Jets Should I Use?

Depending on what mods have been done to your bike and where you live, your results may slightly vary. If you’re buying a new Mikuni VM24 from Sudco or from an eBay seller that sells new ones, they come jetted fairly close, although you may need to swap out a jet.

Like I mentioned above, if you’re using a VM24 carb from a 65cc 2-stroke then it will require different jets to run properly. The 65’s need much richer jetting compared to the small-bore four-strokes, so you’ll need to change the main jet for sure, and possibly a pilot, depending on what comes with it.  Don’t worry, jets are only a few bucks, and they share the same jets as most other Mikuni VM and TM carbs.

Below are average starting points for the two different VM24 carbs you can put on your TTR125. These are based off of an elevation of about 1000 feet, and a temperature of 70 degrees Fahrenheit. The engine is stock, but it has an aftermarket exhaust.

New VM-24 From Sudco:

  • Main Jet: 105
  • Pilot Jet: 17.5
  • Needle: 1st or 2nd clip position from top

Used VM24 From KX65:

  • Main Jet: 155
  • Pilot Jet: 27.5
  • Needle: 1st/top clip position
  • Air screw: 1-1.5 turns out

The needle is about the only thing that may be harder to tune. It runs a little rich, especially with a bone stock TTR, even at the leanest position. I haven’t found any leaner needles you can buy for it, but after riding the bike for a little bit and allowing it to fully warm up I didn’t even notice a hesitation. Other than that, this bike runs great now from bottom to top with more over-rev due to the larger bore size.

Was that too much reading to remember? I’ll give you a quick low-down on what this swap entails…

  1. Remove stock TTR carb and throttle cable/elbow
  2. Remove VM24 throttle cap and drill hole up to 5/16″
  3. Install the stock elbow onto the VM24 cap that you just drilled
  4. Adjust your needle clip while it’s out, then hook up the throttle cable and scew on the cap
  5. Install new main and pilot jets if needed
  6. Remove the old choke cable and one of the throttle cables if you have a newer model TTR
  7. Fit the VM24 on (making necessary boot/clamp adjustments if needed)
  8. Route new fuel line onto the carb.
  9. Turn the gas on and fire it up!

If you have any questions or comments, or think like something is missing, feel free to to email me or post a comment on the article below. Good luck, and ride safe!

-Tom Stark

XR100 Vs. TTR125 – Best Beginner Trail Bike?

The Honda XR100/CRF100 and Yamaha TTR125 are among the most popular beginner bikes. Why? Because they are easy to ride, have a clutch, and require very little maintenance compared to a motocross bike. Change the oil and filter regularly, as well as lubing the chain, and these will last virtually forever. So the question is, which one is the better bike?…

There’s No Replacement For Displacement

As you would imagine, the TTR125 has a little more power than the XR100. It has quite a bit of torque for being an air-cooled engine, but nothing that will scare you. The Honda is very smooth and has a linear power-curve, so no surprises there. The flywheels are heavy on both engines, so they are slow to rev and harder to stall, making it great for someone learning how to use the clutch.

2003 TTR125L
2003 TTR125L

Both bikes have a five-speed transmission with about the same ratios, so not much to dispute there. First gears are very low, so you may want to change the gearing (sprockets) once you’re used to riding the dirt bike.

Some people may say the TTR is a bit finicky when it comes to tuning the carburetor. We’ve had a couple of these bikes and the only problem we’ve had is when they sit for months at a time (this happens on any bike when gas is left in it). Just pull the carb off (which is very easy), clean out the jets and passages with compressed air and/or carb cleaner, and we were up and running again!

Suspension – It Is What It Is

Not much to see here, as both dirt bikes are using suspension components that are decades old in technology. This isn’t necessarily bad, especially if you are just a casual trail rider, as it makes these cost very little to buy and maintain. Comparing the two, there’s not a lot of differences in fork and shock set-up. If you weigh over 140 lbs, you’ll want to get heavier springs no matter the kind of riding you’re doing. Jumping is not recommended unless you make some modifications to the frames to strengthen them, but that’s not what these bikes are for. For a younger kid that just wants a dirt bike to ride around and have fun, either is a great choice, as they will teach you all of the controls and skills needed on a motorcycle.

Handling

If you’re brand new to dirt bikes, handling on a dirt bike won’t be as big of a factor as ride-ability and reliability. However, there are some differences between the XR/CRF 100 and TTR 125 as far as handling goes. The Yamaha weighs a little more; particularly if you get the LE model with the larger wheels and Electric start. After riding both bikes, the 2001 and newer Honda feels a little slimmer handles a little better in the tight stuff. The 2000 and older XR100R’s have a wider seat and tank, but are more comfortable on your butt. The TTR front-end isn’t the greatest, as it wants to slide out a little more, but that’s probably because we were pushing it too hard (that’s what happens when you put an adult on a bike like this!).

So Which Bike Would I Buy?

2000 XR100
2000 XR100

Honestly, I would buy either dirt bike if I found a good deal on a clean one, which is the most important thing when looking for a used bike. If I could choose one over the other, it would probably be the Honda. Not because it’s red, but because Honda just knew what they were doing when the built the XR/CRF-F lineup. They’re easier to find, the engine is simple, and aftermarket parts are widely available.

-Tom Stark

CRF50 Vs. PW50 – Best Kids Dirt Bike?

Buying a dirt bike for your kid can be one of the best feelings for both your kid, as well as yourself. Choosing the right one can be a hard decision, but either bike can fit the bill. There’s a few major differences between the Honda CRF50F/XR50R (Same bike, just different body style), and the Yamaha PW50, so lets see what each of them have to offer.

Engine Comparison

CRF50F
CRF50F

For both being 50cc, the engine’s are quite a bit different. The Honda has an air-cooled four-stroke with a three speed semi-automatic transmission, while the Yamaha has a two-stroke, oil-injected engine with a centrifugal-clutch. They are both pretty much bullet-proof as long as you regularly change the oil and keep the air filter clean.

Neither have electric-start, but the Honda engine is a more versatile. In stock form it’s already more powerful and has three gears, making it easier for your kid to get past certain obstacles. The aftermarket has a lot more to offer as well for the CRF/XR 50. It is one of the most popular pit bikes for adults, so there’s plenty of engine, suspension, handelbars, and other hop-up parts available to fit the riders needs.

However, if you want a light and mellow power-band without having to change gears, the Yamaha is a great starting point. It also has a throttle-lock feature that you can set to lock the throttle at a certain position so that your kid doesn’t hold it wide open and get into trouble as easily.

Suspension

Neither have that good of suspension from the factory. The CRF50 is going to be a little better, but still isn’t good enough for racing on. Of course, these are just kids dirt bikes for beginning riders, so they are plenty good for trail and play riding. The Honda once again has plenty of aftermarket options for forks, shocks, and swing-arms if you are willing to shell out the dough though.

PW50
PW50

Size

Size may be the most important factor, depending on how small your little boy or girl is. If you’re looking for the lowest seat height and lightest bike, the PW50 has the CRF beat. Its seat height is only 19 inches, and weighs a shocking 86 pounds when wet with fluids. This is substantially lower than the 110 lbs of the Honda.

In The End…

It depends on the nature of your kid. If your boy or girl is small and barely knows how to ride a bike, the PW50 is probably the better choice, due to it being smaller, lighter, and smooth on power. However, almost all kids grow out of the PW’s within the first year, so there’s a good chance you’ll be needing another bike soon after. Whereas the Honda will last a little longer since it’s a little more powerful, has a 3-speed transmission, and plenty of aftermarket parts for upgrading. You can usually get a couple years out of the ol’ Honda 50 before needing a bigger dirt bike, depending on how fast your kid grows and learns.

What’s Hot?

Honda:

  • Bullet-proof 4-stroke engine
  • 3-speed semi-auto trans.
  • More versatile
  • Plethora of aftermarket parts
  • It’s red

Yamaha:

  • Mellow 2-stroke engine w/ simple oil-injection
  • Low seat height and light-weight
  • Low maintenance engine and shaft drive
  • It’s blue…?

Hopefully this will give you a better idea on which little dirt bike to buy for your kid to get into this awesome sport. Feel free to leave a comment or question. Have fun, and remember to wear proper safety gear!

-Tom Stark

Yamaha YZ125 Review – Is It The Best 125 Two-Stroke Ever?

Since there’s not much hope in the economy coming back in the near future, dirt bikers are resorting to things that will give them the best bang for their buck. As a result, 125cc two-strokes have been rising in the used market. Why? Well, it’s pretty simple, actually. First of all, you can rebuild the top-end for $150 or less, which can be done in your garage with a little mechanical motivation and patience. They are great dirt bikes to start out on for motocross, as they teach you how to control the throttle, clutch, and controls. Probably the best part about a 125 2-smoker is that they’re an absolute blast to ride! They’re light, quick, snappy, and besides, who doesn’t like the smell of race gas and pre-mix in the morning?!

Which Decade?

Yamaha hasn’t changed their 2-strokes for a while. However, this doesn’t mean it’s outdated. In fact, that’s quite the opposite, as Yamaha has been building quality 2-stroke motocross bikes for years. As long as they make them, riders continue buy them. They are often the first dirt bikes to sell in a dealer, but let’s take a look at why these bikes are so popular in the first place.

1990’s YZ two-strokes are fairly similar. In ’96 they made some changes that lasted until the end of 2001. These are still considered some of the best motocross bikes, especially the 1999 model. They are fast, reliable, and are just a great overall bike.

In 2002 the frame changed, making it lighter, narrower, and more flick-able. However, many people didn’t approve because it switched to a 5-speed transmission. 125’s have a narrow power-band as it is, and some riders just like having that extra gear.

2005 and 2006 are biggest years for the Yamaha YZ125. In ’05 they changed to an all aluminum frame, made some engine changes, as well as changing back to a 6-speed transmission.

2006 Yamaha YZ125
2006 Yamaha YZ125

Power

Power has never really been an issue when it comes to the YZ125. In amateur ranks, these small-bore two-strokes can hold their own against 450’s with the right rider. Of course it can be harder to ride them faster, but they have the ability, and it’s extremely fun doing it. Although 125’s are known to have little to no bottom-end power, the YZ125 has always seemed to have a little more torque down low than the others in its class, making it manageable if you need to lug it in tight areas. Once you get to the mid-range you can start to feel the inner-beast come alive, especially on the later models. As soon as you hit the power-band on one of these tiddlers, you’ll know why they are so addicting. It may scare you at first if you’ve never ridden a two-stroke motocross bike, but you’ll be begging to do it again and again until there’s no more premix in the tank… Throw a pipe on this thing and get it properly ported, and you have race-ready engine on your hands (not that it isn’t with a stock engine).

In 2005, the YZ125 got a new engine and carburetor, which greatly improved the bike. It’s so crisp and fast that you don’t need to touch the bike to be competitive. Although, as the saying goes, it’s easier to make a fast bike faster… Slap a pipe on there, get it ported, run some race-gas, re-jet, and she’s ready to haul the mail!

Handling

While it’s light, fast, and flick-able, some people don’t like the way YZ125’s handle as much as other late-model 125’s. The CR125 has been at the top of its class in the handling department since the 3rd generation chassis came out in 2002. That bike handles extremely well with comfort. The 2002 and newer YZ125 are not far behind though, so don’t let that be the determining factor.

2005 was the first year of the aluminum frame, which is still claimed to be one of, if not the best 125 two-stroke made. It’s lighter, faster, handles better, and just overall rides more like a modern motocross bike.

Suspension

Yamaha continues to provide top-notch suspension in their motocross bikes, and the YZ125 is no different. The older bikes from the 90s left something to be desired compared to modern mx bikes, but in the 2000’s they have some of the best suspension out of the box. Bottoming-resistance is one of the leading factors of it being at the top of its class. The ride isn’t as harsh as some of the other bikes, but like any other motocross bike, you will want to get it re-valved if you weight less than 140lbs or more more than 170lbs depending on what kind of riding you do.

In 2006, which was the last year of any major updates, the YZ125 received new SSS forks, which are considered a big upgrade. If you can find a good deal on clean ’06, buy it! If you find a nice ’05, I would definitely buy that too. For someone that’s not a pro rider, you probably won’t notice much of a difference between the two. Besides, most racers get their suspension re-valved for their weight and riding style anyway.

You Should Get A YZ125 If You:

  1. Want a light, nimble, quick bike
  2. Like mixing gas and the smell of premix
  3. Want to go back and learn the basics
  4. Like snappy power
  5. Want a dirt bike that’s cheap to maintain
  6. Want to rub it in when you beat friends on four-strokes
  7. Don’t want to make the jump all the way to a 250F
  8. Want to rebuild top-ends at home

You Shouldn’t Get A YZ125 If You:

  1. Don’t like mixing gas or the smell of premix
  2. Want a smooth and very predictable power-curve
  3. Like checking valve clearances
2001 Yamaha YZ125 2-Stroke
2001 Yamaha YZ125 2-Stroke

I’ve owned my share of YZ125’s, and they’ve all been great. The most reliable motocross bikes I’ve owned, and they’re just so much fun to ride. Of course, the newer the better, but even a 1999 YZ125 is a great bike to get started in this awesome sport. Check out my other articles on how to find deals on used dirt bikes!

-Tom Stark

 

YZ125 vs. YZ250F – The Trillion Dollar Match-Up


Does the monster torque of the YZ250F make it that much better than the light and snappy YZ125? (I would have said million dollar, but that’s inaccurate since that would be like pocket change here in the U.S.) We have to dig a little deeper than what the media and government says. I think we all know that most motocross companies are pushing for the four-strokes because they are “eco-friendly” by not producing as much pollution as the two-strokes, as well as costing much more to repair because there are twice as many parts that can break. But for this battle we will totally scratch those opinionated facts out because they don’t mean a thing in the motocross realm.

I have ridden Yamaha’s YZ250F’s and YZ125’s, and can say that they are two different kind of animals. Both Yamaha motocross bikes have plenty of power and will require some balls to ride fast, but are about as reliable as you can get as far as motocross bikes go. Each bike has its ups and downs, but the question is, “which one is better overall?” Well you’ll have to wait until the next article after I do a little more research on these bikes……. Just kidding.

YZ125

Ahhh, the smell of pre-mix in the morning! Are two-strokes making a come-back? Well, I’ll cover that in a future article… The YZ125 is a serious piece of art. It’s been rated the number 125cc motocross bike in magazines and websites more than any other 125 two-stroke. The light-weight makes it flick-able, the raw horsepower begs it to be revved to the moon, and the suspension is top notch. There’s no question that this bike is ready to race right out of the box. Although you might have to re-jet the carburetor if you are riding in an extreme climate.

How Does It Handle?

Pretty much any modern 125 two-stroke is going to handle well these days, and the YZ is no exception. The handling is among the best in its class. It will ride any berm and the front end will stick pretty well in those pesky ruts. What I like about the 125 is that it has a really low center of gravity compared to the four-stroke, so it made it a lot easier to lay in down in the corners. I am a shorter rider (5’6”), so having a bike that handles well in corners is a must. The YZ125 felt comfortable to ride and cockpit was narrow while the 250F was a little more bulky.

What’s The Suspension Like?

You want good suspension? You got it! The YZ125 suspension set-up is great right off the showroom floor. If you weigh more than 180 or less than 140 lbs then you might want to consider getting some softer fork and shock Springs though. The stock suspension has really good bottoming resistance and can handle a lot. It feels great on any kind of obstacle. Although it may be a little mushy for A or pro riders. The forks soaked up most of the braking bumps and the bike was very controllable in the air and in the corners. It felt stable at all speeds.

What About the Engine?

The engine may be the two-strokes’ greatest set-back against the 250f, but it is no slouch. Any skilled rider will be competitive on this little ripper. The YZ125 may not have the torque that the 250F does, but it has the horsepower to make up for it. Yamaha’s 125 is known for it’s do-it-all engine. It does have more bottom-end power than any other 125 two-stroke I’ve ridden. The mid-range has some punch, and the top-end is never-ending fun. All you have to do is keep this bike on the pipe then you will be able to pass those 250F’s, that’s it.

Additional Notes…

Above are the main topics that riders ask about when deciding which bike to get. I just wanted to give you a few more facts about this bike that could factor into your decision. The YZ125 is a great motocross bike to start out on, and is perfect for younger riders just stepping up from and 85 that don’t want a big four-stroke. This bike is cheaper and easier to maintain. The cost to rebuild any 125 will be less expensive than a 250F just because it’s a two-stroke and has less moving internal parts. That doesn’t mean you will be spending less, because if you don’t maintain it, it will break down eventually. The YZ125 has always been very easy to start. If it’s not, then you have a problem. One of the only extra things you have to do to this bike is add pre-mix to the gas before you put it in the tank and ride.

YZ250F

It’s bigger… It’s badder… Is it too much for the two-smoker to handle??? The YZ250F has been the top selling 250cc four-stroke motocross bike. Is there a reason for this? There must be, so let’s check it out!

Does It Handle As Well?

A simple question, and it will be responded with a simple answer… “no.” You can do anything you want to the bike, such as lowering the radiators, reducing the weight, or shaving the seat, but it’s never going to handle as well as the two-stroke unless you do major modifications. That does not mean it handles poorly. Over the years Yamaha has turned their YZ250F tank into one of the best handling four-stroke dirt bikes. The newer the model, the better it gets. The main difference between this bike and the 125 is that it’s top-heavy, meaning the center of gravity is at a higher location on the bike, causing it to be less stable. This is most noticed in the corners, so laying it down will be a little more difficult for shorter or younger riders.

How About Suspension?

Suspension on the 250F is great for 140-175 lb amateurs, similar to the 125. It has good bottoming resistance and handled jumps with ease. Not much else to say except that the suspension on the YZ250F’s worked well for me.

Does The Engine Make Up For It?

The first time I rode a YZ250F I was blown away. Torque across the entire rev-range was unbelievable. This bike gives you the traction and power down low that you will never get from the 125. The “power-band” is not as fun as the two-stroke. The torque, though, will pull any 2-stroke out of corners. After riding a 250F for a while, the smooth, yet powerful engine just got a little…… I don’t know if I should say it…. boring. It just wasn’t as fun to ride around on as the two-stroke. Racing the YZ250F would be a different story. It’s not exactly about riding whichever bike is more fun, it’s about riding faster and more comfortably than the other riders. This bike helps out a lot on that part, but is it good enough to beat the 125?

Notes:

The YZ250F was the first four-stroke motocross bike in the 125 class, and has been the most reliable 250F the entire time. Take care of it and it will take care of you. The first years, 2001 & 2002, the bike had manual-decompression, making it a little more difficult and time-consuming to start. That can be fixed with an ’03 or newer exhaust cam because Yamaha switched to auto-decompression. The YZF250 is probably the easiest 250F to kick start. I was usually able to start mine in 1-2 kicks when they were cold.

The bad part about owning a 250F is that it can grenade if you don’t maintain it properly. If it does just “happen” to blow up, the cost of repairs can be enormous, especially if you have a shop to do it. This is one of the only reasons why I don’t like the four-stroke motocross bikes, otherwise I would buy more of them.

And The Winner Is….

Neither bike, because they are just as good as each other…… You didn’t want to hear that, did you? Good, because it’s not true! After comparing the characteristics of these bikes that have been rivaling each other for the past decade, there are still pros and cons that each bikes has. My decision would be to go with the YZ125 because I love two-strokes and don’t like big bills when they explode. For a racing scenario where money is no option and the only goal was to win then I will choose the YZ250F. It has the torque and horsepower that will beat the 125 on almost any track, the suspension is great for me out of the box, and it’s just plain easier to ride faster. That’s why the Yamaha YZ250F is still the better bike in most cases for this match-up.

Furthermore, there are so many variables to consider because not every rider is the same and rides similar terrain. If you have a big bank and want to be on par by technology standards then the 250F is the bike for you. If listening to a two-stroke WOT is music to your hears, and you want to learn better riding techniques as well as a bike that’s easier to maintain then a YZ125 is a perfect bike.

Remember… whatever bike you choose, have fun and ride hard! Good luck!

-Tom Stark