My Dirt Bike Won’t Run – Diagnosing A No-Start

Any day your dirt bike won’t start is a bad day. The problem could be as simple as turning on the gas. However, if regular maintenance hasn’t been performed, you could have a much bigger underlying issue. Not changing the oil in 20 some hours can do a good deal of damage to the engine. If you just haven’t ridden the bike for a few months and it’s just been sitting in the garage since you last rode it, you can often find and solve the problem in less than an hour.

In order an engine to run, it needs air, fuel, and spark. If your dirt bike is not getting just one of these, you can kick it over all day long and it won’t start. In order to save some possible time, we’ll take a quick look at each of these areas to see if we can spot something simple. That way we won’t spend an hour trying to fix one thing when the problem could be something completely different.

Oxygen

Air comes first, so pop the side cover and/or seat off and take a look at the air filter. This may be a dumb question, but is there a complete air filter there? It’s easy to stuff a rag in there while working on the bike and forget about it when you go to put everything back together. All I can say is, stranger things have happened, and it’s always safe to check first, especially since it only takes a minute. If the air filter is there, how dirty is it? If it’s caked with sand and mud, that alone could be preventing your no-start problem. Clean the filter and try starting it again.

A less-common, yet possible cause, could be an air-leak in the system. Check the intake boot for cracks, as well as any bolts or gaskets in between the airbox, carburetor, and engine. On a 2-stroke engine, the reed valve has pedals that wear out over time. They can last hundreds of hours if the bike isn’t ridden hard, but if the edges are chipped off, it could let unwanted air through and not allow the bike to start. This takes longer to remove and inspect, but it’s just one of the many things that can cause a no-start dilemma.

This filter looks a little dirty...
This filter looks a little dirty…

Fuel

The engine requires air and fuel in order for combustion to occur, so the next step is make sure the engine is getting gas/premix. First place to check is the gas tank. Is the tank clean with fresh gas? Gas or premix that has sat for a number of weeks will degrade and start to gum up. If the gas smells like old paint, dump it out before doing anything and clean the tank out. Fuel must go through the petcock to get to the carburetor, so if the tank is empty, now is a good time to take a peek at the seal and filter on it. If they are damaged, leak, or clogged, replace with new parts/assembly. If the gas line is cracked or plugged, replace it as well.

Next up is the carburetor, which is the root cause of many ‘no-start’ situations. Especially on smaller dirt bikes with smaller carbs, jets and passages can gum up in a matter of weeks because of old gas sitting in it. Even if you can see through the pilot jet, there may be just enough crud stuck on it to not allow a sufficient amount of gas through to ignite the engine. Carb cleaner and compressed air are your friends if the carburetor isn’t too filthy. You can often times just loosen up the carb clamps and rotate it to spray out the jets while still on the bike. This can be done in a matter of minutes by removing the float bowl on the bottom of the carburetor.

If that doesn’t work, you may need to take the carburetor completely off and dis-assemble it for a more thorough cleaning. There’s a couple more quick ways to confirm that the carb may be dirty. You can pour a little bit gas in the spark plug hole and kick it over. If it starts or fires for a second or two then you know it’s not getting gas from the dirty carb. You can also try and push start your dirt bike. If neither of those work, it may not be a fuel problem after all, but lets move on to one more quick check before taking the time to clean the carburetor again.

Spark

My dirt bike may be getting air and fuel, but if there’s no spark, it won’t even want to start. A quick way to check if it has spark is by pulling the spark plug off, putting the cap back on, and resting it on the engine while slowly kicking the engine over. You may need to turn off the garage lights to see it, as it will be a small, blueish spark of electricity on the end of the spark plug. If you don’t see anything, be prepared to do spend a good amount of time swapping out parts if you don’t want to replace everything in the electrical system.

If you know someone with the same bike, ask if you could temporarily rob some electrical parts off of theirs. It could be as simple as a faulty kill switch, or a bad ground in the system. However, you may have to swap out the CDI box or even the stator to find the root problem. Once you find the part causing the problem, order a new one and give your generous friend back his/her parts, as well as taking them out to lunch if they lent you a hand in your project because they could have saved you a lot of money by not ordering the wrong parts.

If you still can’t figure out why your dirt bike won’t start, there’s a good chance that it needs a rebuild if it has a lot of hours on it. Low compression is common on motocross bikes that have been ridden for years. If you check the engine compression when the engine is new, you will be able to tell when it needs to be rebuilt when the compression goes more than 25% below what it started at.

If you have any questions, post a comment below… Have fun, ride safe, and keep those dirt scooters maintained!

-Tom Stark

How To Remove and Replace Wheel Bearings On A Dirt Bike

Wheel bearings inevitably fail over time, and that time is much less if you often ride your dirt bike through water. Water and mud will eventually seep inside if you leave it wet, causing the bearings to rust and end up seizing. An easy way to tell if your dirt bike wheel bearings are shot is by moving the wheels side to side. If the wheel moves at all then the bearings need to be replaced. Some tools you will need to replace wheel bearings include:

  • Wrenches to remove wheel
  • Screwdriver
  • Punch
  • Bearing retainer tool/pliers
  • Hammer
  • Bearing installer/socket

Before taking any parts off your bike, give it a bath so that it’s easier to work on. Keeping your dirt bike clean makes working on it much easier, keeps you cleaner, and you will be able to tell much sooner if there’s a leak or other problem with your bike. Once your bike is spotless, set it on a stand and remove the wheel that you are replacing the wheel bearings on. Now put the wheel on a wheel stand, a wooden box, or even saw horses to make it easier to work on without damaging the rotor or sprocket.

Wheel Bearing Retainer Removing Tool
Wheel Bearing Retainer Removing Tool

Remove the seals by prying them off with a screwdriver so you can get at the bearings. One side will have a retainer clip or nut, such as the one on Honda motocross bikes, which you’ll want to buy the special tool for. They are pretty cheap for a specialty tool, but make sure you get the right size because they changed over the years. You can try tapping it out with a small punch if you’re careful, but I wanted to re-use the retainer, and for under 20 bucks, it’ll pay for itself even if I only use it a couple times. Tools like this will save you time and the hassle, especially if you need it again sometime down the road.

Once you remove the retainer, flip the wheel over to remove that bearing (If you bought a fancy bearing remover tool, just use that, otherwise for the rest of us that are cheap, continue reading these instructions). Before you go to punch it out from the other side, you’ll have to take the punch and push the wheel spacer that is in between the bearings over so you can hit the bearing with the punch. Now just hammer on the punch to knock the bearing out of the wheel. Punch the bearing in a circular rotation so that the bearing comes out straight and doesn’t gouge the bore of the wheel. The wheel spacer will come out once that first wheel bearing is out, so set that aside until you need to re-install it.

Now you can flip it back over and knock out the other bearing(s). Just make sure you punch them out as straight as possible. Before you install the new bearings, I recommend putting them in the freezer. Metal slightly shrinks at cooler temps, so this will help make the installation a little easier. Clean the area and surfaces of the wheel on both sides where the bearings go in and set your wheel back on the stand/wood blocks.

Some people say to heat up the hub where the bearings go to make it easier to install them, although others will say that it weakens the metal. I haven’t seen any issues caused by heating it, but it’s up to you whether you want to use heat or not. I didn’t use any on my recent rear wheel from a CR125, but it took a little more force to press the bearings in.

Take the wheel bearing and set it on the journal where you will press it in. You can start out with a piece of wood or flat piece of metal and hammer it in until its flush. Make sure you know that it is going down straight, otherwise it can damage the surface. Next, you’ll have to use a round piece of metal or a socket that is almost the same size as the bearing. You want to be hitting on the outer race (outside circumference) of the bearing and NOT the inner race. If you press or hammer on the inner race you will destroy the bearing. Keep hitting the bearing down while making sure it’s straight. You will hear or feel when it bottoms out in the bore, and that’s when you stop. Now you can put the clip or retainer ring/nut back on, along with the seal.

Removing Seal and Bearing
Removing The Seal and Bearing

Flip the wheel over to do the other side, but before you put the other bearing(s) in, REMEMBER TO INSTALL THE WHEEL SPACER. This is just the sleeve that you took out that goes in between the bearings, and it can be easy to forget until after you press all of the bearings in, resulting in hair-pulling frustration. Now you just repeat installation on this side, whether you have one or two bearings left. If you’re doing it all by hand, just be patient and get them in straight. It may take some time, but the bearings will go in (assuming you bought the correct part).

Now you can install the other seal to complete the wheel bearing installation. When you go to put the wheel spacers on, put some waterproof grease on them to help protect the seals and bearings. If they are worn with grooves then they should be replaced, otherwise water will find it’s way to the bearings much easier.

That’s it, just put your wheel back on the same way you removed it and remember to properly torque the bolts. If you have any questions, don’t hesitate to post a comment below…

Good luck, and ride safe!

-Tom Stark

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

6 Essentials For Riding Dirt Bike Alone

Finding riding buddies at any given time can be difficult at times. If it’s a beautiful Sunday afternoon and everyone is busy, but you have a perfectly good dirt bike sitting in the garage that is begging to be ridden, what’s going to stop you? Some people will never ride without someone else with them due to safety risks. While I completely understand that, some people have schedules that make it very difficult to find riding partners, and that shouldn’t make you get rid of your dirt bike.

So, if you really want to ride your dirt bike like I do but can’t find friends to ride with, it’s time to get yourself and your bike ready for some  solo adventures. Not only are there things you should bring with you in case of emergency, there’s some general guidelines that you should follow when riding alone so you reduce the chances of an accident.

Phone

Whether you’re out riding in your backyard, or 10 miles out in a forest, it’s a good idea to bring a cell phone. If you or your bike can’t make it back safely, you need to be able to contact someone for help. This alone can save you from most disasters.

Wallet/Cash

Having some ID and cash on hand can also get you out of a jam. In a worst case scenario, someone may need to know who you are and who to contact. A concussion may knock you out and cause some short-term memory loss. Also, if something breaks, you run out of gas, or your dirt bike needs a tow, having some money with you will save a lot of time, and may allow you to get help from the right person. You can put your wallet and phone in zip-loc bags so they stay dry.

Hand Tools, Not Tool Hands

Riding Alone In The Woods
Riding Alone In The Woods

Have you ever tried fixing or replacing parts on your dirt bike without any tools? It sucks, doesn’t it… This is why it’s a good idea to bring a small tool pack along on your solo rides. Adding more weight to my ride is not something I’m fond of, but in this case it can possibly save me hours of frustration. If you already ride with a small backpack, just add some of the most used tools for your bike, such as a few wrenches, a pair of screwdrivers, pliers, duct tape, zip ties, a spark plug, and anything else you might use on a regular basis.

You Might Get Hungry/Thirsty

Always bring water. You don’t always know how long you will be out for, and dehydration can be very dangerous. Not drinking enough before and during your riding session will drain your energy, and it will cause you to lose concentration. A camelbak is the most convenient way to carry water since you can mount a hose to your helmet to drink while riding. You can also store some small snacks or extra tools in the available pockets. Having a couple energy/granola bars with your water can give you just enough juice to safely get you back in home case of emergency.

Don’t Be Dumb

It’s just something I have to say because it seems like every time I get on a dirt bike I feel like conquering the world. Unfortunately, this is not the best mindset when flying solo on a dirt bike. While dirt biking is inherently risk-taking, if you’re pushing yourself as fast as you can go, an accident will happen sooner rather than later. One little divot or tree that you oversee or miscalculate and you’re on the ground. Going fast is fun, and it’s so easy to get the adrenaline pumping, but if you come up to a very challenging and/or dangerous obstacle, I encourage you to take an extra minute to decide if it’s worth taking the risk. You can stay get faster by riding in your comfort zone; it’s called riding smarter. A few little bobbles or near-misses are okay every once in a while; that means you’re running at a good pace. But if you’re coming close to hitting things or wiping out every couple minutes, you need to slow down.

Tell Someone

Last, but not least, if you’re going to ride alone, ALWAYS tell someone where you’re going and about how long you plan on riding for. A family member, a riding friend that couldn’t make it in time, or even a good neighbor if you happen to have one. Even if you’re an experienced rider, all it takes is one little accident to produce a life-threatening situation, and being stuck out in the middle of nowhere without anyone knowing where you are is one of the worst case scenarios.

This article is not to scare you from riding alone (although I believe it’s always safer to ride with someone), but merely to prepare you and to help reduce the number of dangerous situations. So please, plan ahead, ride safe, and have fun!

-Tom Stark

Bought New Motocross Boots & Can’t Shift – Break-In

Buying new motocross boots is both a great feeling and a tough one (pun intended) as well. Riding with fresh gear can be like riding a new bike because everything is tight and still altogether. However, when you buy new boots, they are usually hard as a rock and suck to ride in without breaking them in first. That is, unless, you spend several hundreds bills on a pair of MX boots that don’t require break-in.

If you’ve never put your feet in a new pair of boots, just imagine putting your feet in ski or snowboarding boots; stiff and weird to walk in at first. If you can’t bend your ankle up and down then you will have a very hard time shifting, and using the rear brake will have much less feel because you have to move your whole foot.

So, how do you break them in so they’re actually usable for a race or long day in the wilderness? The easiest, although probably the longest way is just by riding with them until the leather of the boot is broken in. Before I go any further, you should know that for dirt bike riding boots work properly and help protect your feet from injury they have to be stiff. If you happen to fall off your bike and land on your feet, and you rarely land perfectly flat, you need the boots to hold together and not flex because your feet are going to do the same.

It can take several hours of riding before your new boots are feeling comfortable, so I wouldn’t do any important rides or racing with them until they are.

If you want to break them in with little to no riding, you can work your riding boots in off of the bike. It’s as simple as bending the boots back and forth at the ankle (where it would normally bend while riding. Just grab the top and bottom of the boot with your hands and flex the shin towards the toes, and then back the opposite direction. Keep doing this for a few minutes until you feel the leather start to loosen up.

New Motocross Boots
New Motocross Boots

Once you’ve worked the boots in with your hands, put them on your feet and buckle it up. Don’t need them too tight as you won’t be riding quite yet. You’re basically doing the same thing as you did with your hands. Just crouch down so your knees are bent and rock your ankles back and forth so the boots stretch out.

After doing this for a few minutes, the your new boots should be flexed enough to be able to ride with them. Go ahead and gear up and hop on your dirt bike for a ride. This simple process will help break your fresh boots in with minimal riding. A good 30 minutes of riding with shifting and braking involved and you are ready to race again with better support!

There’s many other ways to break in your new dirt bike boots, such as heating them in the oven, walking around in them all day, as well as soaking them in water and walking around in them until they loosen up. Any way you do it, there’s going to be some break-in process before you are able to ‘feel’ the shift lever and brake pedal while riding.

If it’s hard to shift at first, try sticking the toe of your boot under the shift lever and lift your entire boot up. It’s a good technique to get used to in case you are standing and need to shift.

Ride safe, and go moto!

-Tom Stark