Top 5 Mods To Do To Your Motocross Dirt Bike

Racers are always looking for ways to make their dirt bike go faster. I’ll admit, it awesome to have a bike that absolutely rips…. I hate to break it to you, but if you can’t handle the bike on the track, there’s not much use to having the fastest dirt bike in the world, unless of course you’re straight line drag racing against your pansy friends with quads.

A pretty much stock bike that is properly set up for your weight, height, riding style, experience, and riding terrain will be far better than one that’s cranking out 50% more horsepower than everyone else (It will also be more reliable!).

1. Suspenders

Suspension Compressed

Whether you’re doing Motocross racing, hare-scrambles, enduros, or flat-track, if you’re suspension isn’t set-up right it’s not going to perform nearly as well. You won’t be as fast and will get worn out quicker because you’re either getting thrown around from rock-hard suspension, or you’ll be bottoming out and bouncing everywhere from it being too soft.

It may cost quite a bit of your money to get your dirt bike re-valved and set-up for your riding style, especially if you have to get different springs for your weight. But, the reward is more than worth it… Your bike will ride so much smoother over obstacles, and you won’t get so beat up from the abuse, allowing you to ride harder for longer.

2. Jetting

If your bike isn’t jetted correctly, it’s not going to run as well as it should, and could possibly lead to a blown engine. I realize that many of the new four-strokes are going to fuel-injected, but many people think that they don’t have to do anything if they make any modifications to the engine or exhaust. Some bikes come rich from the factory, so if you put an aftermarket pipe on it, the jetting may be pretty close to spot on. But if it was already jetted to spec, then modifications will cause the bike to run lean. The result will probably make the bike slower, and you will be slowly burning down your engine because it’s not getting enough fuel.

Rich Jetting Causes Spooge

Too rich, though, and you will be wondering why you’re eating through spark plugs. Your dirt bike will cough, sputter, and act sluggish. So now you know that too lean of jetting is not healthy for the bike, and too rich is slower and cause problems. Some people may say that too rich is fine because it’s safer for your engine, but it’s really not because you will foul more plugs, and get more carbon build-up from the gas that’s not being burned. A finely-tuned, stock motocross bike will run much better and be more reliable than a highly modified bike that isn’t.

3. Fresh Top-End

Aftermarket pipe, cams, porting, intake modifications, or even re-jetting aren’t going to help if your bike’s top-end is worn out. On a two-stroke motocross bike, this usually means that piston and ring(s), but on a four-stroke it could also have worn out or out of spec valves, timing chain, and tensioner. It all depends on what kind of riding you do and how hard you ride the bike, but a routine top-end rebuild/inspection is every 15-20 hours. A two-stroke should have a new ring installed every time you check it if you’re motocross racing. A piston can last anywhere from 15-50 hours depending on how it’s ridden.

Four-strokes have many more moving engine parts, so routine check-ups are crucial if you want the bike to last. Valves and timing chain should be checked every 15-20 hours because they can go out of spec in a matter of hours on certain bikes. A piston should last 20-40 hours of racing, but again, it depends on the rider and what kind of riding it is.

Before you do anything else, even jetting your bike, if your top-end hasn’t been checked or rebuilt in more than 20 hours, get on it! A fresh top-end is preventative maintenance, and it can bring back a couple ponies that you need to pass a rider.

4. Knock Some Teeth Out

Most stock motocross bikes come with a transmission and sprockets that are already geared well for racing. But, what if you get on a tight supercross-style track where you need to get out of corners faster to clear the next jump? That’s when it’s time to start messing with your sprockets!

Your goal for gearing is to able to rev the bike out in 4th, 5th, or 6th gear, depending on the track size. This means that if you’re in low-mid of 5th gear on the fastest part of a track, then you should re-gear it so that it’s in the meat of the power in either 4th or 5th gear. If it’s geared too tall then you’ll have to do more clutch work, and acceleration won’t be as good as it could be. Too low of gearing and you will be shifting too often.

Some people are confused when it comes to gearing, so let me explain what will happen when you change a sprocket. If you go down a tooth on the front sprocket (13 to 12), then the bike will accelerate quicker, but you’ll have to shift more and it won’t have as high of a top speed. The opposite will happen when you go a tooth larger on the front/counter-shaft sprocket (13 to 14). For the rear, if you go a tooth smaller (50 to 49), then the bike will have a higher top speed, and you won’t have to shift as often, but acceleration will be slower, and keeping it in the meat of the power will be more difficult. Vice-versa if you add a tooth to the rear. Also, don’t forget to adjust your chain when you change sprockets.

5. Smoke ‘Em With A Pipe

Ok, I know you’re probably thinking, “Why aren’t any performance parts on this list?!” Well, it’s kinda’ like what I previously said… A stock bike that’s finely-tuned and properly set up is faster than a bike with thousands of “hop-up” mods to make it go faster. You must realize that 90+% of racing is the rider and NOT the bike.

Aftermarket Exhaust

Anyway, the reason exhaust is even number five on this list is because they can change the power-curve to suit the rider and riding style. Exhaust systems are actually pretty good these days, so most bikes won’t gain much power from an aftermarket exhaust (yes, even after re-jetting it!). They usually move the power around more than anything (especially on two-strokes).

A pipe that offers more low-end to mid-range power is better for beginning riders and woods riding. For outdoor motocross tracks and riders that like to wring their bikes out, a pipe for top-end power is best suited. When looking for the right exhaust pipe, keep in mind that if you add power to one end of the RPM range, it will probably lose some on the other end.

Remember that these are my top 5 mods for a motocross bike. But if you ask any good rider that knows what they’re talking about, I could guarantee that their top 5 mods are most if not all of these as well. Good luck, and have fun racing!

After all that hard earned money spent, Dirt Bike Insurance is something to consider in case something happens.

-Tom Stark

YZ125 Big Bore 144cc Kit – Is It Worth It?

Are you looking for that little extra power to get over a certain jump? Or is it because you want to prove to your four-stroke friends that two-stroke dirt bikes still have what it takes? Either way, a big bore kit can help you do that.

’01 YZ144

YZ125’s are the most common 125’s in U.S., and for a good reason. Yamaha is the only Japanese manufacturer that imports two-strokes to America. They are fast, light, reliable, and fun. But, for some of us that just want a little more out of a small-bore two-stroke, an upgrade in displacement is probably on top of the modifications list.

Just Because It’s 144cc, Doesn’t Mean It’s A 144…

You can get a bored out cylinder that’s 144cc’s, but to actually perform like a 144 it will need some tuning. This is why you will hear positive and negative comments from people who modify their 125 to a 144. Most of the time, it’s the people who buy just a cylinder kit that give bad feedback. This is because the cylinder, carburetor, and exhaust are not properly tuned for the extra “cc’s”. When I say a cylinder kit, I’m talking about one you can buy from a company like Athena and just bolt it on.

You Can’t Go Faster Without More Gas

Too many people think they can make their dirt bike faster by bolting on parts and not do anything else. Motocross bikes are high-tech racing machines, so it’s critical that they are finely tuned. If you don’t tune a bike after putting on a “hop-up” part, it’s probably going to run worse, and possibly break shortly down the road. More power requires more gas, so if the carb isn’t feeding enough fuel to the cylinder, it’s not going to run like it should. Although it may need more gas to make more power, some mods require different things as far as jetting goes. A bigger engine is going to suck in more air/gas, thus requiring leaner jetting to make it burn properly. You will have to go down on the main jet at the minimum. A change in pilot jet and clip position on the needle may also be required for optimum performance.

Bigger Engine Needs Bigger Pipe

Take a look at the size and shape differences from a 125 to 250 two-stroke pipe if you haven’t before. Bigger engines need bigger pipes to take advantage of the higher displacement. Yes, that means if you’re using a stock pipe on a 144, then you probably aren’t making the most out of the engine. Some companies make special pipes for big-bores, but may cost a little more (still cheaper than four-stroke exhaust by a long shot). If you want to stick with FMF or Pro Circuit, do some research on which pipe works well for your dirt bike, because not every pipe and bike combination will give you the same result.

Build The Ultimate 250F Killer

KX144 Eric Gorr Big-Bore

Now if you get your 125 two-stroke bored and built by a reputable bike builder, it can be out of this world. In addition to boring and plating the cylinder, most builders will port the intake and exhaust ports to your liking (either low to mid-range or mid to top-end power for most builders), change the port timing, possibly do some case mods if you send your entire engine in, and cylinder head mods if you want higher compression (will require race gas). In result, this will make a screaming-fast small-bore two-stroke that will outrun 250F’s and keep up with 450’s with an experienced rider. Oh yeah, did I mention most shops can do this for relatively cheap too!? That’s right, who needs a high-buck four-stroke when you can eat them up with a finely-tuned 125/144…

Athena Didn’t Know What They Were Doing…

While I admit that I’ve never owned a 125 with an Athena 144cc kit, I’ve done plenty of research to find up what’s up. In fact, I didn’t have to go very far to find out if it’s worth it or not. Review after review showed that the Athena top-end kit did not improve the stock YZ125 by much. They basically took the stock cylinder, increased the power-valve size and ports, and called it good…… You can see a slight increase on the dyno, but to really feel the effect of the extra cubic-centimeters you have to port it like you would a stock cylinder. The port sizes, shapes, and durations will not be the same as a 125cc if tuned correctly. This is when the reputable two-stroke engine builder comes in. There are builders that really know how to open a 144 up to its potential, so don’t settle for less. Here’s a great example of a YZ144 Athena Kit Test done by Motocross Action Magazine. They do an in-depth review of it, and in the end their YZ barely makes an extra two ponies, and that’s with a GYTR pipe and silencer made for the 144!! If it’s properly tuned, I honestly think you should be able to crank out 5-7hp more than a stock 125.

Click Here To Buy My Athena Big Bore Kit

-Tom Stark

How Much Does It Cost To Race Motocross

I’m really glad you’re considering participating in this extravagant and addicting extreme sport, but there are some downsides to doing it as well, unfortunately. Cost is the biggest reason why so many people aren’t able to race motocross, whether it be the cost of bikes and maintaining them, or having to pay for entry fees, gas for bikes, gas for vehicles, food, etc.

Dirt Bike

Your dirt bike is probably going to be the most expensive part of motocross racing. You can find a good motocross bike for $1500 or less, as I show you how in that article. But if you want to go the four-stroke route, you will probably have to pay more for the bike, and it will cost more in the long run to maintain and repair.

Bike Maintenance/Repairs

Depending on the route you go, the amount you can spend on keeping a bike running can vary greatly. Two-strokes generally require a little more maintenance, but when it comes time to rebuild the engine, they’re usually much less than a four-stroke. Now when I say maintenance, I’m talking about your regular oil changes, air filters, tires, chain, sprockets, and fluids.

If you’re going the four-stroke way (not that it’s bad, but it will more than likely cost more), maintenance should consist of changing your oil every 2-3 rides, and replacing the oil filter every other time you change the oil. Air filter should be cleaned/replaced every 1-3 rides, depending on riding conditions. This simple and cheap maintenance will keep your four-stroke running much longer, which is why they appear to be cheaper to race. You may end up finding out that this is not always true, unfortunately, when the engine grenades on you. It’s important to know When & Why to replace your valves and timing chain on a four-stroke, because these parts can fail in the blink of an eye. Many people fail to realize that these parts should be considered maintenance on a four-stroke motocross bike, so keep that in mind.

Rebuilding CR80 Top-End

On the flip-side, you don’t have to deal with a valve-train on a two-stroke, which is why they are cheaper to keep running in the long run. Maintenance is similar to a four-stroke, other than the oil filter, but you may go through top-ends quicker if you’re constantly wringing it out. This is another reason why many people think that two-strokes are just as expensive, if not more. But they are only looking at the intervals of engine rebuilds, when the real difference is how much they cost to rebuild. A two-stroke can last 15-20 hours, even with a fast A-rider on it. A four-stroke may or may not last longer than that before you start replacing engine parts.

Gas Hog

Next you have to consider gas, both for your bike and your mode of transportation. This all depends on what bike you’re running, what gas, how many classes you’re racing, and what vehicle. A two-stroke uses pre-mix, so oil will cost a couple bucks extra, but some four-strokes require race-gas (i.e. high compression), so they may even out. If you’re running two classes, that’s twice as much gas you’re going through (duh!), so consider that factor. Trucks and SUV’s can be gas hogs, so if you want to save money on that, either get a small truck (S10/Ranger), or you can get a Motorcycle Carrier to insert into the hitch of your van or truck instead of pulling a trailer.

Race Fees

Next thing to consider is the cost of entry fees and memberships. An average cost of one class of racing is $30 around here, and usually a little cheaper if you do more than one class. Yearly memberships (District and AMA) add another $40-50 each. So the cost of entry fees comes down to how often you’re going to race and how many classes.


Don’t forget about food! You have to eat and drink, whether you pack for a picnic at the track or buy food there. Camping will also cost extra if you spend the weekend at the track, which many riders do if they have a camper or RV. Also, you will sometime or another have that unexpected problem; a blown tire, or crash on your bike that breaks several parts.

If you want to prevent a mid-life crisis, Dirt bike & health Insurance can save your butt in the case of a serious injury or stolen bike.

You Can't Get Enough Motocross

There are probably a couple more things you could have to add to the cost of motocross racing, but do you see now why so many people cannot afford it, especially when they’re not prepared? I really don’t want to scare people away from this terrific sport, I just want YOU to be well informed of how much you can expect to pay if you want to start and continue racing for years to come. After you figure out that you are able to do it or have enough money, check out my tips for first-time motocross racers so you won’t be left in the dirt. Also, don’t forget to get footage of your first race with an HD Helmet Cam!

That should cover just about everything, so here’s an overview of what it will cost (based on if you race about every other weekend:

Dirt Bike: $2000 (guesstimated cost of a good running bike)

Maintenance (Oil, filter, lube, etc.): $50 every couple races

Engine Rebuilds (Varies greatly): Two-stroke top-end $150 every 20 hours, $300-800+ every 25-40 hours

Gas: Depends on vehicle, $10-30 depending on how much racing

Memberships: ~$90 for District and AMA

Race Fees: $30 Each race (more if you do multiple classes)

Misc (also varies greatly): This is one category I cannot really determine for you. It all depends on how much/where you eat, what you buy, what breaks, and all that jazz.

You may not, and probably won’t go exactly by this last, because there are many factors in motocross that can cost more or less. Using guide as a reference will give you a good idea of how much this sport can really cost, and why it is slowly dying in some areas. Keep it alive if you can, and have fun riding!

-Tom Stark