How To Swap TTR125 Carb to VM24 – Video Tip

Having starting or running problems with your TTR125? There’s a good chance that the stock carburetor is your problem. Instead of spending hours trying to fiddle with it, a carb swap can save you a lot of headaches and make your bike start easier and run much cleaner. Here’s a step-by-step video tutorial on how to convert to the Mikuni VM24 carburetor. If you’re unsure about this conversion or have questions on why you should do it, read all the details on swapping out the stock carb HERE.

KX250F & RMZ250 2004

2004 Kawasaki & Suzuki 250F

2004 RMZ250

If you’re looking at getting an older 250f, and possibly a Kawasaki or Suzuki, then you should probably consider some of this info. When these companies made their 250f, it was more like a Kawazuki 250f, because Kawasaki and Suzuki had partnered up. So most of the parts on these bikes are interchangeable. This was their first year making the 250f, so just by that you should be a little worried.

2004 KX250F

As some might expect, these bikes were not the greatest reliability-wise in 2004. Although they were fast bikes, they had an overheating problem caused by a bad/weak water-pump. Another defect these bikes had was in the valve-train that caused the valves to burn-up more quickly. These problems can get bad and scared me away from buying one of these bikes. This is not to say that these bikes do not perform. They have plenty of power, and if you really want to get one then I suggest you get a newer style complete cylinder head and get and aftermarket water-pump and impeller to fix the overheating problem. If you do that then the bike should be fine, but by the time you spend all that money on parts you could have bought a newer bike more than likely. Good luck, and remember that no matter what you ride, have fun and stay safe! Thanks

-Tom Stark

 

How I Built A YZ250F With A Box of Scraps

What do you get with a bin full of dirt bike parts and an eager mechanic looking for excitement and satisfaction? A great project rebuild! If you are a dirt bike grease monkey like me who not only likes riding their bikes but sometimes working on them too then this is for you. I enjoy project rebuilds and love the oh-so greatly anticipated finished product even more. Ever since I got into dirt biking I have gained more knowledge about how they work and how they are put together. So after doing many rebuilds myself I thought that I would share the experience with you fellow riders.

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I bought this 2003 Yamaha YZ250F in pieces as a project bike thinking that I would have some fun and get some more experience putting another bike together over the next month after I bought it. It came needing a complete new top-end at the least. I managed to get one and put the engine together in a reasonable amount of time. I then slapped the engine in the frame and started the process of puzzling the rest of the bike back together; this is where the fun started. It only took a few short minutes of bolting parts on to find that there was stuff missing. The more I put together the more parts I found that were missing or broken, and they were not all at the same time. So one-by-one I had to buy parts that I needed to piece this thing back to its somewhat original form. These parts consisted of, including engine parts, clutch plates, radiator shrouds, timing chain, timing chain slider, a different piston, head pipe, a couple crank bearings, engine/frame mounts, air filter, cylinder head breather hose, chain, gas tank, clutch perch assembly, a shift lever, and maybe a couple other miscellaneous things. Figuring out that we had to find and buy these parts got a little frustrating because we were told that the bike was complete and that it just needed a new top end.

Well, after weeks of picking at my wallet this bike has finally been put together and is running. It just needs a couple things put on to be ride able. So once I get those together I’ll take it out for a spin. The process was long and somewhat miserable, but I think I learned a lesson and gained more experience and knowledge about these modern four strokes that basically took over the world. In the spring, if not sooner, I will be putting on some new bling to make this baby look new, but as of right now it’s a clean bike that runs. Thanks for checking out this rebuild process, and make sure to check back in the near future for another bike rebuild! (If you liked this article make sure to check out my other rebuild, “I Rebuilt My YZ125 In A Closet!?

-Tom Stark

P.S. I might update this article with some pictures and/or video once I get this bike looking good. Questions and comments are welcome.

When I got the bike (as you can see, I had my work cut out for me):

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Pic of the damaged cylinder head:

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After I cleaned it up and the engine was together in the bike:

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Put the wheel and handlebars on:

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The bike put together (added sub frame, carb, electronics, old plastics, seat, exhaust, cables, etc.):

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The finished product…

 

Why Does My Dirt Bike Keep Fouling Spark Plugs?

Sick of having to replace the spark plug on your dirt bike almost every ride? Chances are, it’s a fairly easy fix. But there can be several variables to the equation. Incorrect jetting is the number one cause of plug fouling, but we’ll get a little deeper into what the most common causes could be and how you can fix them before spending a ton of cash on spark plugs.

No Air = No Combustion

Dirty Air Filter

First thing to do if your spark plug has been fouled is to check the air filter. If it’s really dirty, that makes it difficult for air to get through to the engine, causing a rich condition. Either clean it thoroughly with some Air Filter Cleaner, or buy a new filter. Before you put it back in the air-box, treat with some air filter oil or spray. BE CAREFUL, though, because adding too much oil can also clog up the filter, resulting in another fouled plug.

What Mixture Are You Smoking?

(For 2-Strokes) While the gas/oil ratio doesn’t equate to what the jetting is, you can still foul plugs, or worse, if the mixture is wrong. Depending on your bike, it’s best to look at your owner’s manual for the correct ratio. For most 2-stroke motocross bikes, a ratio is 32:1 or 40:1, gas being 32 or 40, and oil being 1. For those that don’t it, it means that for every 128 ounces (one gallon) of gas, you add 4 ounces of 2-stroke oil for a 32:1 ration, or just over 3 ounces for a 40:1 ratio.

If you have too much oil in the mixture (such as 12:1), then you will probably end up fouling the plug because it is more difficult to burn that much oil. Don’t try to cut corners with the oil though, because it’s very important for your dirt bike’s engine. 2-stokes need the oil for lubrication on the cylinder walls, so if you don’t have enough (or any for that matter) then the cylinder walls will run dry, causing it to overheat and seize the engine very quickly. So it’s very important that you put in the right mixture pre-mix to your 2-stroke gas tank.

Also, 2-strokes have reeds that air and fuel go through into the cylinder, so if they are cracked or broken the bike will not run right. This could cause the plug to foul, so before you go out and buy anything expensive, make sure the reeds are still good.

Too Rich

Turn Up The Heat!

While this usually isn’t the main problem, it could be that your spark plug isn’t burning hot enough. Having a hotter spark will ignite the fuel stronger, leaving less residual gas/oil in the cylinder that could cause the plug to foul. This isn’t the best choice, but I’d say it’s safe to go one plug hotter than stock. Spark plug manufacturers aren’t always the same, so make sure you find out how they rate them.

4-Strokes Foul Plugs Too…

Don’t be fooled into thinking that only 2-strokes foul plugs. 4-Strokes, although it is not as common, do foul plugs. Like I mentioned before, improper jetting is the main reason why dirt bikes foul spark plugs. Almost every motocross bike comes rich from the factory (especially Honda 2-Strokes when they were being made). It’s usually a pretty simple fix, but many riders are too lazy and would rather continue buying plugs instead of spending a few bucks a jets.

Can 4-Strokes Foul Plugs?

If you know for sure it’s a jetting issue that’s causing the fouling (you’ll know this by looking at the plug, which I’ll cover on how to read one in a future article), then the first thing you should do is go down a size or too on the main jet. Your goal is to get a crisp throttle response at any rpm. If you ride in the lower rpm range often, then you’ll want to go down on the pilot jet and lean out the clip position (learn the Basics of Jetting Here). By leaning out your bike, your bike will not foul plugs as easily, allowing you to ride all day long.

You Can Always Just Ride Harder

If you want to go the easy route (well not really!), just ride the bike harder. Spark plugs usually foul at low RPM’s, so if you’re wringing your bike out you shouldn’t have as much of a problem!

IF NOTHING ELSE WORKS!!!

If you’ve tried all of the above, then there’s a chance your dirt bike will need an engine rebuild. A worn out piston can cause a rich condition, which results in the plug fouling. So if the top-end hasn’t been rebuilt for a while, you’ll want to do that. Not only can this solve your plug/jetting issues, but it may prevent a major engine failure in the near future because of worn out parts.

Good luck, and keep that bike running strong!

-Tom Stark

Wikipedia: Revolutions per minute is a measure of the frequency of a rotation.

250cc Motocross Two or Four Stroke?

250cc 2-stroke vs. 250cc 4-stroke

If you’re looking to get into racing motocross at AMA sanctioned tracks and are wondering which bike to buy for the 250cc class, then pay attention. Although the four-strokes have pretty much taken over the motocross market lately, it seems that there are a lot of people trying to bring back the two-strokes, and it seems to be working. AMA made it legal so that a 250cc two-stroke can run in the same class as a 250cc four-stroke. Now, the first reaction I had when I heard of this was without doubt to pick the two-stroke. I looked into it a little bit more and came up with this….

250cc Four-Stroke

YZ250F 4-Stroke

Now most people would think that a four stroke with the same displacement as a two-stroke would not have a chance, and that is why the AMA originally allowed the four strokes to run a bigger engine in 1998. This isn’t the case, due to the fact that companies have put so much more money and effort into making the modern four-strokes extremely high-performance. Some riders that do not like the two-strokes snappy power will often stick to the four-stroke 250 just because they like their broad and easy-to-ride power-band. A 250 two-stroke may have more peak power, but when the day gets long and the track starts to get really rough, that’s when the four-stroke starts to shine. Due to the tractability in rough and slick conditions, the four-stroke will be easier to ride faster late in the day. That doesn’t mean it will be faster than a two-stroke though…

250cc Two-Stroke

Two-strokes are fun to ride because they have a bigger top-end “hit” compared to the four-stroke. If you keep the two-stroke on the pipe then it will definitely be faster than the 250F, as long as the conditions aren’t too rough. For those of you that want more, snappy power, and a lower center of gravity, then go with the two-stroke. It may not always have the traction that a four-stroke has in rough or slick track conditions, but the horsepower makes up for it.

YZ250 2-Stroke

So Which Bike??

After reading the info on each bike you would probably guess that the two-stroke is the better bike for AMA racing, and my answer for that would be, “Yes.” Clearly, it’s a faster bike if the track is in good shape, it handles better because it has a lower center of gravity and is a 2 stroke, it has a lighter front-end allowing you to skim over whoops and bumps, and it smells good. But I will say that if you are a four-stroke guy that doesn’t like the snappy-feeling power-band on the two-stroke, then you will be fine on a 250F. The 250F is by no means slow, and any good rider should be able to win on it. My choice would be to ride the 250 two-stroke though because it’s faster, and it’s a new rule that I would take advantage of. Good luck, and no matter what stroke you ride, have fun!!

-Tom Stark