Dirt Bike FAQ

There is no real way to get it quiet with out affecting your performance…You might re-pack your silencer if that has not been done..But all and all they are noise-eee..If you start pluging things up the bike wont run right…..The exhaust on 2-strokes are tuned for the motor…If you change just say the silencer from stock to a short one.. with stock pipe…You could take a 1000 rpm's off the top rev….

Just ride your bike away from hippie..ville

The four strokes refer to intake, compression, combustion and exhaust strokes that occur in a four stroke engine.
1 Intake: the fuel and air are brought into the cylindar
2 Compression: the fuel-air mixture is compressed.
3 Combustion:this mixture is ignited by the spark plug to repel the cylindar back and thus giving the energy to drive the engine.
4 The Exhaust stroke: The resulting fumes are expelled on the cylindars return.

In a two stroke engine the strokes combine these mechanisms so that on all four of these can be combined into two strokes.

You may want to check this out too: http://science.howstuffworks.com/two-stroke1.htm

Go to BBRMOTORSPORTS.COM and get a Powroll Thrust Chamber and you will get the performance of a aftermarket exhaust without spending 300 bones. Then get a rev box. It will let your motor rev past the stock limit witch will give you more hp. That is a good hp gain for under a 100 bones.

If you want to spend a little more money you can have the flywheel lightened at BBR for a hundred bucks. This will let you motor rev like a 2-stroke and make it pick up RPM's fast. If you do alot of wide open riding, this is the thing to do. "This will take away some of your bottom end."

If you still want more than get a big bore kit. If you do go with the big bore kit thin you will need to go with 26mm carb. The stock carb was not made to handle a bigger bore than stock.
P.S.- It is better to buy a complete kit than have the stock cyl. bore. Watch e-bay for these items and do not buy a china knock-off.

You just did a motor job.
-Double check the valve clearence.
-Make sure the valves aren't leaking. Bring the piston to TDC of the compression stroke (both valves closed). Remove the spark plug. With a blow gun, blow air in the plug hole and listen at the air box and exhaust pipe. Any hissing and you need a valve job.
-Double check the points and timing with a timing light.
-There might be water in the gas. Water floats in gas. If it was in the carb float bowl, when you rev the motor, the water would get sucked into the jets, clog them and drop back into the float bowl.
-Drain the float bowl into a cup and see what comes out. Anything bad, drain the tank and install an inline fuel filter.
-Clean the carb and jets with carb cleaner in a spray can.
-The float level could be to low. Remove the float bowl. Hook up an auxilery fuel supply. Turn on the fuel and lift the float by hand. -The fuel should stop when the float is level with the carb/float bowl mating surface.
-Try adjusting the needle height (on the throttle slide in the carb). Adjust the circlip up or down one notch at a time.
-If you can't get it fixed from all the answers you get here, then it's time to have a mechanic look at it.

What's the difference between a 2-stroke engine and a 4-stroke engine?
Gasoline and diesel engines are both available in either 2-stroke or 4-stroke versions

In a 4-stroke engine the sequence can be written:

Compression Stroke. The piston goes up and compresses a fuel/air mixture (in a gas engine) or just air (in a diesel).
Power Stroke. The fuel is ignited (by a spark in a gas engine, by being injected into high temperature air in a diesel.) The energy released drives the piston down. This provides the momentum necessary to keep the crankshaft turning and make the other three strokes happen.
Exhaust Stroke. The piston goes up and pushes the burned gases out the exhaust valve.
Intake Stroke. The piston goes down and draws in new air, or fuel/air mixture, ready for the next compression stroke.
In a 2-stroke engine, the last three strokes are combined into one.
Compression Stroke. The piston goes up and compresses a fuel/air mixture (in a gas engine) or just air (in a diesel.)
Power Stroke. The fuel is ignited and drives the piston down. As the piston goes down it not only turns the crankshaft but also pressurizes the fuel/air mixture in the crankcase which is about to be admitted to the piston for the next cycle. Near the bottom of the stroke, an outlet opens and the exhaust gases are released. Even nearer the bottom of the stroke, an inlet opens and new fuel/air (which was just pressurized by the piston) rushes in ready for compression.
Because a 2-stroke engine gets a power stroke twice as often as a four-stroke engine, it puts out about twice as much power (and makes twice as much noise) as a four-stroke engine of the same size.

The downside is that, because the 2-stroke engine is sloppier about how it expels exhaust and takes in fuel, doing them almost at the same time, it is more polluting. Also, the 2-stroke engine lets fuel into the crankcase, where the piston can pressurize it prior to intake. In order to keep the crankcase lubricated, you have to add expensive lubricants to the fuel, and even so, 2-stroke engines don't last very long.

So 2-stroke engines are used in chainsaws and lawnmowers, where power/weight is important, but the engine isn't used for long periods so pollution and engine life are less of a concern. The continuously used engines in cars and trucks are 4-stroke engines.

Exhaust from the dirt bikes exits and the heavier partials, unburned oil partials, fall into the dirt. The rubber tires have a reaction with the oil making them slightly blue. So the answer is the oil in the dirt.

It'll run worse because you''ll lose back pressure. And upset the neighbors, who'll petition the law to have dirt bikes banned.

Well done.

The common way to restrict the DT125R (& LC) is to unlink the powervalve on the lefthand side of the engine (as you sit on it), depending on what is there it could be a case of replacing a cable. You can turn the valve to the on position, while that gives you more top end the range suffers until you hit the powerband. The youtube videos show the position and operation.
Pre-powervalve DTs used a restrictive washer in the exhaust header.

Replacing the reeds will ALWAYS help the performance of any 2 stroke machine, espesially if you have never replaced them before.
Take off your exhaust pipe and inspect the piston and the rings. You will be able to see the piston and the rings with a flashlight, the take off the intake, where the reeds go, and inspect the piston that way as well, you may need a new top end. As far as the sucking noise goes, it may be jetting, a partially blow ring, or bad reeds. Spend the money and get it all done at once. But do not buy stock reeds from a dealership, instead ask for Boyesen racing reeds, the last longer, and are half the price….

There are a variety of good options for you. I would recommend a 4-stroke for trail riding for the wide powerband, the low end torque allows them to just keep on chugging. Though there are some perfectly capable 2-strokes out there for trails.
For trail riding, I would recommend against a moto-x or "racing" style bike. The gears are too close and the lowest ones are often too high for real technical trail stuff.
Some of the ones I am familiar with (through ownership) are the
WR-250 and the XR-250.
I moved up to the XR-250 from an XR-200 and it is a WORLD of difference. It surprised me greatly, so make sure you start carefully moving up from an 80. The engine is vastly superior, and it can do 3rd gear wheelies without popping the clutch :P. It's among the best off road machines I've ever ridden, the powerband is perfect. It also has disk brakes on both tires (unlike the 200), which you definitely want.

The racing derived bikes, like the WR (based off the YZ), is basically a racing bike with different gearing and a few trail oriented changes. Usually they keep the same high-output high-compression racing motors, which can be finicky. Some of them even recommend a rebuild after every racing season (or more frequent!), though trail riding doesn't put as much strain on it. The XR has an air cooled engine, which I've noticed can get VERY HOT in the summer when your not able to move very fast for a while. The racing derived bikes tend to be liquid cooled, but are a tad more high-strung. I've had issues with both bikes with hot starting, especially after being dropped (the XR not as bad, but sometimes it can be stubborn). If you get a bike that uses a decompress to help start (WR does, XR has one but doesn't need it), it helps if you can get one with an auto-decompress exhaust cam (greatly eases starting), or electric start (though I personally won't ride a bike that ONLY has an electric start). The WR I believe has come with a decompress standard for quite some time now (and I think electric start now too), but I had to retrofit my older model with the cam. 2-strokes do tend to start easier, I will concede that to them ;).

Things you want in a trail bike:
tons of low-end torque
disc brakes, front and back
lower, wide ratio, trail gearing
comfortable (enough) seat
probably more I'm forgetting…

almost all bike manufacturer's make a good trail bike around that displacement class. Hit up the bike forums and reviews and see what people have to say about the bikes your looking at.

best of luck on your decision and have a blast!

edit: forgot to mention, if you like the Honda CRF250, check out the CRF250X model, it is the Honda equivalent to the WR, with the different gearing, etc. from the full out racing bike.