Yz 125??

[93YZproject]

Does the Yamaha YZ models(125cc) make for a good trail riding bike for a novice moving up from a xr100r cc Honda trail bike? Ive heard that these are racing machines. Will forest and trail riding be ok for this machine??

 

[XRpredator]

moving up from an XR100? You'll have a hard time for a while. A flywheel weight will mellow it some, but it's like comparing apples to butler monkeys.

 

[93YZproject]

why would it be hard? i know its a lot more than an xr but it rides just like another bike doesn't it?

 

[rmc_olderthandirt]

I would not expect you to have any problems. If you were a first time beginner I would hesitate a little bit but I would expect you to be tearing it up and doing just fine.

The only issue you might have is if you end up riding really slow due to another rider. If they run too cold for too long you can end up fouling a plug.


Rod

 

[codyj]

due to the overall power of the yz 125 you'll be in for the thrill of that power band kicking in, you'll do fine just takes a while to get used to it

 

[93YZproject]

Thanks for the info. im curious though as to how a power band works. I have a yz 80 and i can feel the power band on that but i dont know how it works. can anyon shed some light on this?

 

[codyj]

Thanks for the info. im curious though as to how a power band works. I have a yz 80 and i can feel the power band on that but i dont know how it works. can anyon shed some light on this?

power band which refers to the range of operating speeds under which the engine is able to operate efficiently. A typical gasoline automotive engine is capable of operating at a speed of between around 750 and 6000 RPM, but the engine's power band would be more limited. The engine would typically not generate maximum torque until higher operating speeds of perhaps 2500 RPM, after such, the torque drops off. The peak power (horsepower) might be closer to 5000 RPM. Such an engine would be said to have a "power band" of 2500-5000 RPM (another example would be from torque peak to redline: 2500-6000 RPM).

This can be applied to any engine and establishes a reliable quantification of the above notion "the engine is able to operate efficiently".

 

[XRpredator]

Thanks for the info. im curious though as to how a power band works. I have a yz 80 and i can feel the power band on that but i dont know how it works. can anyon shed some light on this?

now you said you were moving up from an XR100. If you are moving up from a YZ80 to the YZ125, you'll adapt just fine. The 125 might even be easier to ride since the power valve will broaden the powerband more so than that 80.

 

[93YZproject]

now you said you were moving up from an XR100. If you are moving up from a YZ80 to the YZ125, you'll adapt just fine. The 125 might even be easier to ride since the power valve will broaden the powerband more so than that 80.

i am moving up from an xr100. The 80 is a little to small for me and it doesn't have the power that the 100 does but i have ridden the 80. sorry if i confused anyone. and thanks again for the information.

 

[rmc_olderthandirt]

"Power band" is usually a term applied to two stroke engines.

A four stroke engine will develop a fairly uniform torque from a low RPM until the restrictions of the intake/exhaust limit the amount of fuel that can enter the engine. If the torque remained constant the horsepower generated would be a linear function of the RPM. Certainly more power at higher RPM, but the accelerate you feel will be constant because the torque is constant.

A two stroke is a different animal. While the four stroke uses two of the four "cycles" to force exhaust out and draw air/fuel in the two stroke has to accomplish the same task in much less time. To aid in the flow of exhaust the pipe has a specific shape to it.

Look at the exhaust on a four stroke: A pretty simple pipe connecting the exhaust port to the muffler.

On a two stroke, the "pipe" starts small and then gradually increases in size, to a point. Then it skinnys down again, ending in an even narrower outlet than the input. The pipe has a tuned "resonance", and just like a musical insturment it has a specific frequency that it operates at.

When you are "on the pipe" the exhaust gases start flowing into the pipe under fairly high pressure. The exhaust gases have momentum, and once they are moving they want to keep moving. As they move deeper into the pipe the expansion causes the gases to cool, thus reducing the pressure and making it easier for the exhaust to continue to flow.

Towards the end of the cycle the momentum in the gases along with the rapid cooling will actually create a suction back at the exhaust port of the cylinder. This helps draw the fresh air/fuel into the cylinder and will even draw some air/fuel all the way through and into the pipe.

Now the magic happens. The exhaust gases, which are moving fairly fast in the pipe, hit the restriction at the end. Air bounces. The resulting back wave pushes the gases back towards the cylinder. Remember that excess air/fuel that got sucked into the exhaust port? That gets pushed back into the cylinder, effectively "supercharging" the mixture in the cylinder, dramatically increasing the torque the engine will deliver.

Depending on the design of the pipe this effect can be VERY "peaky" or a broader, more gentle effect. You can buy pipes that provide more boost at higher RPMS or other pipes that provide the best boost at lower RPMs.

The boost from the pipe only happens at certain RPMs. If you have a very "peaky" pipe the effect can be very dramatic and come on so suddenly that it is hard to get used to.


Rod

 

[SpeedyManiac]

A YZ80 makes a lot more power and is physically bigger than an XR100R. I'm guessing you have a PW80. I think a YZ125 is a terrible choice for a rider moving from an XR100R unless you are really into riding. 125s are brutal trail bikes as they only really make power from 3/4 throttle to WFO. An XR100R is very mellow - it tops out at about 6-7 HP and makes a ton of low end power. It also has a huge flywheel for the size of the bike so it's very lugable. In comparison, a 125 makes around 30 HP at high RPM. They have extremely light flywheels so they don't lug much, if at all. You need to be very adept at slipping the clutch in order to take a 125 anywhere on the trails.

How big are you? If you're big enough, a better bike would be a 200 two-stroke as they're easier to ride.

 

[93YZproject]

No its a yz80 but its very old and it does not take me up hills as good as my xr100. I'm not sure why but thats the way it is. Anyway we did get the yz125 and it is a handful, but nothing we can't learn how to ride. Thank you for all of your advice. SpeedyManiac what did you mean about slipping the clutch?

 

[rmc_olderthandirt]

Speedymaniac must ride much more radical "trails" than I do.

What is meant by "slipping the clutch" is that when you need more power, especially when climbing a hill, you pull the clutch in part way to allow it to slip. This increases the engine RPM, gets the engine into the power band and generally produces more power. To make use of this you need to learn to "feather" the clutch so that it slips enough to keep the RPM up but grips enough to move you forward.

What I call a trail would not need such a technique. For most hills if you get on the pipe and stay on it you can climb okay. It is when you slow down going up the hill, or come to some obstacle that you need to power over that slipping the clutch becomes essential.

Don't over do it or you will ruin your clutch. The slipping heats things up real quick.

Rod