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2003 125sx... rev limiter??


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I recently bought a 2003 125sx. Great bike, excellent condition, all stock and well maintained. It is very peppy. When I pin the throttle it doesn't die or sputter, but it seems to reach a point where it will not rev any higher, it doesn't wind out. I am used to 4 strokes, and this is my first 2 stroke bike, so I am unfamiliar. Is this normal? Does it have a rev limiter?

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If it is not running to its potential those things will change how high it revs and how much power it has or limit power if something is wrong and could be a problem.

However, from what you said there may be nothing wrong with it. To answer the other part of your question about rev limiters and in the interest of discussion:

I am not an expert on modern two strokes and there is some debate as to weather two strokes have rev limiters, but from what I have read and experienced, I don't think they do. Some small low power engines in non dirt bike applications may have rev limiters. I don't think any modern two stroke dirt bikes has a rev limiter built into the ignition with the exception of some small bikes for kids that are switchable to limit power that I have read about. I have heard and made 4 stroke dirt bikes hit the rev limiter. I have never head or made a two stroke do that, even when pinning for a second in a no load free state when trying to raise the nose in the air. I wouldn't be surprised if some of the ignition mapping promotes loss of power intentionally after some RPM but this is not a rev limiter in the sense of a four stroke rev limiter.

Two stroke dirt bikes are designed to develop power through a certain band of RPM and are apparently self limiting to some degree past that because the power flattens out to the point where they loose power and don't rev much higher even in a free state. BTW, that doesn't mean it is good for it to rev that high but generally they seem to hold up to it and just wear faster if you ring the snot out of it all the time.

I am not sure if this is where you were going and like I said I am no expert. I have only ridden a few modern two strokes so someone can tell me how I am all wrong and what bikes have rev limiters. I am curious. How about it guys?

Gary

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Here, I will argue with myself.

There is a rev limiter built into all dirt bikes. It is the throttle.

BTW, when you reach the point in a good running bike, that is jetted properly and the power valve is working like it should, where the power start to fade you have just past the point where you were supposed to shift. ­čĹŹ

Gary

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More thoughts:

Most modern motocross thumper's rev higher and carry power longer (higher) then their two stroke counterparts. We usually dwell on the low end differences but four strokes carry their power over a much larger power band. Also, that doesn't mean four strokes have more power. Obviously to compete with a two stroke they had to allow them to be larger. a 250 two stroke vs a 450 four stroke, etc. I thought you might be experiencing this difference in range and topping out earlier on the two stroke in coming from four strokes to two strokes.

In this article they are comparing a 2st 250 to a 250F even though they are not in the same class the point is made.

Gary

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Ok, I would like to follow the PV theory. I have ridden 2 strokes before that "hit" very hard through the power band. This bike does not do that. It does have more power through in higher rpm's of course, but I can't say that I can tell when the power band hits. How do I test and/or correct if the PV is not working.

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Someone with more experience on the 125/200 needs to step in. I think you can remove a cover on the cylinder and see the power valve actuator move to check it is opening while the motor is running and you rev it a bit.

If you don't get any response you might need to start a new thread with another title, not rev limiter. Something like 125SX no high RPM power.

Gary

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The post on the main jet is a good point, if it's jetted just right and you can hold it wide open without load it will flatten out a little on top(sounds like a limiter) and under load it will clean out and pull hard.Have someone ride it that has an 'ear' for this.

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