KPX250 Whistling/Ringing Noise

[rdawg]

Hello all,

I recently got my first motorcycle, a Lifan KPX250, and have put about 300 miles on it. Since a couple days ago, I started hearing a very high pitch noise, and I was hoping someone had an idea of the cause.

The noise starts after a few minutes of riding, but is only present at speeds above about 11 MPH. Letting off the throttle doesn't directly affect the noise, and neither does breaking. The only thing that seems to be affecting the pitch of the sound is the speed of the bike.

The noise sounds very close to what can be heard in the first 3 seconds of this YouTube video, but I already ruled out the gas cap as a cause:
https://youtu.be/KelWjkZSDCI?si=SpJdx1jwmVQml87M

One last thing, I have not noticed any change in the performance of the bike since hearing the noise.

If anyone has any idea what is causing this noise, I would really appreciate the help as I am still new to riding and working on bikes. Thanks!

[zero_dgz]

Being tied to the movement speed of the bike means it is something rotating when in motion, which narrows it down to the wheels, brakes, or chain.


If I were a gambler I would start with the brakes.


Other possibilities include squeaky bearings or the inner race of the same rubbing against one of the axles, or having a squeaky roller (or multiple) in your chain.


And are you sure it ain't your helmet whistling...? The new visor I put on my Qualifier whistles in the wind at very specific speeds.

[mark hall]

Dragging/loose chain/chain guard? Rubbing wheel, rear wheel/chain off center? vibrating plastic/missing screws? Mine is great.. 600 miles now. Did you notice a big power improvement as it broke in?

[rdawg]

Dragging/loose chain/chain guard? Rubbing wheel, rear wheel/chain off center? vibrating plastic/missing screws? Mine is great.. 600 miles now. Did you notice a big power improvement as it broke in?

No noticeable power improvement in the 300 miles I've put on it. Should there have been?

[TominMO]

Very likely it's the plastic chain guard, a known issue. Easy to fix. Remove it, or modify it where it rubs.

[SkyStryker42]

Very likely it's the plastic chain guard, a known issue. Easy to fix. Remove it, or modify it where it rubs.
Are you referring specifically to the guard, or also the guide on the swingarm? I've noticed on mine that the chain guide on top of the swingarm has the notch that centers the chain worn on one side because it doesn't line up straight with the front sprocket.

I also have some noise occuring at speed, and its frequency increases with speed, like brake squeak, but I've ruled that out.

[TominMO]

Are you referring specifically to the guard, or also the guide on the swingarm? I've noticed on mine that the chain guide on top of the swingarm has the notch that centers the chain worn on one side because it doesn't line up straight with the front sprocket.

I also have some noise occuring at speed, and its frequency increases with speed, like brake squeak, but I've ruled that out.I'm referring specifically to the plastic chain guard. As for the guide, if you put a larger front sprocket on, that may help keep the chain off the guide. Max number of teeth for a KPX front sprocket is 14. It just barely clears the swingarm, at the rear of the sprocket.