1980 KDX 250 Exhaust pipe vs a 79-80 KDX 400 pipes fit

[Mx360guy]

Hi KDX riders,

I am gathering parts for my retirement project, a 1980 KDX 250. The pipe is rusted out and I need to replace it. I found a KDX400 pipe on eBay that looks pretty good.
Would anyone know if a KDX400 pipe would fit the 250 bike?

Thanks and Happy Holidays to all.

[SpruceItUp]

Sounds like a fun project!

I'm not too sure whether or not it would physically fit, but a thought to keep in mind is that it may not perform as it should with a 400 pipe on it, given the dynamic between the size and shape of a 2 stroke pipe to how it makes power.

Best of luck!

[JimmyB]

Found this, few dings/dents but repairable.

https://motodobson.com/kawasaki-kdx250- ... n-chamber/

[Mx360guy]

Hi Spruse and Jimmy,

Thanks very much for the tips and links. I have an '73 Yamaha MX360 and the MX250 pipe is the same. Hoping the KDXs were similar. I guess the tech had changed enough by 1980 that pipes were MFG'ed to create the power for per the CC's, etc..
Thank you!

[JimmyB]

The 2 pipes do look very similar but I would be concerned about the exhaust port size(bigger) and the upper cone/baffle section on the 400 pipe, it looks a lot longer on the 400 pipe.

Some information on how the design of a pipe works

https://www.dragonfly75.com/motorbike/ECtheory.html