I've been reading as much information as I can over on a KLX300 forum. They all seem to go with replacing the head pipe and keeping the muffler.

I have not looked specifically at the muffler on the KLX300, but on our it kind of look like some of the model airplane mufflers I've played with. The outlet is so small.

The head pipe looks like stainless steel. There seems to be two pieces to the muffler - a pipe from the head pipe to the muffler and then the muffler.

Head pipe diameter, while not huge is not that small. Looking at it and the header (Akrapovic) on my ZRX make them out to be about the same diameter. Should be sufficient.

Perhaps a muffler is the way to do. H'mm, there is a Cobra on the KLR250, it might migrate one of these days. I'll let you know.

 

I've been reading the same stuff. What I'm concerned about is the fact that the headers seem very different between the 300R and our bikes on the parts drawings including having the header bolts be vertical vs. horizontal in the head.

 

I think for me I don't really want to mess with the bike too much, but I am interested in this drilling of the airbox that I have heard of. but if you also have to match the air with exhaust upgrade then I'll leave it alone.

On my 99 Dodge Cummins Diesel 4X4 I added the K&N air filter, and it really made a difference, now if I could only afford the 4" exhaust.

deej

 

If I decide to keep the KLX250 longer than a few months, I'll use the Dynojet kit for the KLX300, K&N air filter for KLX250/300, and I'll put on the Big Gun EVO X full exhaust system (says for KLX250/300) -- my mechanic syays they will fit. The collar is supposedly not fixed -- it can rotate on the pipe to fit the bolt axis. So said the mechanic, but he could be wrong.
The part numbers for the header pipe are the same, for the 2006 KLX300R and 250S on the Kawasaki site parts list, so if the collar was fixed, logic suggests the collar must be moveable.
We shall see.....