Thanks for the info I was struggling with the same problem when trying to order from Australian vs US manufacturers. I don't want to hijack the thread but I have a related question;

09 'Aus spec' klx250s. Looking at full system or just a slip on. Is there any benefit in the full system with new header, as I assume it would be the same diameter as the original?

I know some aftermarket headers have the expansion chambers etc, but the Barrett's I'm looking at is a straight diameter with a slight taper at the exhaust end, therefore is the original actually restrictive?

As well as the extra cost of full systems I really don't want to lose that nice heat shield for a shiny SS pipe and no performance. Learnt that the hard way a few weeks ago on a ride with a mate when I swap for a few miles on his ktm450 and managed to destroy the right leg on brand new par of fox warterproof pants

 

Well, you may get some different opinions on this, but I wouldn't run the stock muffler or header pipe. The KLX250 is pretty anemic, and a good part of it is the exhaust. The larger aftermarket headpipes coupled with a good, less restrictive muffler provide increased power and response across the board when you give it a bit more intake volume with a bigger snorkel or airbox lid mod. If the KLX had the starting power and response of the WR250R Yamaha, then I'd say you could get away with a stock KLX. Otherwise the stock KLX is a weezing wimp if left alone.

I've been seeing some of these comments about the lack of a heat shield on the performance pipes on the KLX. I'm not built like a circus clown...midget or giant...and I've never had an issue of touching the header with my leg. Last month I even crashed on a big uphill out in Moab with the bike falling right on my right leg and pinning it there for a few seconds. My riding pants are plain-Jane Moose models that have a lot of polyester in them but still don't melt or let the pipe burn my leg easily. What the heck kind of disposable, plastic pants are some of these guys wearing, or how the heck are they positioning their legs on their bikes. My Muzzy header is huge, but it's practically unnoticeable when riding...and that's without any heat shield.

 

I run an AUS spec 07 250R with the stock header and a Two Brothers slip on. Drag race with NeilActions 06 300cc kitted 250R, with a Big gun full system ad BB pumper carb. There was very little in it. My motor runs very sweet. The header is too much $$ for a piece of pipe! Put the money into some other mods, petrol or tyres (for AUS riders Torpedo7.com has Pirelli tyres on special this week, half price. I just bought 4..)

And FWIW. The 94 KLX250 D and E series bikes had the same header as the current AUS bike and made 23.5 KW (32 horsepower.) Header works fine for the motor.

 

Not quite. With regards to the U.S. bikes: the diameter of the header pipes is the same for most of their lengths, but the end of the 300 header steps up to a much larger diameter where it mates to the muffler. It is this diameter difference that precludes mixing (U.S. model) 250S headers with 300 mufflers, and vice versa.

 

I'm talking about 250 'mufflers' not headers. The 250 muffler will fit both 250S and 300R headers. I think you read the post incorrectly. It's already been pointed out many times that the 250S (USA) header is shorter. I'm just adding some clarity for those that own a bike with a 300R header.

 

No, it won't. It's not the pipe lengths that's the problem. It's the pipe diameter at the header/muffler joint. The inlet diameter to the 250 muffler is much smaller than the outlet diameter of the 300 header. The 300 header outlet is ~1/4" (~6mm) larger than the inlet to the 250 muffler.

For the record, I replaced my 250S (U.S.) system with a complete 300R system. The 300 muffler will not mate up to the 250 header, even if they aren't on the bike.

 

OK. I see the issue. I was commenting on aftermarket mufflers, I failed to mention that. Lets clarify that. No one wants to replace their 300 muffler with a stock 250 muffler do they?

 

I really don't think anyone would.

OK, for clarity. My comments are all pointed at mufflers that are intended as U.S. model specific "slip ons" for bikes with stock headers (as well as aftermarket headers that are intended to fit with stock mufflers).

1) An aftermarket muffler intended as a slip on for a KLX250S will not be compatible with a stock KLX300R header.
2) An aftermarket muffler intended as a slip on for a KLX300R will not be compatible with a stock KLX250S header.
3) If an aftermarket header is a direct replacement for OEM and will work with the stock muffler for that model bike, then 1 and 2 above apply.

Aftermarket headers will throw a wrench into the works if they're part of a complete system - as they may or may not be compatible with the OEM parts. Best to ask the manufacturer.

 

We'll have to agree to disagree!

The finer points of the muffler/header debate have been discussed many times, sometimes to epic lengths. A search of "muffler king" will enlighten you to the topics that were covered. Where is Iowaguy when you need him??

 

Oh boy I don't think we want to go that direction!

Anyway, I did misread (or under-read) what you said about 250S mufflers (after a trim) fitting 300 headers. Thereafter, I also glossed over your point about your meaning aftermarket mufflers (didn't miss it, just blew over it). Sorry about that.

I think I can see now how aftermarket 250S mufflers may fit up with the 300 headers as a workable solution. I'll just leave it there...as in OK, I'm a believer.

There...dead horse beaten.