Ok, I am thinking about getting a new exhaust system (full or slip-on), primarily to make her sound like a real bike as well as get the performance gain. Is it possible to get a system and try it out with -no- re-jetting of the carb? Re-jetting sounds like a job for my local shop at $75 per hour; it'd be nice to go with a system for awhile without the "black science" of re-jetting.

Anyone?

Thanx, Lance [8D]

 

Staintune requires no rejetting and is very high quality

 

tennisman - you really need to do the jetting, open the airbox, and drill the slide. While jetting may not be required, per se, just the other day you posted about dropping the KLX250S because you wanted more off-road performance - that's why I'm suggesting to do the jetting - the standard mods, and probably the 13t sprocket too. All that can be done for around $50 or so.

These really aren't that hard to do. By far the hardest part is getting the carb out of the bike in the first place. Maybe you know someone who can help if you aren't comfortable doing it yourself and can avoid having to pay a mechanic to do it? Maybe one of your riding buddies or something? It really does make a big difference.

 

You can install a slip-on and possibly get a performance gain without jetting. As Maverick said, there are companies like Staintune that design their pipes to maximize the stock jetting. However, you won't realize the full potential of any pipe until you maximise your air intake and get the jetting dialed in to correspond with the increased airflow. Even staintune sells a large bore header as an option to go with their slip-ons and I'll bet they don't expect anyone will stay with stock jetting and air intake with that set-up (you could, but what a waste!).

Most importantly, if you run the pipe with stock jetting and decide to do a simple mod. later-on like removing the air box lid, you will ABSOLUTELY have to change your jetting or engine damage will result.

 

Lance I see two other members in GA. ANDY and RON. Send these guys a PM and see if they can be any help.

 

When it comes to the whole air-flow/fuel system (air intake, airbox, air filter, carb & jetting, cylinder & valves, exhaust header, and silencer), I think the saying "a chain is only as strong as its weakest link" is very appropriate.

Each component plays a significant part in converting energy from a chemical state (i.e.: fuel) to a mechanical state (e.g.: wheelies), and furthermore, each component can contribute to that conversion in many different ways (i.e.: there is no "1 perfect configuration" for each component individually). What this means is that each of the components must be tuned in conjunction with the tuning of all the other components to maximize the efficiency of the overall system -- end-to-end, not just individual parts. Yes, you can improve individual components and realize some performance increases, but maximum performance gains are realized when the system as a whole is tuned.

Aside from performance gains, however, is the issue of running too lean (i.e.: the fuel/air ratio is low, or in other words, too much air & not enough fuel). Somebody correct me if I'm wrong, but I don't think performance suffers as much from being too lean as it does from being too rich (i.e.: too much fuel), so running too lean is not as noticeable. The problem with being too lean is that your engine runs hotter and you can damage your engine (warped valves, burnt piston, scorched cylinder, etc.).

As it comes from the factory, the KLX250 is setup to run on the lean side, because it produces fewer emissions, as required by the EPA. Caution should be taken when doing any modifications that would cause the bike to be even more leaner (e.g.: high-flow snorkel, removing the airbox cover, drilling the carb slide, etc.), because this alone could cause the engine damage mentioned above.

Changing the exhaust components without re-jetting is not as serious, because (I believe) this by itself does not change the fuel/air ratio. Some performance gains will be realized, but as mentioned at the start, you probably will not realize the full performance potential of the pipe (i.e.: you're not getting the most "bang for the buck").

Hope this sheds some light on the subject ... and as usual whenever I make a public statement:

Comments / questions / criticisms are welcomed / encouraged / expected!

Mike