I recently just purchased a KLX250S and would like to give it a little more power but not sure what to do. I have read all of the forums but so much info and many people saying different things. I asked the Kawi dealer by my house if adding a Dynojet kit would help power and they said I don't need on just need to rejet after adding muzzy or biggun exhaust. Is this true. I drilled out baffle and bikes seems much better. How much better would it be putting different exhaust. What does putting 13t sprocket help. What is the best way to get the full potential of the bike. I also live in Denver so I don't know if any of the posts woud relate to my situation since most are near sea level and not the elevation I am at. I would really appreciate the input.

 

Welcome to the forum. The dealer is partially correct, if you change the pipe you have to change the jetting. This is also true of any airbox modifications (ie: removing snorkel, removing lid). I would order the dyno jet kit, when you get it jet it as if you already had the pipe (if that's what you're planning on for the near future) and then do the "Grapevine Mods".

As far as the altitude: check here

Don't be afraid to ask questions.

 

What are the "Grapevine Mods". Sorry I am new to this. How much better would a muzzy or biggun be vs. drilling out the baffle. What is better the big gun or muzzy. Could you tell me what it quieter and are they both street legal? Thanks

 

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Muzzy or Big Gun are much preferrable (in general) to drilling. Drilling is free, though. Just about all of us drilled first, new pipe later. Regarding Muzzy or Big Gun - they are both well liked by their owners and seem to be excellent products. You can't really go wrong with either one.

I think the legality depends on where you are since different regions have differnt laws about such things. Both are USFS approved when they have their quiet inserts and spark arresters installed which is important for some areas.

From hearsay, rumor, and inuendo gathered from many sources, the Big Gun is a little louder than the Muzzy. But take that with a grain of salt because to the best of my knowledge no one has actually used a dB meter to measure the sound pressure output of both side by side to say one way or the other.

 

Is there a big difference other than price in getting the slip=on vs. the entire exhaust. Where exactly do I drill out the vent box?

 

Here's the rub with slip-ons. The aftermarket pipes are designed for the KLX300 and while the overall length and shape is fine for the KLX250, the head pipe / mid pipe is not the same length / size as on the KLX300. Thus, the KLX300 slip-ons won't work for the KLX250S with the stock head pipe. But if you got a KLX300 head pipe also, then a slip-on would most likely work with that. Note that a KLX300 pipe exhaust and/or head pipe is also an option and can be found very economically from a second hand source.

When you say drill out the vent box - do you meant the crank case breather mod? If so, that's the thumb sized hose leading into the airbox on the throttle side of the bike from the engine side (front to back). Disconnect the hose, and use a bit and vise grips or similar to drill by hand. Careful about the plastic shavings - you don't want to suck any of that into your carburetor.

If you mean the 1/2" exhaust pipe baffle, just use a 1/2" bit and drill into the exhaust hole through the first baffle.

 

Do you have to modify the carb if all you do is drill out the exhaust?

 

You don't have to, but putting in a dynojet kit or just jetting the carb correctly (it comes too lean standard) makes a fair difference

 

In order to change the sprocket to a 13t do you need any special tools. If not how do you keep the bike from rolling other than applying the break. Which way does the bolt turn and will I need to adjust the chain after putting on the new sprocket.

 

An Impact wrench would make it easier. I haven't replaced mine yet I imagine it turns counter clockwise. The chain may need a slight adjustment.

Cheers

Garry