Which part is "dumb"?
There is no replacement for displacement, and In my experience the 351 kit made a large difference in power while my installation of the FMF Q4 about a year earlier made a much smaller difference. There are quite a few on here ( guessing 99% )that will say the 351 is the single best mod they have done.
Dan

 

The 351 mod was the best thing ever, and the bike should have been sold as a 350 to start with. it really is an easy project as long as you have the proper tools and a manual.
If you don't have the skill,, pay someone. you really really really will like it. forget the pipe for the time being.

 

Back to the OP's question...
I picked up a "slightly" used HMF slip-on from ebay for about $120. It was advertised "with one small scuff." Now it has several more .

 

Be very careful with free mods to the stock system. The only thing worse than a loud pipe is an illegal pipe that has had its spark arrestor disabled by some hack trying to make it louder. Spark arrestors are important and required.

I would love to find an OEM KLX300 exhaust if it fits our new gen KLXs. Factory quality muffler and no packing to replace. Replacable but plugs for variable sound/performance levels.

I like quiet but the stock exhaust makes the bike sound like a stupid sewing machine.

 

I don't ride where spark arrestors are required, so its a non issue for me.

Besides, mods like mine retain the factory spark arrester if i hadn't already drilled it out like an idiot before hand.

 

Might not be the best option, but for now it really woke up my stock 2007 klx 250. I replaced the stock 250 muffler and header with a full 1998 klx300 exhaust I bought off eBay for $75 shipped. Everything bolted on perfectly within 10 minutes I did not have any fitting problems. I now have the option to remove the butt-plug, (thinking of putting on a turn down end plate with plug removed). You have to get the whole exhaust as a 300 can will not bolt onto a stock 250 header. I then did air box mod, carb rejet, and put on a 13 tooth front sprocket. All of this around $150 (dyno-jet kit, sprocket, full 300 exhaust) and am very pleased with the result. This is just a starting point as I will eventually do a big bore kit and better exhaust, however, for now I am just enjoying the new power (very noticable) and sound. There are a lot of options but I feel I did the bike some justice for a little investment. Good Luck!!

P.S. when you do your carb don't forget the kouba link fuel/air screw. It will make life easier as you adjust your mixture.

 

mega bomb and powercore

 

yeah but with the 351, u go different air box, jet kit for the carb, headers, etc... right? Its not just drilling out the enrichment jet for starts, taking off the cali crap, jetting, and doing an exhaust. The klx is a terrible commuter unless you mod it, my head hurts after ripping it on the highway at 75 (with the wind blowing). You want cheap mods, do the full exhaust, jet it, and change front sprocket..... anything else... its probably not worth the cash...

 

Air box is the same and you can use all the stock parts with the exception of jets with the 351.

Bill's big bore is bar none, the cheapest (for what you get), most significant upgrade you can make to these bikes.

 

Hey I have a used 2-Brothers slip on that I will sell you. it was used for a week then I sold the bike, will also give you a set of aftermarket mirrors. Both the pipe and mirrors are in Excellent condition....e-mail me for more info @ cop1071042@yahoo.com or call/text me at 479-957-8810. i can send you some photos..... oh for more info on the pipe go to 2-Brothers racing web site for HP gains....ect....thanks Curt