Recently acquired a 2006 KLX250 and I'm working through the free and not-so-free mods. I have a Uni filter, KDX200 snorkel, Dynojet kit, and EZ-Just screw on the way, and I have been looking at aftermarket exhausts (FMF, Two Bros., DG, etc.). I decided to just mod the stock air system for now and see how it goes. Removed the backfire screen for a start and I wanted to open up the muffler on the cheap. Here's the mod, cheap quick and dirty...just like I like it.

Stock outlet:
klx_pipe_zpse206d59f.jpg?t=1401390041

Carve out that tiny outlet and wrench it out of the interior baffle:
2014-05-28215110_zpsa6995ce9.jpg?t=1401390049

Clean it up to about 1 3/8", flare it slightly and tap for screws:
2014-05-28221302_zps3f5279b7.jpg?t=1401390058

Finish it off with a chrome closet rod flange (Yeah, you read that right) - 6 bucks, decent chrome, drilled for mounting, available at any Home Depot:
2014-05-28222904_zps8efbe873.jpg?t=1401390069

I'm open to suggestions for how large a Main Jet to install. I was thinking of going with a 128 so I have plenty of rich-side avaialable and I can dial in my mixture for altitude changes with the EZ-Just screw. Stciking with a stock pilot jet for now. I'm in Washington state and home is almost at sea level but I ride and hunt and fish anywhere from sea level to over 6000 feet. We regularly re-tune our chainsaws for altitude here by ear along with a tachometer but the 4-strokes might be a bit more touchy. I know there will be some opinions on this!

 

So you removed the spark arrestor?

 

as long as you dont drill down into the muffler the spark arrestor should still be ok. its not a screen, its a swirl shaped metal baffle that spins the exhaust gas so the heavy "spark" particulates are trapped insde of the muffler body.

 

i left the internal baffles in place, so the spark arrestor is unaffected. only thing pulled out is the short outlet pipe shown in the second picture. Seeing how that is installed shows just how much restriction is in this muffler design - poor bike is strangled by the exhaust! i may neck the opening down slightly depending how it reacts to the new jetting and how noisy it is. 1 3/8" is a pretty generous opening.

 

Is that what they have been selling on feebay all along?!? Closet rod do hickeys!

 

Motorcyclist ingenuity. It would be interesting to see if there is any performance increase.

 

Just opening the muffler up hasn't really done much except give the bike a new tune - when I get all the other improvements in place it will definitely help to have this breather open. The closet rod flange as muffler tip is just a nicer look than a carved out hole (on the cheap). I mod mufflers on chainsaws and re-tune for the change in pressure/back pressure + altitude regularly and it makes a huge difference in throttle response and overall power. Same deal, just 2 strokes vs. 4 strokes. Haven't found a tiny closet flange for a chainsaw muffler yet though...

 

I did this exact mod last year( and probably many did it before me) Never changed any power levels just the tone of the exhaust. I ended up putting on a DG O series muffler and it made a big difference

 

This mod has been done for years, and as far as I can recall that's the same response from those who've tried it. More noise without any performance gain.

Nice use of the closed rod hanger. That certainly looks better.

 

Yeah, I don't expect a performance gain without changing what happens before the muffler, which is why I am changing air filter, backfire screen, crankcase vent & smog crap, main jet and needle, then tuning the mixture accordingly. But it stands to reason if you do all those things without opening up the final exhaust outlet all you'll get is a lighter wallet.

I have my eye on aftermarket exhaust/header combos. How has the DG performed for you? And did you put a bigger diameter header pipe on too?