Thanks for the responses. Since I have a spare 250 muffler I will do some exploratory surgery. See where that leads me. I have been keeping an eye open for a 300 system in my area but no luck so far. Zomby woof I will keep your guy in mind over the next couple of weeks if this doesn't work out. Must ask, do you guys ever sleep? 4:27AM??? Shift work I hope. Thanks again, some very interesting reading.

 

I have a muffler from the older KLX 250 model. It has the same numbers stamped on it, as the KLX 300 muffler. It's got the removable end cap as well.
I suspect the late model 250 muffler is the same, under that welded on end cap. Probably done to have a tamper proof, noise compliant unit.
Perhaps I'll drill a couple exploritory holes in the end cap of my stock 250 unit, at the 6 & 12 O'clock positions, and see if the end cap screws are visible behind it.

 

There was a guy who cut the stock muffler in half and posted pictures. It was either dirtrider or thumpertalk ...I think

 

OK, so I have completed the surgery and I believe I have accomplished my goal of letting my 351 breath better while maintaining a stock appearance and only slightly changing the exhaust note while still not drawing any unwanted attention. What I have done is cut the end cap off, drilled out the first baffle above the existing tip, added a second and slightly larger pipe and welded them together. I drilled more holes in the last baffle only and re-welded the end cap. To hide the now 2 exits I welded a 1 1/4" tip on to the end cap. As you may notice in the photos, the second baffle has slots cut in it. I left this intact as I didn't want to change things too much. Seat of the pants tells me it worked well. Snappier acceleration and just slightly throatier sound. I think my jetting was a little rich before mod as Bill jetted it for snorkle removed and slip on installed.

 

Short video clip of new & slightly improved (not much louder) exhaust note.
https://www.youtube.com/watch?v=MQ62...ature=youtu.be

 

I've seen it done on another site where they used an 1 1/8 inch holes saw and then removed the back baffle. Then put a 300 klx end cap on. Do you think this would work as well? Your thoughts?

Thx Kevin

 

Sure would work but I bet you would have to contend with lots of extra noise. My goal was to keep it quiet and just open up that pea-shooter to let it breathe a little better. Seems to have worked great but no Dyno to compare power. Butt Dyno says worked well.

 

Man that looks good! My 2 bros is pretty darn loud, gets annoying... Did you do the welding yourself?

 

The removable stock KLX300 end cap is the major restriction in the exhaust system. The hole is smaller than my little finger. Folks have opened it up and welded a much larger "tail pipe" that has a bend in it so the exhaust is directed down.

Ride on
Brewster

 

Would you happen to know, or any thoughts on, how a 300 header and exhaust, that's opened up at the end, would perform compared to a slip on? Would it be roughly the same flow or still much less than a slip on?