I'm looking to replace the stock pipe/silencer on my 400ex, but don't want anything that will be too loud. I would like to bump up a few horsepower, but the places I ride won't allow anything too outrageously loud. Any suggestions??

 

I HAD THE SAME PROBLEM WITH NOISE AND I TALKED TO A GUY IN CALIFORNIA THAT TOLD ME HOW TO MODIFY MY STOCK MUFFLER TO GET THE SAME HP INCREASE AS A NEW SLIP ON MUFFLER. YOU MUST REMOVE THE QUIET CORE SILENCER FROM YOUR STOCK MUFFLER AND WELD THE SPARK ARRESTER BACK ON. THEN YOU CAN EITHER CUT A HOLE (2" X 3") IN YOU AIRBOX LID OR RAISE IT UP USING THE HOLD DOWN CLIPS AND REJET THE CARB. I CUT A HOLE IN MINE AND WENT FROM A 148 TO A 158 MAIN JET AND TURNED THE FUEL MIXTURE SCREW IN ABOUT A HALF A TURN. BELIEVE ME YOU WILL BE ABLE TO TELL THE DIFFERENCE. ABOUT 5 HP ON THE DYNO TEST I SAW.