Honda reble 250 cut off muffler to add horsepower?

Cutting the mufflers off of a motorcycle's exhaust system is not the BEST way to add power. You would also need to change the air filter to provide for greater intake. Though you may gain a small amount of power by doing this, you will also completely alter the bike's air/fuel requirements. This will require re-jetting of the carburetor. Without re-jetting, the bike will run way lean, and burn the exhaust valves, and there goes your compression (and you will ultimately end up with no power at all). If you really need more power, get a bigger bike. If you're into Hondas, you can pick up a Shadow 600 relatively cheap, and you'll have a lot more grunt. Always be SUPER cautious when making modifications to any type of vehicle.