Hi - I have an os 61 and I was wondering if I could put a .91 muffler on it? I lost the 61 muffler and the only other muffler i have is one of a 91

The 91 muffler generally has more volume so you would probably lose some pressure to the fuel tank. Try it with the nose of the plane straight up for a bit to see if there is enough pressure. It could give a power increase. Adjust the carb needle as needed.

You may lose performance as two stroke exhaust are usually tuned to the diplacement of the engine to assist the removable of the exhaust gasses. Of course, if it fits, it wouldn't hurt to try it to see how it works. I would think the flange would be a different size though.

Don

it worked awesomely!! in fact it kind of sounded cool a little bit realistic

Great.

They are the same muffler except for the extension added to the middle of the 91