[Johnny 5]

I have two fmf 2 stroke universal mufflers on our dune 155cc and 183cc and they were loud with the large 1 1/4 opening. So I used the tubing that came with the muffler kit and made a turn down tail pipe. It was quieter but still crazy loud and lost power even with jetting the carbs up. The aluminum rivets that I used to attach the tail pipes failed in the first hour and I had to remove them. But we were at 3600 to 4000ft altitude and we usually ride at sea level in the low desert. I ended up welding the turn down tail pipes and adding a 3/4 inch tail pipe welded to a washer and then welded to the inside of the turn down pipe to get some back pressure and it works great and is a lot quieter.

If I could do it again I would get the 4 stroke muffler due to the larger size and baffling inside. Also these mufflers get hot compared to the stock muffler. The fmf stickers are baking off but it got us to ride at a different place were usfa spark arrestors are required and it was worth it.
The 1000.00 dollar or more ticket for no spark arrestors is the only reason I changed the mufflers. The stock muffler with a 3/4 inch tail pipe worked great on our buggies. Not enough back pressure is bad for low and mid range power.