Hello. Several local flyers and myself are using this engine for certain projects and we have all ran into the same problem. We need to use aftermarket mufflers and have gone broke trying to find one that works with this engine. We have bought Bisson , Slimline and JTec. Nothing works but the orginal!!!! The engine runs like crap on all other mufflers. We have tried a lot of things and have found the engine will run great IF we run a pump of some sort along with the other mufflers. What is the deal with this OS engine??? It should work ANY muffler.

Ken

It's not that the engine should work with ANY muffler, but that the muffler makers should make sure their mufflers work with the O.S. engine. O.S. cannot design their engine to someone else's muffler design. Please remember that many muffler makers don't really take the time to work out all the kinks in their mufflers. They basically make a generic "can" and then adapt the fittings so that it will bolt/clamp onto various engines.

With after-market mufflers, you may have to adjust the exhaust outlet to get enough pressure to the fuel tank to give the O.S. Max .91 FX enough fuel pressure to run well.