I lost my muffler of a Surpass 91 today...the thead in the head was worn and no amount of tinkering would fix it. I even put in a grub screw to try and secure it but no luck. It ran fine without the exhaust and another guy at the field said he ran a four stroke for 2 years without a muffler with no problems. Any comments would be appreciated as my last option is to get a cylinder head and new muffler which is expensive. The engine is in a 4 star 60 so there are no venting problems to overcome as the engine has no cowl. Thanks.