Hello, I em looking to purchase a .61 os 2 stroke with a Bisson in cowl muffler from the local hobbie shop and the owner of the shop said he could give a great deal on a 4-stroke XL .91RFS engine for my plane. (GP 300s extra) Its a new one right out of the box never been run. He said it's been sitting there for a while an that he would like to sell it, because this one isn't a popular seller. I can get it for $120.00. I never owned a 4-stroked . My question is , is this engine a good runner , easy starter, easy maintenance, and is it a good choice to purchase. Also if it is, what muffler do I use for mounting inside of the cowling . I Have 2 planes with OS 2-strokes .40 &.61. I would like to hear from people that has had experience with this engine good or bad . Thanks for any replies