I love the little Bird built machines, I've had several and wish I had kept a couple. Originally it would have had a 2.5 to 3.5hp Tecumseh depending on the options, the briggs will be a tough fit with the big tank but the HS50 Tecumseh will fit fine given it's physically the same size as the original. OldMiniBikes warehouse sells replacement brake pads for these bikes, the reason the rebar was added is that those aluminum scrub brakes get glazed over and sometimes fail to stop where you intend. See the "high speed forks" thread in the photo collections section and you will see many Bird bikes with the forks smacked back due to the inability to stop. I would still run one but would add a lever on the bars to actuate a clutch brake which can be easily made for Tecumseh or other 4 bolt pattern PTO covers and they stop on a dime. Plenty of threads on clutch brakes and having two braking options is sweet and much safer for the kiddos.:thumbsup: