I'm all about finding the performance edge. Especially, with these little cars. They need every little bit and every little bit counts. I've gone through full performance tune up on this 600cc 4stroke air cooled wonder. Ignition timing is perfect. Cam timing dead on. New coil wires, new points, new plugs and wires. I'm now sorting the carburetor for maximum performance, here I was trying to richen up the jetting a tad by spacing the main needle. It runs much better and feels "pretty" good, but not "stellar" however. Untill I install a wide band oxygen sensor to precisely measure air fuel ratio, it's just a guess. My wide band tuned 25 hp. 360cc 2stroke Subaru 360 hits 62 mph in the same span as this untuned 37 hp 600cc 4 stroke OHC Honda 600. I need to make some more tuning test runs, I'm not exactly sure, but there has got to be more "umph" to be found. I'm bound to get it.