The X in the OS-CV-RX means it is a pull starter. OS CV-R has no pull starter and you need a starter box. If you are going to get one get one with the standard threaded shaft and all your old stuff like flywheel will fit. The OS TZ has way more power and is a great drive train tester and if you do not have everything up dated and dead right you will not run long. In my opinion the OS CV-R or RX is the best all around engine for the MT.