2000 VX225TRLY - can't find any solid information about these. Parts diagrams only list a "nipple/hose" at the reed block and cylinder. Are there in fact, check valves on this motor? I've pulled hoses at the cylinders on 4 and they all pass air both ways. Can't imagine I have 4 out of 6 bad but anything is possible. Still hunting down fouled plug/s problem. Ideally, just need to know if there are check valves or just pass-through nipples as outlined in the pic below.