Kubota 5 hp ohv mower. (Got two of these big heavy sob's) One of my guys was using it and said it just shut off. Won't start. Got good spark. Got fuel (plug wet when I pull it). Flywheel key is fine. Valves are opening and closing as normal. Compression seems low. Pulled valve cover, compression release device of some kind inside the motor is bumping intake valve when I turn motor over like I assume it should be- or shouldn't it be? Is it stuck? How do I fix this? Wish I never bought these things because the clutch for the blade is a PITA & they weigh like 5000 lbs & so far haven't been more reliable than a $99 cheapy. Thanks.