Hustler Raptor 42" with Kawasaki FR651V engine. When I pull up the blade engagement knob, there is often a delay before the blades engage, anywhere from a brief moment to upwards of 20 seconds. It doesn't happen every time, but tends to get worse after mowing for a while. The blade belt is not slipping on the pulleys. Otherwise, the engine runs fine, and once engaged, cuts fine. Any ideas?