Just for your information, "Hi" isn't actually the high mark! It's only an indication so you know the valves are moving towards the high position.

As Dave says, make sure the cables are adjusted properly, and also have the required slack in them.

If in doubt as to its operation, I would be inclined to fit the servo without the cables attached (pin the RC Valves open with a knock pin) and run the motor. The servo should move from closed to open at 2000rpm and back to closed at 3000rpm. Once you've ascertained correct movement, then attach the cables and adjust the cables as necessary.
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Andy.
NSR-WORLD.COM

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