I am rebuilding my frozen heat riser system. The vane blocks off the last three cylinders' exhaust and routes it thru the heat riser block under the carb. How much preload in the cold state should the thermo spring have? I can push with my finger through the manifold on the vane at its closed position, should there be a firm resistance? Just trying to gauge how firm it should be before I reassemble. It opens up with some heat from a heat gun.