Here I would simply take the lower unit apart for inspection , repair as needed and re-assembly.-----No manual needed and no need to buy any parts.-----These units are simple , well engineered and reliable.----Your location ?
Pull the flywheel.-----Inspect anti reversing spring.----Inspect drive key on bottom of rotor.-----Motor is always in FOWARD when not running.-----With 12 volts applied to green wire it shifts to NEUTRAL after just 1 turn of the flywheel.
Just make a simple tester.----2 pieces of wire glued on carboard.-----A 3/8" gap between the wire.-----One end in a plug boot.-----Other end clipped to the block.
The new style 7.5 HP came out in 1980.-----Then marketed later as a 6 and 8 HP.---Sweet running motors.-----Often ruined by folks who do not know how to operate / maintain a 2 stroke motor.