I have a late 80's 8 hp mercury outboard. The motor only has around 30 hours on it total. It starts and runs fine. Goes into gear smooth. But when I am about half throttle it kicks out of gear back into neutral. Reves up high and I have to turn the motor off. Clutch dog???/ Any ideas would help.... No shifter on the motor it is all done within the tiller arm from back to forth!