I installed repaired a water pump for a four stroke 40 HP outboard. When conecting the shift rod to the lower unit their is a threaded coupling that attaches the top and bottom of the rods and a stop nut. How do you adjust this so the forward gear engages and yet you have netural and reverse. I have tried serval different ways but somehow am not getting it right. The Service manual from Yamaha is usless on this they expect you to know how.