1971 80 hp Mercury outboard lower unit

I purchased a newer lower unit for my 80 HP merc outboard and have a couple of questions.This lower unit fits and works (in the Driveway).I installed a new impellar gaskets etc. When running on Muffs at Idle the tell tale just dribbles,and when I throttle up I get a good stream,I use to get a good stream with the old lower unit at Idle should I be concered?As for the next question on this newer lower unit there is a black little hose that comes out by the shift linkage whats that for??
Thanks Guy's
Hey Jeff, if you happen to read this I lost your e-mail address

Re: 1971 Mercury outboard lower unit

The little hose is for a speed-o. It should have a good stream all the time. You replaced impellar gaskets, did you replace the impellar, and what did the base plate and housing look like?

Re: 1971 Mercury outboard lower unit

Okay black hose for speedometer,and yes new impellar.I will test it at the lake on the trailer and see if it's any better.If not I will take the lower unit back off and check.Thanks

Re: 1971 Mercury outboard lower unit

Took the lower unit off and found some gasket material in the water pump channels.Have no Idea how they got there but I assume that was the Problem.Fixed.Does anyone know approximately what year they started putting the speed-o hose on these lower units??