I have an 05 lowe console steer with  small 4 stroke merc carb engine 20hp, thinking of switching to a little larger yamaha. Question is would old cables hook up to yamaha and if not whats all needed to switch.

You would need to get the forward controls for the Yammie

Just about anytime you change brands, you usually have to change control boxes and cables that match the brand you are going to.  On some occasions, just going to a different motor in the same brand requires changing everything..

Sometimes you could get away with changing the cable ends that go on the motor and a cable adapter, but don't hold your breath while you are trying find something.  Most have gone away from making that possible. 

Thanks guys,  did some checking found i would need to spend at least $600 in parts to make switch. Let alone buy the motor.  Thinking ill stay with what I have for awhile longer.

 

In years gone by, I have twice bitten the bullet to sidestep a Mercury outboard.

The first time (many years ago), I replaced an existing 4-stroke Mercury with an Evinrude Etech.

More recently (2 years ago), my wife & I rode from Florida to Kansas in order purchase

a Yamaha-powered Alumacraft. Why would such foolish trip be necessary?

Because Mercury implemented a shrewd & monopolistic squeeze on the boat hull industry.

 

Roger

I doubt Mercury made your 4 stroke engine. Look into who is the original mfr. 

Tom