switching from 91' 50hp Johnson to 78' 70hp evinrude

[sboyd79]

Hello, this is my first time on here so bare with me if I do something wrong. I bought a 1990 sunbird 15' OB with a blown Johnson 50 hp outboard on it. I have been looking for awhile for a 3 cylinder 70hp johnson or evinrude as a replacement since the boat can take the 70hp max. I have found a good running 78 70hp evinrude and want to replace the 50hp J with it. What hook up problems will I face with this switchover? I know I will be running mixed gas and that's no problem, more reliable that way. I would like to know if I can use the 1990 OMC Johnson controls/cables with the 78 motor, it has the same "big red plug" for the harness. Any suggestions or advice would be appreciated. Neither motor has power T/T, but I would like to have that option too at some point, the control has the hook up for it with the button right on the throttle handle.

(By the way, the 1991 in the title is wrong, the boat is a 1990 sunbird with the original 1990 johnson 50hp on it)

 

[Texasmark]

Re: switching from 91' 50hp Johnson to 78' 70hp evinrude

If the '78 is like the '75 there is a thermostat and no pee tube, nor audible alarm for overtemp. If your stat sticks shut (like mine did one day at WOT) it'll cost you a powerhead overhaul.

So I'd opt for a new stat and impeller before you ever put it in the water.

Mark

 

[sboyd79]

Re: switching from 91' 50hp Johnson to 78' 70hp evinrude

I do have the pee hose out the back of the case

 

[Dhadley]

Re: switching from 91' 50hp Johnson to 78' 70hp evinrude

It's all plug & play. A direct swap, no big deal. Same mounting holes, same wiring harness, same controls.

Welcome aboard!!

 

[sboyd79]

Re: switching from 91' 50hp Johnson to 78' 70hp evinrude

Great! Thanks, that's what I was hoping to hear. I only have one more question, if I wanted to put power trim on the boat, what year unit am I looking for, what size motors are the same as the 70hp when it comes to the power trim unit? I believe from another thread I read I have the type of control that takes a solenoid because I have the 3 wires. So, besides the T/T unit, what else will I need for the system to work? Where does the solenoid mount? I am confused still on the generations of motors Johnson/Evinrude produced and what year bracket 2 & 3 cylinder motors are the same and/or different.