Swap out newer Johnson for older Mercury?

[Sippen]

Hello, I have an '89 Mercury 70 and a 2000 Johnson 50. The 50 is on my 16' Crestliner Superhawk. The boat is rated to 90hp. I am wondering if it is worth the effort to remove the 50 and install the 70. Both have power TNT and I bypassed the VRO on both. The Merc ran fine when I ran it about 2 yrs ago. The Johnson runs fine, a little rough on idle but not bad. I was also considering looking for a used 90 and sell off both motors. My time on the boat is pretty much all fishing and the 50 can hit troll speeds of around 2.5 so that is a plus, not sure the 70 will do that and if a kicker will be needed (but would like one anyways). I also wonder which motor (in general) is a better built motor. I think the 70 block was also used in the 90hp's so it might be a little more "beefier"? Gauges would also need to be purchased for the 70.
Thanks for your feedback!
Dave

 

[bonz_d]

Boy o boy that's a lot to think about. Just for the fact that the boat is rated for a 90 the 70 would make more sense. Got to be a bit underpowered with that 50. In my mind the age doesn't make a differeance. What matters is how they were used and taken care of. Myself I prefer OMC and have no experiance with owning Mercs only because I do most of my own repairs and the OMC are just easier for me to work on and get parts for.

For the past 2 seasons I've been running an Alumacraft Classic 16 which is rated for a 75hp yet I am perfectly happy running a 60hp Johnson 2 cylinder on it. Has plenty of pickup, planes quickly and trolls fairly well. I also think a 70hp would be squirrely, especially when the water gets choppy. Then also sinse I've purchased this boat I've seen many of the same that are only running 40hp on them. So?

 

[Silvertip]

You don't need any new gauges. The speedometer is pitot driven. Tach gets its signal from the stator so you set the calibration dial on the back to whatever pulse setting is needed. Fuel gauge has nothing to do with the engine -- the sender is in the fuel tank. If you have a temp gauge your Merc would need a sender. Water pressure gauge if you have one can be plumbed the same way as the Johnson. You have Johnson controls so those would need to be switched or adapted to the Merc.

 

[Sippen]

Thanks bonz, that's kinda what I was thinking regarding the jump from 50 to 70, an improvement but may still be "squirrely" as you said.
I also do my own repairs and if the OMC is easier to work on then that's a plus.

Boat is rated 50-90hp and it does feel under powered. It still gets me to the fish, but once while on Lk MI the waves picked up quick and it would have been nice getting off the water a little faster.

Probably just run the 50 until it dies or I find a nice 90.

Any other thoughts let me know.

Thanks,

 

[Willyclay]

Its always nice to have more power available than is required.

 

[bonz_d]

Its always nice to have more power available than is required.

Just cause it's rated for it doesn't always make it prudent.