Re: johnson 125 vs. merc 100
All of the Johnny/Rude V4's are in the 300 to 350 lb range depending on whether or not they have tilt and trim. Most fall in the 325 lb range.
I have a 1995 Merc 115 that weighs in at 360lbs, and an earlier 1978 Merc 1150 that weighs in at 306 lbs.
I don't see a 100hp for 1978, but they did have one in 1988, in that case it would be in the 340lb range, slightly more than the earlier Johnny/Rude V4s.
Either way, if 40lbs is a make or break amount on your transom, I'd have to seriously think about what I'm doing.
Being a bass boat from that era, you probably don't have much freeboard when it comes to adding weight.
If your boat is a 1979, how did it come new from the factory with a 1970 Evinrude.
Weight wise you shouldn't have a problem either way,there's little difference in weight between the 85HP and 125HP V4 motors, they are all basically the same engine with minor differences. Model numbers for those motors will better ID what you have. Even in 1979, I can't imagine a boat builder putting a 125 on a boat rated for 85hp.
I run a 135 on a boat rated for 120 max, but there's little to no difference between the two motors, in fact, I think the later model 120 feels stronger than the older 135 and the later motor weighs in at almost 40 pounds more with the tilt and trim unit and oil tank and hoses. My boat is old enough that it don't have a coast guard plate and I've been boarded for a safety check with the larger motor and it passed just fine. I have an 85hp V4 on a 16' aluminum boat that is actually running a 90hp power head and carbs. I had two motors, one good lower and one good upper and combined them. There was no way I was not using that motor for a 5hp difference and zero weight difference. I never even consider opening it up all the way anyhow. That boat would do just fine with a 40hp, but I already had the V4 so on it went.
The 1995 115 I have is actually lighter than the Johnny/Rudes but feels heavier when moving it around due to it's added height and size. In reality it's only a few pounds heavier.
While it may not be right, I have seen a good number of motors around here with the model number plate popped off and the motor decaled as a lower hp.
In my opinion, so long as you are not overloading the transom and the larger motor is of the same design and weight, the ability of the boat to withstand a larger hp rating is up to whom ever is driving. On my boat, I had never even opened up the original motor let alone the 90hp on it now. There's just no place to do so where I fish. The same for my larger boat. With todays gas prices, it's slow and steady and save as much fuel as I can.
I do find that the larger motors run better at part throttle and burn less fuel doing so compared to a boat that has barely enough motor to get the job done.
