I have run and/or owned/had all of the following:
ETEC 25
Yamaha 4 stroke 25 (98-06)
Yamaha 2 stroke 25 (twin carb model, 3 cylinder model, and the old single carb models)
Merc 25 (2 stroke)
Merc 25 4 stroke (tohatsu)
Mariner 25 2 stroke. Same as Merc 2 stroke.
Tohatsu 30hp single carb twin cyl.
Yamaha F15 (4 stroke)-both early and later models
Yamaha F25 (2008-2015 4 stroke)
Suzuki 15hp 4 stroke (2014)
Yamaha F15
Yamaha 15 2 stroke
Yamaha 9.9 2 stroke and 4 stroke both
Yamaha F20 (4 stroke)
Evinrude 9.9 and 15 2 stroke, mid 80's to the early 2000's.
Johnson 9.9 and 15 2 stroke up to about 1995.
Evinrude/Johnson 7.5 2 stroke
Yamaha F40-all year models and configurations
Yamaha 50 tiller (2 stroke)
Yamaha 70hp 2 stroke. Also an F70 at one point.
Yamaha F115 TILLER (that was a handful)
Yamaha F40 jet, 2014 and a 2012 model-same motor
Yamaha F150
Yamaha F250 on a bass boat
HPDI 225
Those are the ones I've run that I can remember. I know I left a couple out.
For this discussion I assume we're talking about 40hp and below being that your boat is a 1648. If you're rated for a 40hp, I'd go right to 40hp for a lot of reasons, if the budget can allow. Having run a few 40's, both 2 stroke and 4, my personal preference is the 4 stroke Yamaha. Expensive motor. But worth it in the long run. Higher resale. Silky smooth and honestly nearly silent. They are not racing motors; and I think people have too much expectation when buying them-those are the guys who get disappointed with them. Especially the duck hunters/boat racers. My second choice would also be a Yamaha, but a 25. The 4 stroke 25 is nice, and new ones are still relatively inexpensive, but real heavy-and that is the only downside. They come with tilt assist now which helps a "ton".
I have run the ETEC recently, finally. Was not impressed. It is 2 stroke. It doesn't have poppet valves like a 4 stroke does. But it has a high pressure fuel pump, high pressure injectors, all the electronics to control it all, a charging system that is a little inferior (some of the charging system capacity gets eaten up by the hungry EFI). Also, it's heavy. One I ran was a long shaft electric start with PT. It did not have trim that I know of. It would tilt but under power, more than about 25% throttle, it would not tilt. About 165 lbs I think they are-which, IMO, negates the reason for having a 2 stroke to begin with (weight). Also, if you have it tuned to run Evinrude's specific 2 cycle oil and for some reason you want to run some Quicksilver-or any other brand-you have to have the ECU re-flashed. So if you're on a vacation and run low on BRP's oil and no dealer within a hundred miles radius, you're out of luck. At least that's the impression I got from a dealer. They say it's no big deal. That's a big deal to me. It is a 2 stroke, and there are some die hard 2 stroke guys left out there, and no disrespect to them at all. Everyone has their own preference.
The suzuki, I actually liked it but it was propped incorrectly (overpropped). It was a slug out of the hole and took forever to plane. And only ran 4300 RPM wide open. It was the factory installed prop, on a War Eagle 436, which is a decent hull (and not real heavy). 18.6 mph max. It needed less prop, but other than that it was ok.
Rest of them are more or less old school, which most are already familar with.
The 2 stroke Yamaha twin carb twin cylinder motors are hard to beat. Light. Fairly fast. Low maintenance. Old school carbureted motor. 11 1/4" factory prop is spot on for most hulls and should net about 27 mph.
Yamaha single carb 2 stroke 25 was more or less a 30hp motor with timing differences. It ran great but it was noisy, idled rough, and smokes horribly. Commercial 25 I call them. They were simple no-frills motors and it showed. Almost identical to the early mariner 25's.
The Yamaha triple (3 cylinder) 25hp motors are the hotrods. In stock form with the stock prop, expect to see 28-29mph. Same powerhead as a 30, with minor differences. Many have been modified. Some guys are getting nearly 80 hp out of them; and running 60mph duck boats. Pretty sought after around here.
The 50 tiller was on a War Eagle 548. Way too much motor for that boat. 34 mph max. I was not impressed with it. PT&T and it was on a CMC break-a-way, raised 2.25". It's been reliable-owner is a friend of mine-but it doesn't really run like it should, for some reason. Maybe propping and setup combination, he didn't do much with either one.
F115 tiller--I rigged that one many years ago and had to lake test it. It takes both hands to hold onto the thing and even then it was dangerous. I hated it and my arm hurt for several days afterwards. Guy who owns it is much bigger than I am and apparently it don't bother him.
The mercury and mariner 25 had the forward-reverse shift in the throttle grip. Kind of neat if you had to change directions a lot while holding a spotlight or something. Little interesting to work on. Only bad thing about having the shifter built into the throttle is that if the motor is flooded, you can't really throttle it up to clear it out. If the carb isn't spot on, you can't throttle it up much without shifting into forward or reverse. I never did like them personally but again, to each his own.
