Re: whats the difference in mercury motors?
If you are really wanting 4-stroke I would say you have some choices, but you really need to know what you are looking to do.
Some of the 25s 4 stokes are two cylinders and 1 carb. Bigfoot is an example of that, but that is a high thrust more intended for sailboats and pontoons. Another example is Yamahas 25 4 stroke.
Other 25s in 4 stroke such as Honda and Suzuki are 3 cylinders with 3 carbs.
Merc has a 3 cylinder with EFI and as far as I know this is the only model with EFI currently available in a 25 HP.
I would say look at weight as a major factor on 25s. The suzuki is pretty heavy at around 212 lbs. I does have more displacement than some of the others to be fair.
Honda and Merc EFI model are pretty similar in wieght. Somewhere around 170 with Tilt & Trim.
The Yamie is pretty light as well, but it is also not as efficient with the single carb and not as smooth with 2 cylinders instead of 3.
What I can tell you about the Hondas. Very smooth, but they do tend to be a bit picky on gas and somewhat cold blooded. Very very small jets that are subject to getting clogged if you are not carefull about draining fuel and using stabilzer. Total pain to fix this. Pull all three carbs with the manifold, clean and resync. Looking at $300 or so. Can't say for sure, but I suspect the Suzuki 25 4Stroke is similar in design.
I know several people with the yamies and they say they run great without a lot of problems. The spark plugs tend to get bad after 3 or 4 years, but that is a very easy thing to fix. My good friend has the bigfoot 25 and that also seems to be easy to take care of and very reliable.
The merc EFI is new, and they are made by tahatsu for merc. Don't know much about them and there is not much history yet. I have talked to a lot of shops about 4 stokes and they all seem to say carbs have small jets and they are a pain to keep running long term. Almost everyone I talked to says go EFI if you can when looking at 4stroke
Now about the 25 HP range. My thought is this is the most difficult range to make a 4 stroke work well in terms of your boat sitting right, getting max performance, and reliability. The boat you are looking at is most likely 400-600 lbs and close to 200 lbs hanging of the back can be a real problem. You tend to come of plane faster and dig in deeper on hole shot. Pain in the butt if you run in shallow water or no wake zones.
Having run both 2 strokes and 4 strokes in 25 HP, I would personally look at either a 2 stroke or the merc EFI.
Suzuki DT 25 2 stroke is flat out reliable 3 cylinder 2 stroke with 3 carbs that can push heavier loads and will get you faster top end. Not real friendly for trolling but not horible. Harder to find than most. Lot of outfitters run these motors and buy up anything they can find on the used market.
OMC 25 is something you know will run a long time, but in my opinion not as much performance as some of the others. Good troller and starter. I am a huge fan of the OMC 15, 9.9 and 6 HP though.
Nissan makes a nice 25 2 stroke and so does Yamaha, plus they are fairly light. Nissan probably trolls better, yamaha is pretty much about running hard.
Merc 25 classic is solid as well, but not a great troller.
My top 4 would probably be (in no particular order):
Yamaha 2 stroke
Suzuki 2 stroke
Merc 25 4 stroke
Nissan 25 2 stroke
Lot of guys will tell you go 2 stroke or go 4 stroke and give you strong opinions why. I would say on a small boat when looking at max HP, be very carefull with weight. When looking at the 25, you are ballpark 50 lbs or about 1/3 more weight for a 4 stroke. Make sure you have somewhere to get parts and service, and try to understand what your objectives are. Sounds like you really want top end, which tend to make me say 2 stoke is a better fit for that not condisering other factors.
The 25 range really has a lot of diversity in terms of weight, cylinders, and such. If you go 2 stroke, you may be limited in what is available new, but there are plenty of good used models out there and I would not be afraid of them at all. Just make sure you look them over real good.
Also, consider a 20 HP 4 stroke if power is not everything. You shed a lot of weight going down 5 HP, and you go to a more basic 2 cylinder 1 carb setup that is likely to be less hassle to keep running well.
As far as clean burning goes, every 2stroke will have some fumes and smoke and the 4 stroke is cleaner. Not sure I would care if I am running WOT most of the time. If you troll around a bunch, 4 stroke may be very appealing because of the smoke and they run quite.
Last thing. Most of the 4 strokes have 25 and 30 that really are close in weight. Specifically the Honda, but also Suzuki and Merc. Merc 30 does grow in weight some from the 25, but not a whole lot. You may want to compare 30 HP 4 stroke to 25 HP 2 stroke in you decision process. 5 HP on a small boat is significant, even more if the weight stays the same.
I had the honda 30 HP on a 615 lb hull. It did the job, but I ended up moving to a 40 EFI. Your boat is smaller, so I would expect you could be looking at top speed around 28 MPH with a 30 HP 4 stroke. Pretty fast for a small boat. Add some chop and wind and you might be going faster than most people want to go.
Good luck picking a motor. Lot of good choices out there, but you can likely narrow it down to 2 or 3 pretty quick when you consider all the factors such as service, availablity, price etc.
