Re: Let's Talk Big Twin/SpeediTwin
The '69 - 76 models are basically just a hopped up 20. They have a different head and exhaust system and a larger carb. They weigh about the same as the 18's and 20 and are the same engine block. Of course, this doesn't mean take an 18 and make it a 25. There are a few mechanical differences in the design to get those extra ponies. The 25 is also rated at a 5500 RPM rating, versus a 4500 rating, like the two others. I think the 1972 vintage Evinrude Sportster 25 is a pretty nice motor and would be one of my top choices for a stern drive tinnie. The old 25's are tough old motors, but they're heavier and much better with a remote control set up. Pull starting them is fine, if you have a size 19 neck and size 1 hat. The smaller 22 cube models start a lot easier by hand and are a more common choice for your set up. Not only that, getting one with a tiller handle is standard. the '57 - 58 models are the best in quality. No plastic parts and you don't have those troublesome rubber mounts that typically break on the fiberglass hooded type. Beaching the motor is also better on those old clamshell type motors too, because the fiberglass hood can sometimes come off in your hand. I have a 1958 Johnson 18 that is on my "to restore" list. It looks rough, but it's a factory electric model, with the starter and electric choke, so I can go remote or stern drive with it.
1977 and later 25's were a completely different design and quite a bit heavier than the 22 cube models. The later ones are about 33 cubes, which is almost as big as the 35.7 cube of the 1950's vintage. In my oppinion, I like the 50's vintage 25's because I like the old iron. If you're going to get the 55 Big Twin 25 though, you may as well step up a couple years and get 10 extra horses and only add a few pounds. The '57 35 was a 40.5 cube motor, but has the same cover, midsection and lower unit as the earlier 25 (with the exception of larger gears) The '56 30 was the same engine as the 25 but I think it too had the heftier gears.
