Johnnyrude 25 2 strokes?

[matt167]

I've been thinking hard about putting a brand new ~$5k motor on my little boat I'm building ( Suzuki DF30A is on my wishlist ).

Being the boat is going to cost a bit to construct and I'd like to get it under power. I'm looking at used outboards to start it off and work kinks out of. Are the 25hp Johnnyrudes good motors? I know they remained very similar for many years but I'd be looking into mid 80's white motors. How many years are basically interchangeable?

 

[flyingscott]

They are excellent motors. 85 or later would be my choice.

 

[matt167]

What changed in the engine?

 

[flyingscott]

Lower unit changed they went to a through hub exhaust which is a better design.

 

[BTL]

I have a 1988 25hp and I love it. I beat the hell out of it and the only problems I've had were my own fault.

 

[matt167]

cool. looks like these are engines to search out, and it's good because they aren't hard to find. Makes sense with the exhaust. I've listened to some of the older ones on Youtube and the exhaust sounds different than the later ones

 

[flyingscott]

cool. looks like these are engines to search out, and it's good because they aren't hard to find. Makes sense with the exhaust. I've listened to some of the older ones on Youtube and the exhaust sounds different than the later ones

Its not about the exhaust its about the gears they used which are better than the previous lower unit. And better bearing set ups.

 

[F_R]

The thru-hub design is faster too. It's just a better shape. Hydro-dynamic I guess is the word.

 

[matt167]

I know, from a design standpoint I understood why it would be better after comparing the 2, but the older ones are for sure louder as well.

I had even found a 28 SPL but after I found out they don't have thru hub exhaust. I discounted them

 

[hardwater fisherman]

Much better props on the newer design as well... And many different props to chose from with the thru-hub...And the older ones cost more..

 

[jimmbo]

Well the Non Thru Hub model does perform a bit better in reverse, but in forward the Thru Hub version is better. More advanced Prop Design regarding Blade Shape and Rake. The gears themselves are larger and stronger. We had a 1979 25hp and a 1980 35hp, on identical boats(14 ft car toppers) . Top speed difference was as expected, about 2 - 3 mph. The 25 idled quite a bit smoother than than the 35, but again that was expected.

 

[matt167]

How many years was that powerhead block used? I know it was 20,25,28 SPL, 30 and 35's before prop shaft rating

 

[racerone]

From 1976 to 2005 with minor changes / variations of course.

 

[Guest]

The 25hp Powerheads from 1976 and prior were 22 cu. in. twins, based on the old Johnson 18hp platform from the 1950's, these were solid and dependable mills, right up until they went out of profduction. In 1976, OMC introduced the larger 31.5 cubic inch twin, and marketed it at 35 hp. all 25's from 1977 onward to 2005 used this platform. its solid fast and easy to work on. I have a 1993 25 Evinrude, I put a 30hp carb on it, boysen 2 stage reeds and run a Ballistich prop on this Sea Nymph 14R. She runs along with motors more than twice her size.
These motors are great, but be careful, after owning one, that expensive (and heavy) 4 stroke Zuki might dissappoint...

 

[matt167]

This boat will spend a lot of time at idle- displacement speeds exploring the canals, where a 4 stroke would be better. It's a ~60 lbs difference but for sure if the Johnnyrude works good enough, theres no reason to upgrade

 

[matt167]

I'm picking up what I'm pretty sure is an '87ish Johnson 20hp fairly local. I don't have the exact model number but from the decals and similar motors + hub exhaust it's around that time. Complete with controls, the guy is de rigging his boat for a larger motor

 

[jimmbo]

I know the blocks, cylinder heads, carbs, were different on our 79 25 hp and our 80 35hp. They shared the same displacement, but not much else

 

[matt167]

As far as I've been able to figure out. 20 and 25hp were basically the same. The intake and carburator is different but some years they actually share the same carb.

The 30/35 is ported differently, with a different carb and a different exhaust housing. And then there is the 28 SPL which was a 30hp powerhead on the older style 25hp leg

For this boat/ motor. I'm going to keep it as a 20hp unless I find it needs a little more and then I'll gather the parts to switch it to a 25hp. I won't know if it has a 25hp carb on it until I know the actual model number

 

[Newyota]

As far as I've been able to figure out. 20 and 25hp were basically the same. The intake and carburator is different but some years they actually share the same carb.

The 30/35 is ported differently, with a different carb and a different exhaust housing. And then there is the 28 SPL which was a 30hp powerhead on the older style 25hp leg

For this boat/ motor. I'm going to keep it as a 20hp unless I find it needs a little more and then I'll gather the parts to switch it to a 25hp. I won't know if it has a 25hp carb on it until I know the actual model number

My 1985 20hp shares the same carb as the 25hp I discovered after buying package deal of intake and carb I swapped out the intake.I personally did not notice a difference though in any increase in speed anyway.I was wondering what the differenc ewas on the 28 special as far as the power head,now I know it has the 30hp head on it.The carb does have a bigger main in it though compared to the 25hp of the same era.I recently found the 1980 25hp though does have the same main jet as the 28hp.

 

[jimmbo]

Comparing jets is really a waste of time, The carbs themselves are different in respect to air flow capacity, which is why they have different jetting

In addition, putting a carb from a higher HP engine does not always yield more HP, let alone convert it from a 25 to a 35. Increased air going in, also has more exhaust to exit, thus differences on the exhaust side, especially when exhaust tuning is part of the deal