80's johnson/evinrude 25hp to 30-35hp conversion with pics

[torbjorn]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

Ok I know this thread has been rehashed several times but I decided to put pics of the modification up and point out the differences between the 25hp and 35hp. Although the 35 became the 30 after the prop HP rating in 85'.

First is the carburetor difference: The 25hp is a 1988 and the 35hp is a 1984 carburetor.
(35HP on left 25HP on right) the throat of the 35 is much larger. Something like 9/16 inch larger in diameter. This is a front view.
http://i279.photobucket.com/albums/kk160/Timtoboyko/DSCN6363.jpg

(again 35hp on left and 25 on right) This is a pic of the backside of the carbs that bolt up to the intake manifold. Once again you can see the difference in the diameter of the hole between the two. The jets in the carb are bigger on the 35hp also and I may post pics of that when I rebuild the 35hp carb soon.
http://i279.photobucket.com/albums/kk160/Timtoboyko/DSCN6365.jpg

And 2nd is the intake manifold: Once again and 88' 25hp intake and a 84' 35hp intake.
First pic has the 25hp intake on the left and 35hp intake on the right, the 35 is wider and deeper than the 25. This allows for the increased air flow. The 25hp intake actually covers a small part of the reed plate when mounted. The larger circular ports on the 35 do not do this.
http://i279.photobucket.com/albums/kk160/Timtoboyko/DSCN6366.jpg

This pic has the 35hp intake in the front and 25hp intake in the back to show the difference in displacement. You can see on the 25hp intake that has the gasket line on it still. That line is how much larger the 35hp intake is. A good reference to the difference in volume.
http://i279.photobucket.com/albums/kk160/Timtoboyko/DSCN6369.jpg

Here is a measurement of the 35hp intake at 5 and 5/16 inch wide
http://i279.photobucket.com/albums/kk160/Timtoboyko/DSCN6370.jpg

Have to make 2nd post because I cant load anymore pics on this........continued below

The later model 30 carburetors have bigger jets because the venturi is bigger, 63D-67D. The GT-Pro
Class racers find the 62D to be the best but 63D should be ok if a bit slower. Do not change the 59D jet in the 1983 and older carbs, that jet size optimal for that model carburetor. You'll get 35 hp regardless of which year model 35 carb you use. I would stick with the older model metal carbs and avoid the newer ones with a plastic top. It's true that you'll have to pull the intake manifold and file out the opening to use the later model carb with primer. Acceleration may be better with the smaller venturi, I haven't tested it but met a similar case when racing the 3 cyl. 75 decades ago.

 

[Johny25]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

Hmm that is great info torbjorn. I wonder what size jet is in the 84' carb I put on mine? I will have to find that out next time I take the carb off.

 

[outkast7222]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

Anyone care to speculate what size intake this is for?

 

[Johny25]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

So your saying you have no idea what it came off of?

If I was to take a wild guess I would say it came off a commercial model motor of some kind. Looks like a restricted intake design to improve longevity of the engine. That is my speculation......

 

[outkast7222]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

No I know what it came off of, it is off of my E35ELCND. That is what confused me, seems the opening should be quite a bit bigger for a 35HP. This would be the second motor that someone mentioned having seen this on, the other was also a 1982 model. I have now opened it up and will see if it makes a real world difference.

 

[Johny25]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

Huh thats odd. It looks like a restricted intake. Do you know if it is the original intake that came with the motor? Or can you get a part number off of it? Looks like a 20-25hp intake design

 

[outkast7222]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

Huh thats odd. It looks like a restricted intake. Do you know if it is the original intake that came with the motor? Or can you get a part number off of it? Looks like a 20-25hp intake design

I do believe it is the original as the paint matched exactly and was not broken until I had it apart to replace the reeds. I did jot the part number down when I had it apart it is 390655. The 20-25hp design would make sense for as doggy of a motor it has been for me. I bought it from the original owner and he stated that he always had to run a 11 pitch prop on it when the factory recommended prop was a 13.

 

[Johny25]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

Yep that part number comes up as a 25hp intake. That model is obsolete but the replacement numbers match the later 80's 20 and 25hp intakes. Bore it out and I am sure you will get another 5 horsepower. It does not match the 35hp intakes of 82' so maybe it was replaced at sometime?

 

[outkast7222]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

Five minutes with a reamer and about 30 seconds with the Dremel. Hopefully get it out tomorrow to see if there is a difference.

 

[Johny25]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

What does your carb look like? Are you sure it is the larger venturi? You may have a 25hp carb on it also? Nice job reaming, looks factory

 

[outkast7222]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

When I cross the numbers from the carb it does come back as the 35hp carb so I believe it has the larger venturi of course all the pics I snapped are with the choke closed so I cant tell.

I did get it out on the lake and I will say it made a huge difference in hole shot and getting up to speed there is enough difference in RPM that I think I could safely jump up to a 13" pitch (that should get me back down to my RPM range). Previously it would run flat out at 22mph now it runs 30mph. Definitely worth it if there is anyone one else with little hole on their 35hp.

 

[Johny25]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

Yeah I can turn a 14 pitch stainless at 5650-5700 RPM on my 14ft boat at a 900lb total load. So depending on what size boat and weight you are pushing you may be able to turn a higher pitch than a 13? I have another thread on this forum with all sorts of prop info for your motor, you may want to check it out? http://forums.iboats.com/showthread.php?t=539571

 

[Jeepersheart]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

Ok I am very new to the whole boating world so bear with me here if this is a stupid question. I have an 83 25hp johnson model # J25RLCTE what you are saying is that I can basically turn it into a 30/35hp (depending on where the hp is measured) by swapping the carb and intake with those from a 35hp motor? It runs like a champ as is, pushed my 14' open glass steury with over 500lbs total load to a top speed of 26mph, but if I can squeeze a little more power out of her I might look into it.

 

[Johny25]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

Yes that is exactly what this thread is saying . You have an 83' so it probably has the split gear case. Not ideal really, because the 35hp in 83 had the larger one piece gearcase. Others have still done the mod and say the split gearcase can handle it no problem. But I do not know first hand on that.

What you really have in 83' is a 22-23hp maybe. This is because HP was rated at the flywheel and not the prop. In 85 they began rating at the prop. So technically by putting a 35hp carb and intake on your motor you will end up with a 30hp motor. Which is still a great increase in HP. The biggest difference I notice is the ability to go 27-28mph with 1100-1200 pounds total weight. That 5-10 extra HP really make a difference. Make sure you go up in pitch on your prop if you do this mod though or you will over rev your engine.

 

[weekendfisher]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

Would the 84 model carb and riser work with a 94 model 25 HP or did they change the parts in there at some point ?
I am considering doing this to my brother in laws boat as he has 25 HP pushing a 14 foot runabout it goes ok but a bit more power would be nice.
Thanks

 

[Johny25]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

Well I am not sure an 84' would work on a 94'? The 94 had the flat top carb. It probably would work but I am not positive. I would try and find a flat top carb closer to the year of your motor probably.

 

[Cab1040]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

i have a 1994 evinrude 25hp and am trying to do the intake and carb swap i have a 1979 35hp carb and intake will this years parts work they look like they will but the linkage on the carb appears to be different. from what im gathering on this thread i may need 1980's parts the 1979 intake will work because i have mocd it up. but the carb is my issue

 

[Johny25]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

And the thread lives on..... I believe the 79' carb had extra linkage for a choke butterfly. So I don't think that would work for you. I would think an 84' 35hp carb and all the 30hp carbs from 85' on would work but I will not put my name on it. I am just not as familiar with the 90's models. In 89' I believe they went to the style with the slow speed idle screw on the top/side of the carb. That may be the style you want?

 

[Cab1040]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

yes i have the screw on top of my carb now i think the problem im up against is my 1994 has a different choke assembly "style" then the old school manual choke. my carb now does not have a typical butterfly style choke. it seems to be some kinda primer type design.. if thats the difference the 1978 intake mani seems like it will work and i know the chamber of the 35 intake VS the 25hp intake is greater. so that might help. it will be 0 $ from my pocket to switch manis so no harm done all i can do is try and see how it does nothing but a lil time and test and tune with a lil satisfaction.NEVER KNOW UNLESS YOU TRY

 

[Johny25]

Re: 80's johnson/evinrude 25hp to 30-35hp conversion with pics

Ok in 78' they were still using the smaller intake style on the 35's and it is basically the same volume intake as the post 83' 25hp have. 1984 35hp was the first year of the larger intake volume. And then all the 30hp's after had the larger intake also.

Check your intake part number. You want 0391054, 0395626 or 0396790. If you have a 0386792, 0395698 or 0396788 then it is the smaller intake style.