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

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

Here is the 25hp intake measurement at 5 and 1/8 inches
http://i279.photobucket.com/albums/kk160/Timtoboyko/DSCN6371.jpg

This is the 35hp hole that the carb mounts to. Right at 1 and 1/2 inches
http://i279.photobucket.com/albums/kk160/Timtoboyko/DSCN6373.jpg

And the 25hp hole intake hole is 1 and 3/8 inches, maybe a fuzz bigger.
http://i279.photobucket.com/albums/kk160/Timtoboyko/DSCN6375.jpg

This is a view of the inside of the 25hp intake and carb attached.
http://i279.photobucket.com/albums/kk160/Timtoboyko/DSCN6377.jpg

And this is the inside looking out of the 35hp intake and carb.
http://i279.photobucket.com/albums/kk160/Timtoboyko/DSCN6379.jpg

And the 35hp intake is actually an 1/8 of an inch deeper/taller than the 25hp intake. And what I mean by that is if you measure from the reed plate out it is an 1/8 in taller when installed.

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

And the last thing I noticed was the nipple for the primer on the 35hp intake was much larger than the 25hp.

The 35hp nipple
http://i279.photobucket.com/albums/kk160/Timtoboyko/DSCN6381.jpg

The 25hp nipple, which is so small you can barely see it.
http://i279.photobucket.com/albums/kk160/Timtoboyko/DSCN6382.jpg

Now you can bore out the carb and intake as I originally planned but it is going to be very time consuming to do the intake right. And I don't know how you would ever get the inside to spec, especially considering that the 35hp intake is deeper/taller. So I don't see how you could get the volume of the 35 by boring the 25 out? The hole would be easy to bore but the volume of air the 35hp intake can hold and move is much greater on the inside. So for $70 bucks I got the carb, intake and reed plate off of ebay. Had to look around a little but got lucky and found a guy 30 miles from me parting out a 35hp military johnson and didn't have to pay shipping off of ebay

I may post more if people ask.
UPDATE: Ok here is a few pics of the see threw chainsaw/lawnmower fuel line I purchased to go over the larger nipple on the larger intake. This fuel line is much easier to get over the nipple due to its flexibility I believe it is 1/4" line and I zip tied it with small 4" ties. It will be a snug fit over the primer nipple but it will go on.

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

if you need more stuff for the 25/35 jonny/rudes pls pm me, I will give it to you (you pay shipping) I have so many of these most are junkers & I often throw complete powerheads in the dump. I currently have 24, they are all salt run engines.

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

Ok update: I finished the modification tonight and the motor runs AWESOME! Idles way better than it did with the 25 carb and intake. Not to mention the throttle response is much better. Had to adjust the pivot pin on the throttle cable/rod to compensate for the motor wanting the carburetor opened quicker. I only got to run it in a barrel tonight but plan to be on the lake soon after I go get my boat out of storage. But I can easily tell the difference already. Idles like a champ now! And the power and response is much crisper without a doubt. I am starting to think these motors are meant to have more fuel and air and run much better as so. I will have more updates and possibly a video when I get her out on the lake.

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

Wow, you work fast! Look forward to seeing the video.

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

I can probably take these johnsons apart and put them together with my eyes closed. Hello jasper, I was born and raised in MN. I wish there were as many motors out here as back there. On a good year you will see maybe 20 johnson outboards on craigslist all year. They are like gold out here and worth a lot more also. A $500 dollar motor in MN is worth $800 to $1000 here easy. I miss all the lakes, boats, and motors over there

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

Johny25,
I'm fairly new the Minnesota. I bought my very first boat/motor a few years ago. I found this site and learned some basic motor maintenance and repair. There's a lake near my home that I usually fish, but I plan to get out and explore more lakes this year.

$70 for the hp upgrade is pretty darn cheap. Thanks for documenting and sharing the details. This dispels the myth of a carb swap is all it takes. Good job!

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

Interesting, For kicks i went and measured my `81 evinrude 35 hp carb/ intake. Carb has the larger venturi but has the smaller 1 3/8'' intake opening. Intake manifold on my motor is correct according to parts breakdown- # 386792. So, i went and looked at different yr Part #`s and it looks like up to `83 they use #386792 on the 35 hp`s, `84 up #395626 is used. Must be the larger opening/ volumne intake. Would you post your manifold part #`s for comparison?
I guess if anyone is going to try this you should make sure you are getting the intake manifold for the `84 on up 35 hp. Also check on the 30 hp intake to which they were using.

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

My 1988 25hp came with intake part #396788 and the 1984 35hp intake I put on was part #396790. I do know that the 30hp of 1984 had the same intake as my 1988 25hp. But you have to remember that in 85 the 35hp basically became a 30hp due to prop HP rating and not the flywheel HP rating as before. I know in 88 they did not make a 35hp even though some sites show parts for an 88 35hp. I have never seen one and do not think they exist. Basically if I understand it correct, in 85 when they went to prop HP rating the 30hp motors from then on were the same as the pre 1985 35hp motors. So in reality I made my 25 into a 30, and not into a 35hp. I put 35hp parts on it but they are pre 85 35hp parts which makes it a 30 in prop HP reality.

Your part number you listed on tour 83' intake is the same as the 84' 30hp intake and the same as my 88 25hp intake. There are a few different part numbers for the same intake and yours is the same as my 88 25hp. My guess is that you could put the larger 35hp intake of the 84s and up and get a couple more ponies out of it because it is a larger intake. The 35hp intakes from 84 and up had a couple part numbers also #396790, #395626 and #391054. That is probably due to the different primer and choke models?

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

And you are correct about getting the intake also and just not the 35hp carb. Just enlarging the hole will not get you the full benefit of the 35hp carburetor either. As I mentioned above, the intake on the 35hp has a larger volume inside and it also comes off the reed plate an extra 1/8 of an inch. Meaning if you stick a tape measure through the intake hole and touch the reed plate it is taller by 1/8 inch than the 25hp intake. So even porting or boring the 25hp intake on the inside will not give the 35hp carb enough are flow. The intake mold is just to small as I see it.

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

Johny25,
all you need now are some new stickers. What kind of boat you gonna mount it on?
Here's a video of mine in action...
http://www.youtube.com/watch?v=wd5TOTrxFSs

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

Wow that is you! I have watched that video at least 10 times and it was you all along lol, small world eh. I'm not going to put 30hp stickers on it because my boat is only rated for a 25

I am putting it on my 2001 Lowe 1467t and it is going to replace my 1987 9.9hp that I converted to a 15hp last year. But with all the custom flooring and seats I put in the 15hp only pushed it at about 15mph. I added about 150-175 lbs of weight with all the custom work I did so I needed a 25-30hp. But it took me a year of looking around here to find one I wanted, but I got it
http://i279.photobucket.com/albums/kk160/Timtoboyko/DSCN5619.jpg

The camo seat is for my 3yr old son, the middle seat if for my wife when she goes out with us. Both of those seats are removable and can be removed in about 30 seconds. The seat up front is for my fishing buddy, my 6yr old son He always goes out with me, and this year my 3yr old will spend more time out there with us.http://i279.photobucket.com/albums/kk160/Timtoboyko/DSCN5626.jpg

This was the before pic of the boat, I had to pull one off the internet because I didn't take a pic before I started my work. And yeah I cut the middle bench seat in half lol

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

Since I could not buy a infant boat seat I customized a camo seat I had already for my 2yr old. I put side guards and handle grips to keep him from falling to the side when turning and a crotch guard to keep him from sliding out the front of the seat. As you know you cannot seat belt children in a boat (nobody for that matter lol). I have had so many people on the lake ask me where I bought this and when I tell them I built it myself they ask what I would charge to make them one.

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

I have a 1990 20 that I'd love to do this to. I've been researching for a while. It seems as though the part numbers for carbs, intakes, and rotating assemblys are the same for the 20, 25, and 30hp engines of the same year.

Idea's?

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

The child seat is very clever in deed. You can't start them too young. I wish I would taken my kids more when they were younger. I have a 21 yr old son and 14 yr old daughter, and neither have much interest in fishing. Oh well. I think the wife felt sorry for me, and went once last season. Of course, I had to wait until after noon to go.

Anywho, that's a fantastic mod. I like the whole boat pkg. Are you a member of tinboats? Thanks for sharing.

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

tacoma_2002 said:

I have a 1990 20 that I'd love to do this to. I've been researching for a while. It seems as though the part numbers for carbs, intakes, and rotating assemblys are the same for the 20, 25, and 30hp engines of the same year.

Idea's?

Click to expand...

I am about 99% sure you can do the exact mod that I did tacoma and make it into a 30/35. Carb and intake is all you need

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

jasper60103 said:

The child seat is very clever in deed. You can't start them too young. I wish I would taken my kids more when they were younger. I have a 21 yr old son and 14 yr old daughter, and neither have much interest in fishing. Oh well. I think the wife felt sorry for me, and went once last season. Of course, I had to wait until after noon to go.

Anywho, that's a fantastic mod. I like the whole boat pkg. Are you a member of tinboats? Thanks for sharing.

Click to expand...

Thank you jasper, and no I'm not a member of tinboats. I don't even know what tinboats is lol. And I totally understand the wife thing. I come back to the landing to pick her up at 1-2pm usually because I am on the lake before sunrise.

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

dang, Johny, before I saw that other seat I thought the 2 year old was driving this rig

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

Trust me, all I hear when he is in the boat is "me drive dad?" lol, he is fascinated with motors. I have let him steer my 15hp before and he had an absolute blast. I had to pry his hand off the throttle My 6yr old could care less about motors though