Page 12 of 12

1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics

Posted: 24 Oct 2015, 07:57
by alfaguy
Does anyone change the plastic timing cam when making the 25 to 30 conversion. Another post indicated they are different, even though the parts breakdowns show the same number for both models. I ordered the part quoted and they are indeed different, and it seems the 30 hp cam does not advance as quickly as the 25. I will look for the part number if anyone is interested.

1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics

Posted: 26 Oct 2015, 03:30
by thill
Edstrossner,
I've read your posts with interest, as far as opening up the throats to give the motor more lung capacity, and as far as shaving heads, to increase compression.

But what did you do as far as getting more fuel mixture into the increased airflow? Perhaps, it's as simple as going up a main jet size or two?

DUHHH... Just noticed where you went to a 63D main jet. I had only read the earlier post, and not that last report.

-TH

1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics

Posted: 12 Apr 2016, 17:30
by bamalivin
I have a 1989 Evenrude tracker 20 hp that I am prepping for this upgrade. I know that yours is a 1988 but are the same parts compatible. I have read conflicting information regrading this part interchangeability. I read the thread and understand that I will also potentially be in need of a intake, I just want to make dang sure before I start ordering parts. I did notice a color scheme difference between your 1988 and my 1989. Mine is just like the one in the video that I am linking to this post (except mine is a 20 hp of course). I appreciate any help and advise that can be passed in advance. ~Billy

https://www.youtube.com/watch?v=xmckQll ... tml5=False

1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics

Posted: 08 Jan 2019, 17:20
by the-outdoorsman
I was led to this thread by way of google so this is my first post. I am not sure if anyone is following it anymore but I hope so. I have a 1990 Evinrude 20 hp (E20CRESB). From reading through a lot of these posts it seems I should be able to do this conversion. I know I can bore out the hole in the intake to make it a 25hp but I want to convert it to the 30hp. How do I go about figuring out the part numbers for the intake and the carb? I think that is the only two things I need to buy. When I look up a 1990 30 hp, there are several model numbers.

Any help would be much appreciated.

1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics

Posted: 12 Jan 2019, 05:13
by nccatfisher
Well if you googled the original question I would have thought you would have tried a search here for your second one, you would have found it has been asked numerous times with usually the same success. You will most likely have to just dig around to you find them quite honestly. There are a couple old threads here with various numbers that will work depending on model.

1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics

Posted: 14 Jan 2019, 15:08
by wmk0002
Interesting that this thread got bumped as I was just looking at it last week. Guy locally is selling a set of a 35hp carb and intake for $50 and has two sets. I was thinking about buying both so I could try this out if I ever get the correct model motor to try it on. Then maybe selling the other one on here. Anyone know what the going rate of the carb and intake manifold would be?

1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics

Posted: 15 Jan 2019, 18:00
by the-outdoorsman
nccatfisher wrote:Well if you googled the original question I would have thought you would have tried a search here for your second one, you would have found it has been asked numerous times with usually the same success. You will most likely have to just dig around to you find them quite honestly. There are a couple old threads here with various numbers that will work depending on model.
Well I did a search before I posted here and again after and I have not found any carb numbers or a thread that would tell me how to figure it out. I am sure it is how I am searching for it with my key words. I did find a member that did his 1990 motor and sent him a PM but his post is from 2014 so probably a long shot.

1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics

Posted: 26 Feb 2019, 15:15
by durco
Johny25 wrote:Well lucesco I know some of those years you are talking about had different gear cases which could cause a problem when putting 10 to 15 more HP to them. You would have to cross reference to see what the differences are for what year motor you are talking about. I know I was talking to someone with an 80' or 81' and the 20hp of that year has the smaller split gear case than the 35hp. Would hate to see people doing this mod and ripping their gear cases apart so look into it. Or ask and maybe I or another can help you.
1984 was the last year of split gear case on 20-25.

1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics

Posted: 26 Feb 2019, 15:24
by durco
Johny25 wrote:I did a quick cross reference and the intakes are the same. Different carburetor and the cylinder and crankcase assembly has different part numbers #-o I couldn't really tell what the difference was other than the starter bracket but there must be something else I believe. This will be a big road block in doing this conversion if the crankcase is different on the 30 than the 25. But it was just a quick look at them.

This shows the 25 and the 30hp crankcases and the different part numbers.
http://www.marineengine.com/parts/johns ... +Crankcase
The 9.9 to 15 is the only true swap with just the carburetor change. On the 25-30-35 there is a crankcase change, to wit: the 20, 25 and some 30's have "finger" ports on the chamber intake ports. 35's have "bridge" ports. True 35's will have maybe a little rougher idle and a rougher transition (from low rpm carb circuit to high carb circuit) than a jacked up 20, 25 or 30. Not saying you won't gain from the intake and carb swap; you just won't quite get the full "monty" with it.

1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics

Posted: 26 Feb 2019, 15:33
by durco
Johny25 wrote:
Jay D wrote:I have a 1988 25hp evinrude, what would it take to boost it to a 35hp evenrude? If you already answered this please forgive me.
I made this whole thread from the exact year and HP motor you have Jay. Start at the beginning of the thread where I layout and have pics of your exact motor converting into a 30hp. It will never be a 35hp since the 35 was re-badged to a 30hp in 1985 when OMC prop rated the HP on there motors. The old 35's were only cranking out 30hp at the prop hence the reason it was labeled the 30hp after 1984. Read the first page of the thread and let me know if you have any questions :)
I have a 1984 35 and a 1988 30. You can really feel the difference between the two; the 35 being stronger. When I change motors on the same hull I have to move the tilt pin because the 35 will porpoise whereas the 30 will not. Same pitch prop (13). Did some research in the parts manual. 1984 35 has a different crankcase than a 1985 30. So, when I went to OMC service school in 2000, I asked my instructor what the difference was. He said, "finger ports" vs. "bridge ports". Bridge ports make the true "hot-rod" 35.

1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics

Posted: 26 Feb 2019, 15:41
by durco
Natemeins wrote:After doing a fair amount of part number cross referencing, it appears the 30 and 35 hp motors in 1984 used identical intakes, reeds, carbs, low speed needles, and high speed orifices. Even identical pistons, rods, and cranks. So how did they manage to get another 5 hp from one to the other?
By the difference in the shape of the transfer ports in the block. 30 and 35 have different blocks (machining)

1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics

Posted: 26 Feb 2019, 15:46
by durco
Johny25 wrote:1984 they did not make a 30hp......was a 35hp.
Yes, they did. It was the first year of the 30hp. However, they also made the 35 - it was the last year for the 35 in the U.S. (except for military and the later 3-cyl, etc.).

Re: 1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics

Posted: 10 Jun 2019, 22:43
by 1648grizz
Great thread, I bought a new 25hp 2 stroke Johnson in 2005. I believe this was the last year for the 25hp 2 stroke . On my 1648 Grizzly I would top out at 29 - 30 mph with the 10x13 prop that came with the motor. That was only me in the boat at 225lbs, I think the boat is around 400lbs.
Been looking into the carb swap and it looks like all I need is the 30hp carb off the 2005 30hp , same intake manifold .

Re: 1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics

Posted: 10 Jun 2019, 23:07
by 1648grizz
Johny25 wrote:
22 Feb 2012, 18:21
Another thing I forgot to mention was that when I had the 25hp intake on the motor and I took a flashlight and looked through the intake hole with the carburetor off I could see that the intake actually blocked part of the reed plate. This made it more difficult for the reeds to actually open up in my opinion, and caused air flow restrictions.

Yeah Bigwave if you decide to do the mod let me know your make and model and I would be happy to help cross reference to make sure you can do the mod with your year Johnson. I am not entirely sure you can do it to newer Johnsons but it would be interesting to find out if you could :)
Great thread Johny25, it looks like the only differences between my 2005 J25TESOM and the 2005 J30RSOD is the carb, same intake manifold .