1989 20 HP Johnson power upgraded to 25 HP for zero dollars

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Stefan

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My outboard is a 20 HP Johnson, 1989, 2 Stroke, Model # CJ20CRCEM

I did some research and found out that the 20 HP models from that vintage carry the same powerhead and gear casing as the 25, 30 and 35 HP.

Difference between the 20 HP and 30 / 35 HP are larger intake manifold and carbs.

Difference between the 20 HP and 25 HP is the intake manifold isn't restricted on the 25 HP. In other words, the 20 HP is the exact same engine as the 25 HP, including the carb and intake manifold, it's just that the intake manifold is restricted on the 20 HP.

I double checked this on BRP's (Bombardier who took over Johnson / Evinrude) website. By using the parts diagrams for the different sized engines I was able to verify this.

By boring out the intake manifold on my 20 HP motor, to match exactly to the opening of the carb, I gained an extra 5 HP for no funds spent.

How did I do this?

First thing I did is carefully remove the intake manifold and carb, which is pretty easy to do. Just take your time. Next, I found a bottle cap that matched the opening of the carb exactly (a peroxide bottle cap with a diameter of 1.25 inches). I then seated the carb onto the intake manifold exactly how it would seat if mounted on the engine, by lining up the bolt holes, and then I sprayed some white lithium grease through the carb opening which provided for an outline over the restrictor plate.

This gave me a reference point with which to place the peroxide bottle cap on the exposed intake manifold with the carb removed, allowing me to outline with a pencil the exact area on the intake manifold that needed to be bored out in order to allow unrestriced airflow. Next, I used a very small file to carefully file away to the edge of the pencil mark, filing in even strokes. This was a slow process. To clean up the edges I used a dremel tool in order to smooth out the new opening. It is very important at this point to use compressed air, a rag, or whatever thorough method to remove from the intake manifold any steel shillings from filing to ensure that they do not enter the cylinders. This is also a great opportunity to clean up your intake manifold, paint it, and give your carb a good wipe down / cleaning. Finally, I reinstalled the parts.

Results:

Before - with the restricted intake manifold my boat was bogged down, did not plane and topped out around 25 km/h. Even worst with a passenger. I tried shifting weight around, reducing weight on the boat and many other makeshifts solution to get the boat to plane and cruise better.

After - with the intake manifold now unrestricted my boat planes with ease and cruises along at about 43 km / h. Planes with a passenger and cruises along just a tad slower with the added weight. Increased air flow made my engine easier to start and it now idles better too. Next will be to get a prop with a bigger pitch to squeeze even more speed, as the extra power will be able to turn a higher pitch. I could not be happier with the results, and the best part is it was done for zero dollars expended, only about 2 hours of my time. I get to my fishing destination faster, which means I save fuel because the engine isn't running as much and it is pushing a boat that is on plane rather than bogged down. I tested this for the first time this past week and I am still grining ear to ear.

Other Considerations - I had originally intended to upgrade my engine by purchasing a 30 hp carb and intake manifold, which would have cost at least $200 if I could find good, used parts. However, by discovering that the intake manifold could be bored open I did not have to go the route of purchasing new hardware, while still achieving the desired result. This mod gave me just the extra power I required. If you have a 20 HP motor of this vintage, why not do the mod, even if you don't need the extra power? If you do need the extra power, this mod might achieve the same result for you as it did for me depending on the size of your boat.

Hope this helped. Good luck, happy boating and fishing.
 

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Thank you , I couldn't be more happy in my fishing machine. A few small details to finish off, hopefully over the winter time.
 
I opened up my carb today and peeked inside...It looks just like this in a 1990 Evinrude 20 CRESB motor.

I've been planning on trying to find a 30 carb/intake but they aren't that common on e-bay.

I may just try this.

Do you have any pictures of actually removing the starter/carb? I can't see an easy way to get the carb off.
 
[url=https://www.tinboats.net/forum/viewtopic.php?p=327071#p327071 said:
Plasticmotif » 23 minutes ago[/url]"]I opened up my carb today and peeked inside...It looks just like this in a 1990 Evinrude 20 CRESB motor.

I've been planning on trying to find a 30 carb/intake but they aren't that common on e-bay.

I may just try this.

Do you have any pictures of actually removing the starter/carb? I can't see an easy way to get the carb off.


I don't have any pics of the removal process and I didn't have to remove a starter since my motor is not electric start... However, it was real easy to remove the carb.

There were three components that have to be removed.

1 The linkage arm (about 1 inch long) that is the go between from the throttle control to the carb regulating the butterfly inside the carb , simply pops off on both ends with steady, light pressure.

2 Two fuel lines, use a small flat head screw driver to pop them off with light pressure

3 Two nuts that secure the carb to the intake manifold. As you loossen the nuts lift the carb at the same time with your other hand so the nuts dont hurt the components that are directly above them.


The intake manifold is a piece of cake to remove. Just a couple of flat head bolts, the rest i believe were 3/8 inch rachet style bolts, about 5 of them.

If you're still having problems post some pics of your carb on this thread and we can go from there. Ask any questions you may have. If you end up doing this mod, please let me know how it worked out for you, I'm very interested.
 
Got my manifold off. Going to start the slow process of rounding out the keyhole!

Starting coarse then using a chainsaw sharpener to buff it out.
 
[url=https://www.tinboats.net/forum/viewtopic.php?p=327619#p327619 said:
Plasticmotif » 25 minutes ago[/url]"]Got my manifold off. Going to start the slow process of rounding out the keyhole!

Starting coarse then using a chainsaw sharpener to buff it out.


That's great! Looking forward to hearing about the results plus any suggestions you might be able to offer that would make this process easier.
 
Got it roughed in. It's not an exact perfect circle but it's lined up properly. I aligned the carb onto the manifold and stuck a pencil through the butterfly and marked the edges of the carb. I got a 10" rounded file and roughed it in. Polished a bit with a dremel. Now I'm polishing with fine sand paper. Will clean-up and try to install tomorrow!
 
That's great, the hardest part is over now... I'm sure you did a very good job.

When do you think you're doing to test it out? When you do bring a GPS with you so you can track your speed.

How is your prop looking? Mine had some burs on it and I used an angle grinder to debur it. Seemed to help quite a bit, will tide me over till I get a new one. The prop on my motor is a 10.5 x 11.. Thinking of trying a higher pitch, but still need to research this a bit more.
 
Mine's a 10x13.

I'd test it out soon.....but, my registration lapsed. I've not registered the boat to me as I've only had it a short time. So, I've got to pay taxes on it as well. Need to wait till next payday. Had to pay for my wife's last semester of graduate school and car insurance so I was skinned!

If I can get it registered Friday, I'll probably take it out this weekend. Provided I don't go dove hunting.

Speed doesn't matter much to me - as long as it planes out. I wasn't able to plane out with two people in the boat before.
 
I understand Mac, things are pretty tight, for pretty much everyone it seems... Thank goodness we have our boats to escape for a while...

I think this mod should help your boat to plane. I wonder if one of those Dol-Fins, might help as well. Ive heard mixed reviews on them, but ive heard instances of them working... I might just try it..
 
im a little confused here. you say the difference in the 20hp and 25hp is that the 25 intake is not restricted and the 20 intake is restricted. so in theory the only thing that gives the 25hp 5 more HP than the 20hp is more air into the intake manifold. so you would think that both the 20hp and 25hp have the same carbs but the 20hp intake restricts more air going into the engine hence 5 less HP. but the 20 and 25 have different carbs so I would think that even if both intakes were not restricted it wouldn't matter because the 25 has a bigger carb than the 20hp and would still be putting more air than the 20hp with the intakes being unrestricted so I don't see where the 5 extra hp is coming from with both motors having different carbs and intakes. from the late 70's into the 80's both the 25hp and the 35hp had the same powerheads, intakes and inner exhaust tubes. the difference in 10hp is that the 25hp carbs have a restricter inside the carb throat so to get 35hp out of the 25hp you put a 35 carb on the 25hp motor thats why I cant understand where you get 5 more hp without changing your carbs. granted im tired as hell and may be missing something but this thread got my attention because I have a 1980 25hp Johnson and I put the bigger 35 carb on mine for a 10hp gain and your theory about the intakes just don't add up to me. but like I said im nodding off and may be missing something so don't assume im saying your wrong im just saying that I don't get it... so if you can explain it better I really would like to know if im wrong.
 
this is driving me nuts thinking about it so I shot johnny25 a message and asked him to read this and see what he thinks. again if im wrong I apologize and am not saying you don't know what your talking about. im sure after some sleep and I can think straight i'll see that I may be mistaken....
 
Sounds to me like the the intake just restricts air flow Shawnfish. Like the plates they use in NASCAR limiting the HP. If you look at an engine as if it was an air pump, the smoother the flow of air through the intake and the more efficiently you can scavenge the exhaust ,the more HP you can make.
 
[url=https://www.tinboats.net/forum/viewtopic.php?p=327756#p327756 said:
shawnfish » Today, 06:15[/url]"]this is driving me nuts thinking about it so I shot johnny25 a message and asked him to read this and see what he thinks. again if im wrong I apologize and am not saying you don't know what your talking about. im sure after some sleep and I can think straight i'll see that I may be mistaken....


Hi Shawnfish,

Check out this link here to BRP for Johnson 1989, 20 HP and 25 HP models.

20 HP Carb is part # 0433193 (this is what is etched on the carb on my 20 HP as well)
25 HP Carb is part # 0432704

So the carbs are definitely different part #'s, but from all the research I have done the only difference between the two engines is that key hole restrictor plate on the intake manifold of the 20 HP...

Perhaps the carbs are exactly the same, but were just cataloged in their inventory differently as seperate part #'s for sorting purposes??? Or perhaps they just assign the 25 HP a different part #, so it seems like it is a different part and they can charge more $$$ for it? Or maybe I am completely wrong, you could be right and they are different carbs all together?

Either way, the results speak for themselves: when I bored out that key hole on the intake to match the carb perfectly, air flow increased, speed increased, the boat planed, the engine idles better and I'm still smiling. More air resulted in more power...
 
[url=https://www.tinboats.net/forum/viewtopic.php?p=327765#p327765 said:
Stefan » Today, 07:23[/url]"]
[url=https://www.tinboats.net/forum/viewtopic.php?p=327756#p327756 said:
shawnfish » Today, 06:15[/url]"]this is driving me nuts thinking about it so I shot johnny25 a message and asked him to read this and see what he thinks. again if im wrong I apologize and am not saying you don't know what your talking about. im sure after some sleep and I can think straight i'll see that I may be mistaken....


Hi Shawnfish,

Check out this link here to BRP for Johnson 1989, 20 HP and 25 HP models.

20 HP Carb is part # 0433193 (this is what is etched on the carb on my 20 HP as well)
25 HP Carb is part # 0432704

So the carbs are definitely different part #'s, but from all the research I have done the only difference between the two engines is that key hole restrictor plate on the intake manifold of the 20 HP...

Perhaps the carbs are exactly the same, but were just cataloged in their inventory differently as seperate part #'s for sorting purposes??? Or perhaps they just assign the 25 HP a different part #, so it seems like it is a different part and they can charge more $$$ for it? Or maybe I am completely wrong, you could be right and they are different carbs all together?

Either way, the results speak for themselves: when I bored out that key hole on the intake to match the carb perfectly, air flow increased, speed increased, the boat planed, the engine idles better and I'm still smiling. More air resulted in more power...


I checked 2 other sites along with BPR before I posted to be sure. and if the carbs are the same but have different numbers for the 20's and 25's then you would think the intakes would be assigned different numbers?????? to me it just seems logical that the 25 is capable of pushing more air than the 20 because why else wouldn't both motors have the same carbs with the difference being the restrictor on the intake on the 20hp? I guess im torturing myself thinking about it because if you say you got more hp from doing it then that's all that really matters I just dont get it lol! that's weird your casting numbers show up as the actual part number for your carb because I know up until at least 1984 if you run any casting number in a parts search 98% of the time it comes up as there is no match for that number and I do know that some parts from back then had the same cast numbers on them but the parts would be used on different years and hp's motors.... and to charger that's exactly how I was thinking in regards to the restrictor plate races for nascar......
 
Ok I skimmed the thread real quick as I am in a hurry today but will try and give my 2 cents. Yes the only difference in 20 and 25hp in this year is the restricted intake design. The 20 and 25hp starting in 1985 had identical carburetors. I believe I covered this in my 20/25hp to 30hp conversion thread but maybe I didn't? We could debate all day whether it actually gives an extra 5hp by boring the intake out but unless someone has a dyno for outboards we may never know. the theory is there though.....more air in should make more HP. I will also say that I owned an 85' 20hp and it did not seem to run as smooth as my 85' 30hp or my 88' 25hp and this I suspect was because of the restricted intake. The motor really seemed to want more air.

Now a little history on the 20hp.......the 20hp motors that we are talking about came out in 1985. The same year OMC started prop rating the HP of there motors. Before that the 20hp was last made in 73' in the smaller 22ci block, and only the johnson logo or tag was released in the 20hp. Evinrude never had the 20hp tag until 1985....they were labeled 18hp pre 74' I believe although I suspect motors were identical. Likely a marketing ploy of some sort. Also in 1984 the 35hp was discontinued and became the 30hp of 1985. The 35 was brought back for one year in 1987 but it was a restricted 40/50 HP motor. And then again somewhere in the 90's I believe it came back but now I am at the limits of my memory without researching again.

But in short......in 1985 the 20hp came out and had a restricted intake, and only that is what separated it from the 25 for several years. I'm not sure but I believe at some point there was more than just the intake difference in the 20 and 25 but cannot remember when it was? In the 90's I believe
 
[url=https://www.tinboats.net/forum/viewtopic.php?p=327778#p327778 said:
Johny25 » 42 minutes ago[/url]"]Ok I skimmed the thread real quick as I am in a hurry today but will try and give my 2 cents. Yes the only difference in 20 and 25hp in this year is the restricted intake design. The 20 and 25hp starting in 1985 had identical carburetors. I believe I covered this in my 20/25hp to 30hp conversion thread but maybe I didn't? We could debate all day whether it actually gives an extra 5hp by boring the intake out but unless someone has a dyno for outboards we may never know. the theory is there though.....more air in should make more HP. I will also say that I owned an 85' 20hp and it did not seem to run as smooth as my 85' 30hp or my 88' 25hp and this I suspect was because of the restricted intake. The motor really seemed to want more air.

Now a little history on the 20hp.......the 20hp motors that we are talking about came out in 1985. The same year OMC started prop rating the HP of there motors. Before that the 20hp was last made in 73' in the smaller 22ci block, and only the johnson logo or tag was released in the 20hp. Evinrude never had the 20hp tag until 1985....they were labeled 18hp pre 74' I believe although I suspect motors were identical. Likely a marketing ploy of some sort. Also in 1984 the 35hp was discontinued and became the 30hp of 1985. The 35 was brought back for one year in 1987 but it was a restricted 40/50 HP motor. And then again somewhere in the 90's I believe it came back but now I am at the limits of my memory without researching again.

But in short......in 1985 the 20hp came out and had a restricted intake, and only that is what separated it from the 25 for several years. I'm not sure but I believe at some point there was more than just the intake difference in the 20 and 25 but cannot remember when it was? In the 90's I believe


ok so starting in 85 the 20 and 25 had identical carburetors but for some reason or another they used different part numbers on the carbs and its the restricted intake on the 20 that makes the difference and not carb size.. hmmmmm....... well that makes sense to me, logical sense? no. but I understand now why my 1980 25 carb is the same exact size as the 35 carb and both have different numbers with the only difference being the 25 has a plastic ring inside the throat narrowing it to restrict the air flow a bit and to make the same powerhead as the 35 only produce 25hp. well Stefan sorry I drug this out and johnny25 into it to help me understand how and why but my hats off to ya for using your melon and getting 5 more HP out of your motor without spending a dime or whatever you use up there for coin. and thanks a lot johnny25 for going out of your way once again and helping a fella out!!!!
 

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