1986 Johnson 20hp with 25hp carb filing plug

[Dano3578]

Ok, I bought a 1986 Johnson 20hp. Completely changed out all the fuel lines, pump and etc. Pulled down carb and noticed the main jet was crushed from previous owner. Couldn't find a 20hp carb to put back on so I was forced to put a 25hp carb. After doing exstinsive research and asking a few motorheads in my area, this conversion should be pretty simple. Keep in mind I DID NOT port the intake, just carb swop. Fresh spark plugs in, I take her to the lake and she fires up no problem and idles great. I take off and she flys across the lake !! I slow down and idle to make sure everything still looks and sounds good. I go to take off again and she doesn't quite plane off and is bogging down. I get back to the landing and pull the plugs to find them wet and black. I'm being told my plugs aren't firing enough to burn off fuel being dumped by the 25hp carb. I looked into getting hotter burning plugs , such as NGK instead of Champion. Im just thinking it's something more such as stator , power pack or coils. I haven't ran any other test yet to rule out any of the above Any feed back would be greatly appreciated.
P.S......Used in fresh water only since originally purchased

 

[ondarvr]

You don't put hotter plugs in to compensate for rich jetting, you re-jet the carb.

First check the parts diagram to see exactly what carb you have, the differences between it and the stock carb, and then start changing the jetting to get it closer, and that's only if the carb you put on is in good shape.

 

[Dano3578]

Thanks for the clarification on the hotter plug theory. I didn't think that would fix my problem. That was also a suggestion from someone
25hp carb came off of a mid 80's
It has the butterfly choke system
Really good shape

If it were jetting, couldn't I pull jets off old 20hp carb and put into 25carb? With the exception of the main pick up jet that was crushed with pliers

 

[Dano3578]

Forgive me man, I'm new to outboards but fairly well rounded in mechanics. I'm also $900 into boat motor and trailer. Trying to avoid bringing it to someone

I'll have to get numbers off carb or motor to match up. I work graveyard so that won't be possible right this minute

 

[Dano3578]

Also, by pulling intake off and boring to size to fit throat hole on the 25hp carb, will this help from filing out plugs?

 

[bowfisher2636]

Also, by pulling intake off and boring to size to fit throat hole on the 25hp carb, will this help from filing out plugs?

The extra fuel isn't causing your problem I just converted my 1988 evinrude 20hp to a 35 I did carb swap & carb intake swap I also have a new set of coils due to my oem ones failing earlier this summer before the conversion. Your problem sounds more of a fuel/air mixture taking a shot in the dark at it? Check the top adjustment screw when I replaced my carb I ran the adjuster all the way up and backed it off a turn and a half from there I think all in all I was exactly two turns backed out. Just be sure not to run it lean you will burn it up very quickly. I'm taking a wild guess at this but it sounds like you have more air in than fuel the adjustment knob has a o-ring that makes it stay in place inside there your o-ring may be delapatated therefor causing the knob to back out and allow more fuel. I would throughly inspect it

 

[bowfisher2636]

Also does your motor have the primer system on the left hand side of the motor

 

[Dano3578]

Thanks for your response Bowfisher,
I did read your post along with hundreds of others similar to mine. Brand new seal for mixture jet on the front the carb. I think you might have solved half if not my whole problem. I currently have that jet unscrewed 3-1/2 to 4 rounds open. I'll be fooling with it this week. I'll make sure to only open 1-1/2 to 2.

It did have manual primer system but I by passed it.
Also what you're saying is disregard the 100:1 fuel mixture sticker on the side of the motor and mix my fuel 50:1?

 

[Dano3578]

Now that I'm thinking about , the buddy I have helping me with motor gapped spark plugs at .04 because the old plugs I pulled off were at .04. I'm thinking they were just burnt up reading a .04 gap.....factory states .030 and plugs come pre gapped at .03. I'm purchasing 2 new NGK plugs tomorrow and will mix fresh non ethanol gas at 50:1, and set mixture screw at 1-1/2 out

 

[racerone]

Does spark jump a gap of 3/8" or more?---Note , the sparkplugs are not used to do this test.----What are the compression values.---Is the thermostat in place and working properly ?

 

[bowfisher2636]

Dano,
My plugs aren't gap setable the electrode is flush with the base it may have the wrong plugs in it when I purchased it. But may I ask why you have removed the primer system? All I had to was swap the screws on the bottom of the bowls of the carb and remove the smaller line that goes on top of the carb because my 35 carb i purchased used didn't have that feature. I honestly preferred it over the manual choke system on the carb it was a easier start. Also I'm running my fuel like the motor says for the most of it 100:1 I add just a splash extra but not a noticeable amount and haven't had a lick of trouble yet

 

[Dano3578]

Ok, test 2 and still not running right. Fresh plugs, fresh fuel, mixture screw 1-1/2 out
Cranked her up second pull, idled great , took off and still not running at full capacity. Stopped in the middle of the lake, checked plugs, top plugs was clean and wet, bottom plug was black and wet. I'm second guessing if the plugs are even being filed.

I'll be checking compression with gauge, checking/changing thermostat, checking timing/3/8 or more spark jump, and other test on electrical this weekend. Any other feed back would be greatly appreciated

Bowfisher, my second hand carb I picked up didn't have fittings on it to keep manual primer system.
Fuel mixture- I read on more than one thread that the 100:1 mixture was a screw up by the manufacturer.

 

[bowfisher2636]

Ok, test 2 and still not running right. Fresh plugs, fresh fuel, mixture screw 1-1/2 out
Cranked her up second pull, idled great , took off and still not running at full capacity. Stopped in the middle of the lake, checked plugs, top plugs was clean and wet, bottom plug was black and wet. I'm second guessing if the plugs are even being filed.

I'll be checking compression with gauge, checking/changing thermostat, checking timing/3/8 or more spark jump, and other test on electrical this weekend. Any other feed back would be greatly appreciated

Bowfisher, my second hand carb I picked up didn't have fittings on it to keep manual primer system.
Fuel mixture- I read on more than one thread that the 100:1 mixture was a screw up by the manufacturer.

This is going to sound like the dumbest question but are you over heating? Is it pushing enough water out?

 

[Dano3578]

Very good water pressure. I'll know more over the weekend after doing some exstinsive testing

 

[Dano3578]

Update.......
When I first started working on this motor 3 weeks ago, I had spark on both plugs. As mentioned in the beginning of this topic, morer ran great for 5 minutes then sluggish. Thinking I had a fuel issues, cleaned carb again, and took her out on the water. Did the same as first test run. After third test run yesterday, I noticed one plug really clean( like not firing). Ran sluggish from get go.
Today I checked spark again to find NO spark on top cylinder. Moved plugs and plug wires around to rule that out. Swopped leads coming from power pack to coil around to rule out my coils. So....... That leaves me with a bad power pack or something under the flywheel. I'm guessing.......


As good as I can, again I looked over everything electrical without pulling flywheel off to make sure nothing was shorting out or damaged. Didn't see anything. Any advice would be greatly appreciated.
How do I rule out the power pack before pulling flywheel?

 

[flyingscott]

www.cdielectronics.com has the test procedure for the powerpak.

 

[Dano3578]

Thanks flyingscott. I looked it over and haven't found what I'm looking for. Really small font. I'm on iPhone

 

[Dano3578]

Actually Scott I have no clue what they're talking about on there. No too swift when it comes to electronics. From what I'm gathering, there's no other way to check power pack WITHOUT stabbing wires with test light or cutting wires and splicing back together? I read something about putting test light to the different terminals inside plug coming off the stator. But to me that would only be testing stator mechanisms because the power pack would not be hooked to anything else

 

[Dano3578]

Thanks for all the help

 

[jasper60103]

Thanks for all the help

Did you figure it out?