Johnson 20 hp Seahorse no power at WOT

chiefcatchemall · May 28, 2012

Model number 20R73A. Replaced coils (the one under flywheel and both exterior ignition coils), points, condensers, head gasket, new plugs. I can get it to put along and start up just fine, but have no power when I try to open her up. Seems like it wants to right out of the hole for about 1 second then it just looses all power and will just put along at WOT. Compression reading shows 90 on both cyls. Any idea what this could be. Maybe replace the plug wires? Thats about the only thing I didnt replace...

Will Bark · May 28, 2012

Re: Johnson 20 hp Seahorse no power at WOT

Could be one cylinder not firing @ WOT unplug each wire at a time with insulated pliers when it starts doing that and see if one plug is not firing. Good luck.

chiefcatchemall · May 28, 2012

Re: Johnson 20 hp Seahorse no power at WOT

Thanks I will give that a shot...

chiefcatchemall · May 31, 2012

Re: Johnson 20 hp Seahorse no power at WOT

Well I started her up advanced to WOT in Forward and again I got the initial surge of power right off the bat but it only lasted for about 1 second again. Then she died right down. I found that when I pulled the plug boot off the top cyl it made a very slight to no difference at all. But when I pulled the bottom plug boot off it cut down to about nothing. It is making me believe that my top cyl isnt firing like it should but it still is somewhat just enough to keep it running when I pull the bottom plug boot off...Where should I go from here guys. I cant wait to get this straightened around. She fires right up for me on the first pull every time!!

nwjones18 · May 31, 2012

Re: Johnson 20 hp Seahorse no power at WOT

I'm having a very similar problem with my 25hp Johnson. Looking forward to hearing what you find. I haven't checked the spark yet.

Will Bark · May 31, 2012

Re: Johnson 20 hp Seahorse no power at WOT

You don't mention rebuilding the carb and cleaning out the high speed jet, sounds like you aren't getting enough fuel to the engine. When it just "puts" along have you tried sqeezing the primer bulb to give it more fuel?

chiefcatchemall · May 31, 2012

Re: Johnson 20 hp Seahorse no power at WOT

Carb has been gone through a number of times. Squeezing the bulb does not make any difference at all..

chiefcatchemall · Jun 1, 2012

Re: Johnson 20 hp Seahorse no power at WOT

So where should I start from here guys? Also I have noticed gas on the outside edges of the carb bowl gasket and a little puddle in the carb throat as well. I dont know if these issues are related or not but it is bothering me

bullcity101 · Jun 1, 2012

Re: Johnson 20 hp Seahorse no power at WOT

From what you mentioned with taking the wires off the plug on the top end and not noticing a difference (really 1/2 the power should be taken) seems like either the top cyclinder isn't getting proper spark or proper fuel. Have you gap tested the spark on the top cylcinder? or both for that matter. Should jump bright blue 1/4inch or more. If you find it doesn't have proper spark, try flopping the coils around and see if it makes a difference. Try to narrow down your issue.

slacktidemike · Jun 1, 2012

Re: Johnson 20 hp Seahorse no power at WOT

I've just dealt with a similar problem on a 1940's Johnson 5hp. Found it was a shot, cracked, old plug wire. Maybe you should replace your plug wires. If you do, you might need the solid core, zero resistance type of wire that you get from the outboard shop. I've been told that the modern auto type wires won't work on an old outboard. I don't know if your outboard is newer or older but be aware of the different type of plug wire that your motor might require.

chiefcatchemall · Jun 2, 2012

Re: Johnson 20 hp Seahorse no power at WOT

I am going to go out here in a bit to re-check the spark. I will repost my findings. I am leaning more towards some bad spark plug wire. I have a feeling I am still getting a spark on the top cyl, just a much weaker spark. My motor is a 73 johnson seahorse 20 hp rope start. Can anybody send me a link of where I can get the correct wiring for my motor, or even a local store where I might be able to find some?

Also, if it turns out that this isnt the problem, and it is in fact that I am not getting enough fuel to the top cyl, what would be the root cause of this and what should I be looking for?

Thanks guys, you all have been a real help for my project of restoring my motor. I feel like I am getting real close. Thanks again!!

Will Bark · Jun 2, 2012

Re: Johnson 20 hp Seahorse no power at WOT

If you have a NAPA store in your area they should have the solid core wire you need and even the Auto Zone store in my town has it. NAPA should also have the new ends to hook on to the spark plugs. Good luck

chiefcatchemall · Jun 3, 2012

Re: Johnson 20 hp Seahorse no power at WOT

NAPA in my town was closed today...didnt think they would be..Anyways I got the wire and some different connectors. I got the armature plate re wired, now I gotta bolt it back down and connect the wiring to the exterior coils. Hopefully itll fix the problem. If not oh well, the wires are 40 yrs old anyways, probably a good idea to change them...All the other electrical is brand new

chiefcatchemall · Jun 4, 2012

Re: Johnson 20 hp Seahorse no power at WOT

well I replaced all the wiring. EVERYTHING electrical is brand new...Still has a surge of power for a second then bogs back down like its running on one cyl. So I am assuming my top cyl is either getting too much or not enough fuel. What should I be looking for guys?

chiefcatchemall · Jun 5, 2012

Re: Johnson 20 hp Seahorse no power at WOT

anybody?:facepalm:

AlTn · Jun 5, 2012

Re: Johnson 20 hp Seahorse no power at WOT

chief, with that ignition system < 1 power coil under the f/w and 2 exterior coils , 2 sets of points and condensers > it seems that proper grounding is critical. I've never personally messed with this system, but have noted that other members have removed the armature plate and cleaned and sanded every mounting point for every component and wire. One member swapped the power coil from one side of the armature plate to the other and gained spark on both cylinders. It's also been explained that one set of points acts as the ground for the other during the ignition process so that emphasizes the importance of the grounds. That's the direction I'd go if it were mine. Clean all grounding points to shiny including the threaded mounting holes for all components.

oldman570 · Jun 5, 2012

Re: Johnson 20 hp Seahorse no power at WOT

Check the points on the top if the spark will not jump the test gap of 1/4' the same. If the points are older they can be pited correded more and cause the problem you have. I've had it to where I had to set one set of points at .020 and the other at .017 inorder to get the good spark needed. Clean points are a must along with the gap setting and will effect the runnig of the motor as they will make contact when at idle and make as good when the RPM is increased.
Oldman570

chiefcatchemall · Jun 5, 2012

Re: Johnson 20 hp Seahorse no power at WOT

okay well the points are new and the gap is set correctly...I guess I will go in and take another look at them

chiefcatchemall · Jun 5, 2012

Re: Johnson 20 hp Seahorse no power at WOT

Went through and checked the points again. Everything looked good. I am convinced it is fuel related...When I pull the top plug wire it barely makes a difference. When I pull the bottom you can really tell a difference. Something isnt going right with my top cylinder. At start up it surges and you will hear an increase in rpms then it will bog down and it will do that for a bit before it idles smoothly. When I go to WOT in gear I will get a ton of power then it bogs down to not much power at all. I am STUMPED. This is a list of everything I have done to it..

-rebuilt carb
-rebuilt fuel pump
-replaced points (.020)
-replaced condensers
-new primary ignition coil
-new exterior coils
-new head gasket
-all brand new wiring

Is it possible that something is wrong with my fuel pump? I have tried to pump the primer bulb when running and it makes no difference at all. I am running out of ideas of what it could be. I just want to get it out and go do some fishing!!!!! It has been a nice project restoring this motor that I bought but I am starting to get a little frustrated. When I bought it, it was not in running condition. I bought it cause it looked in good shape and it had descent compression (90psi both cyls.) I can get her to start on first pull very easily. Now if I can get this straightened around I believe I will have a nice little gem of a motor.

Tennessee Cutty · Jun 5, 2012

Re: Johnson 20 hp Seahorse no power at WOT

It's not fuel it's spark. My 18 was just doing the same thing. Have you tried switching plugs around? Recheck your points, mine had all new components too but one set of points (top cyl) was not making good contact across the point faces because the contact faces were not parallel. A little careful bending and they were good. Also replaced plug wires and plugs and my misfiring was fixed. I think it was the points though. It's not fuel related.

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