Johnson 20 hp Seahorse no power at WOT

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AlTn

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Re: Johnson 20 hp Seahorse no power at WOT

run a piece of clear fuel line or clear vinyl tubing from the fuel pump to the carb and look for air bubbles in the line while running...if no bubbles and the line remains full of fuel mix...your fuel pump isn't the problem. If bubbles or air pockets are present, your pump, connections all the way to the tank, or the tank itself may have problems. Is the primer bulb remaining firm while the engine runs?
 
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chiefcatchemall

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Re: Johnson 20 hp Seahorse no power at WOT

yup the primer bulb remains hard as a rock the whole time its running.
 
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AlTn

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Re: Johnson 20 hp Seahorse no power at WOT

in time, while running, the bulb should soften as it becomes part of the fuel line in essence
 
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chiefcatchemall

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Re: Johnson 20 hp Seahorse no power at WOT

AlTn said:
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.
Click to expand...




I just noticed this post. I meant to clean the ground under the armature plate, but now that I think of it I dont believe I did. Thats about the only thing thats not clean!
 
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chiefcatchemall

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Re: Johnson 20 hp Seahorse no power at WOT

Well I went through and cleaned all the grounds up real nice. Went back through and re-gapped the points. Fired right up on the first pull like she usually does. But I have the same problem. I get the initial jolt of power at WOT for a brief moment then she bogs down to about 1/3 power. All the electrical is new, and I mean all of it. I get a great spark on both cyls. I am now convinced it is not electrical related. I believe it may however be fuel related. I did notice that she surges and drops down a lot in rpm's. It consistently does this. And from what I understand this points to a dirty carb? Ive been through it a million times. Cleaned the heck out of it. Blew it out with air. Should I go through it again? Could this be my problem?


This is strange because when I pull the top plug lead off it doesnt make much of a difference. But when I pull the bottom plug lead off it makes a HUGE difference but it didnt die. This is why I originally thought it was electrical. Is it possible I just am not getting the proper fuel to the top cyl? Too much or too little?
 
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chiefcatchemall

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Re: Johnson 20 hp Seahorse no power at WOT

Forgot to mention pumping the primer bulb makes no difference at all
 
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tx1961whaler

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Re: Johnson 20 hp Seahorse no power at WOT

The carb feeds both cylinders, so if one cylinder is getting gas the other one is also (theoretically).
This is grasping, but look for a crack in the crankcase. Surging implies air leaks.
 
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oldman570

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Re: Johnson 20 hp Seahorse no power at WOT

With the motor running and only half WOT spray WD 40 around the motor gaskets and crank seal one spot at a time and see if the motor revs up any. An easy way to find air leaks. Be sure not to get any near the electrial and carb throat as it could mess up the electial and the motor should rev when shot into the carb. The crank seals could be leaking and causing the problem,as I've had to replace a few myself on motors like yours if they have set for some time and the seal dryes out and cracks.
Worth a Try.
Oldman570
 
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chiefcatchemall

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Re: Johnson 20 hp Seahorse no power at WOT

Thanks for the responses. Last night out of nowhere my motor decided it would only run with the choke on. So I figured dirty carb. So this morning I went through and cleaned it up and re-set the float. Put it all back together and now it will only run for about 2 seconds then die. I am officially done with this motor. I replaced just about everything under the sun to make this motor like new and now I cant even get it to run. If anybody wants a 73 seahorse 20 hp its theirs. new coils,points,condensers,all new wiring,head gasket,recoil starter,and impeller. Have it, Im not putting another plug nickel into it. DONE:facepalm::(
 
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doc7

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Re: Johnson 20 hp Seahorse no power at WOT

i think you have poroblem with crankshaft seal. if choke helps to start it is more then possible.
 
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Will Bark

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Re: Johnson 20 hp Seahorse no power at WOT

Before you junk it, you have not mentioned the reed valves; have you looked at them to see if any of the leaves are damaged or not seating correctly?
 
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chiefcatchemall

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Re: Johnson 20 hp Seahorse no power at WOT

i have not. ill take a look but im about more than fed up with it. UGHHH
 
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oldman570

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Re: Johnson 20 hp Seahorse no power at WOT

Go to http://www.leeroysramblings.com/ and there you will find almost everything about your motor and what could cause the trouble you are having and how to fix it. When you rebuilt the carb did you remove the small welch plug and clean out that passage and replace it with the one sent in the kit and put a good sealer on it before tapping it in? Some kits are sent with a gasket that goes between the carb and block, with a small hole in them, and is needed on some application and not others that needs to be checked.
Don't giveup yet as those motors are better than the newer ons being made. JMO Once you get it running you will be happy with it and know every little quirk it has. Relax and leave it sit for a spell and go back to it latter when you are refeshed. Things will get better.
Oldman570
 
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chiefcatchemall

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Re: Johnson 20 hp Seahorse no power at WOT

Yup I sure did remove the welch plug and go through the small passages. I used finger nail polish as a sealant. I will be taking a look at the article here in a bit. Thanks guys
 
kfa4303

kfa4303

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Re: Johnson 20 hp Seahorse no power at WOT

fingernail polish as a sealant? how? where? why? you don't want/need to seal anything up in the carb. On the contrary, you want all passages unrestricted and fee of debris, especially the tiny holes found beneath the welch plugs in the carb. The welch plugs are dry fitted into place and then seated turning them from a slight convex profile to a flat disc. As for the fuel primer bulb, it should get hard when squeezed prior to start up and then become soft as the motor operates under normal conditions. If the pump is not getting firm, the primer bulb itself may be bad, or the fuel pump is bad.
 
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chiefcatchemall

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Re: Johnson 20 hp Seahorse no power at WOT

I just used a very light coating around the outside of the plug. Ive heard of guys doing this before and figure it couldnt hurt. The bulb is firm and holds pressure good, and did become a little softer when I had the motor running.
 
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madcircle

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Re: Johnson 20 hp Seahorse no power at WOT

i just got my boat back from a local marine and the first time i put it in the water I had the same problem. Needless to say, it is going back there tomorrow(it was there for what ended up being a power pack. When I called to tell them the problem he asked me to pump some fuel into a clear container to check for water before I brought it in. If you have a water separator maybe check that too? After I get my boat back I will let you know what they found.
 
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