Help with 1960 Johnson 18hp Seahorse

Zapit2um · Dec 3, 2012

Needing some help diagnosing a problem with my motor. As the title says I have a 1960 Johnson 18hp seahorse.. It was running like a champ and was getting about 18 to 19mph out of it then it seemed to lose a little bit of power, I checked the speed and I was down to about 14 to 15 mph. It ran like this for about 5 minutes then lost almost all the power, was doen to 5mph at best. I tried adjusting the high speed idle but it didn't seem to help. When I have it in neutral with the throttle wide open it seems to be running fine, by that I mean the rpms seem to be there, it's screamin. But when I put in gear and throttle it up.. nothing 3 to 4mph at best. I cleaned the plugs and regapped them tried new gas, nothing seems to help.

kbait · Dec 3, 2012

Re: Help with 1960 Johnson 18hp Seahorse

If you pull the recoil medium speed, and you feel a good 'whoomp, whoomp', you likely have adequate compression for both cylinders. Check spark, and be certain that you're getting 1/4" blue bolt from both leads. If so, install new J6C plugs gapped to .030" and try again. If it's only firing on one cylinder, it'll seem to run just fine in neutral, but only go about 1/3 speed. If it still runs the same w/verified spark and new plugs.. check compression w/gauge to be sure it's good, and pull and clean carb.

Don't over-rev your motor in neutral, or you may suddenly have a new top-speed of zero.

Good luck!

steelespike · Dec 3, 2012

Re: Help with 1960 Johnson 18hp Seahorse

A quick check for spark pull one plug wire at a time and see if it will run.
if it won't run on one of the cylinders could be lack of spark.
If the coils haven't been replaced recently they both are suspect.

HighTrim · Dec 3, 2012

Re: Help with 1960 Johnson 18hp Seahorse

Is this motor new to you, or have you had it for a while?

As stated, is this an original igntion, or have you updated it?

If the coils are original, they are 100% shot.

Zapit2um · Dec 3, 2012

Re: Help with 1960 Johnson 18hp Seahorse

Motor is new to me. Here's what I did. I fired it up let it run for a minute then disconnected the top spark plug wire and it died. I hooked the wire back up re-started it and unhooked the lower spark plug wire and it kept running. I then switched the plugs around, just to check them, and had the same results as before. I'm guessing the bottom cylinder isn't getting fire.

Thoughts?

HighTrim · Dec 3, 2012

Re: Help with 1960 Johnson 18hp Seahorse

Pull the flywheel, time to go over the ignition. If the coils are cracked and deteriorated, they are original and need replacing.

Dress and clean the points with acetone, and set at 020. Condensors should be checked as well. If plug wire is original, I would replace it when changing coils.

If ignition has been updated, may be a matter of cleaning and regapping points, or may be a faulty connection in plug boot, something simple.

freddyray21 · Dec 3, 2012

Re: Help with 1960 Johnson 18hp Seahorse

it's dropped a cylinder either a coil or a condenser is bad

Zapit2um · Dec 3, 2012

Re: Help with 1960 Johnson 18hp Seahorse

I've taken the starter rope off and have removed the nut to the flywheel. Should the flywheel just pull right off or is there something else I need to do? Do I need a flywheel puller?

HighTrim · Dec 3, 2012

Re: Help with 1960 Johnson 18hp Seahorse

You need a harmonic balancer puller. Available cheap at harbour freight or princess auto depending if youre in US or Canada.

There will be an inspection window, removed by taking out the screws holding it onto the flywheel to know what you are dealing with.

Get grade 8 bolts to replace the ones that come with it, they will be junk and break. There is actually a good write up in the Faqs to save us some typing.

EDIT here it is

http://forums.iboats.com/engine-fre...-change-coils-set-points-old-omcs-294072.html

Zapit2um · Dec 3, 2012

Re: Help with 1960 Johnson 18hp Seahorse

Pulled the inspection window and from what I can see everything looks brand new. Will get a puller tomorrow and yank off the flywheel.

Zapit2um · Dec 4, 2012

Re: Help with 1960 Johnson 18hp Seahorse

What's the best way to check to see if the coil is bad? I found this online, will it work the same for my year and make motor?

How to Check an Outboard Motor Coil | eHow.com

HighTrim · Dec 4, 2012

Re: Help with 1960 Johnson 18hp Seahorse

Usually, and I stress usually, regarding the Universal Ignition, you can visually tell if it is ok. If it has been updated, it is likely good.

Now you can test the continuity of the coil, but unless you have a Mercotronic or Stevens tester, which you likely dont, you wont be able to test it with a load on it.

The following is a better site for a description of testing the coils continuity.

Testing an Outboard Coil with a Multimeter using an ignition coil from the Johnson H or T

1946Zephyr · Dec 4, 2012

Re: Help with 1960 Johnson 18hp Seahorse

Do the coil wires look new? Sometimes coils get replaced by previous owners, but the original wires are still in use. It's best to trim off 3/8" off the coil end and 1/4" of the spark plug end, if the original wires are put back in service. You can also swap condensors to see if the spark goes to the opposite cylinder. If so, you may only need condensors. Also check that your points are thoroughly cleaned and re-gapped.

Zapit2um · Dec 4, 2012

Re: Help with 1960 Johnson 18hp Seahorse

I rented a puller from Autozone so I will be pulling the flywheel off tonight. One question, do I use the holes that hold the inspection cover in place to attach the bolts for the puller?

When looking throught the inspection window it looks like I have one red coil (looks new) and one black coil. I'm wondering if the guy I got it from only replaced one of the coils. That's where I am going to start anyway.

HighTrim · Dec 4, 2012

Re: Help with 1960 Johnson 18hp Seahorse

I have never seen a new red coil. Post a pic of it if you can. The newest red coil that I can think of is from '62, they were possibly aftermarket.

Yes, those are the holes that you use. Thread the bolts in 7/16", no more no less. Mark the threads with a sharpie so you know how far to thread the bolts in. Stack a few washers on each bolt. I would leave the nut on flush with the top of the crank to protect the threads, and to keep the flywheel from jumping up in the air when she pops off. If you rap on the center puller bolt, lift UP on the flywheel first.

let us know how it goes.

Zapit2um · Dec 4, 2012

Re: Help with 1960 Johnson 18hp Seahorse

I sure will hightrim. I could be wrong about it being the coil, i just seen a red item and a black item through the inspection window. I will also post pics once the flywheel is removed.

Thanks for all the information, this forum is great!

HighTrim · Dec 4, 2012

Re: Help with 1960 Johnson 18hp Seahorse

What you may be looking at is the condensor.

The older ones had red tops, the new condensors have black tops.

tomhath · Dec 4, 2012

Re: Help with 1960 Johnson 18hp Seahorse

If the contact surfaces of the points look black/burned you might get a spark by cleaning them, but that's the sign of a bad condenser. It's supposed to protect the points from arcing when they open (and they are cheap to replace).

Zapit2um · Dec 4, 2012

Re: Help with 1960 Johnson 18hp Seahorse

Here are the pics. The red coil seems to be older than the black coil.

freddyray21 · Dec 4, 2012

Re: Help with 1960 Johnson 18hp Seahorse

the red coil (which fires the lower cylinder) looks like it has a worn spot on top which it should not have.

Help with 1960 Johnson 18hp Seahorse

Seaman

Commander

Supreme Mariner

Supreme Mariner

Seaman

Supreme Mariner

Commander

Seaman

Supreme Mariner

Seaman

Seaman

Supreme Mariner

Vice Admiral

Seaman

Supreme Mariner

Seaman

Supreme Mariner

Master Chief Petty Officer

Seaman

Attachments

Commander