Need help with 15hp seahorse

[fishon1213]

I have a mid 80's Johnson Seahorse 15hp that I need some help with.
My brother replaced the head gasket and it ran for a few minutes, quit, and has not run again.
I got the motor and started from scratch.

It is getting fuel, I even went as far as to put a little in the cylinders but it did nothing.

It has good spark on both cylinders, tested with a spark tester

The compression test gave me 90, 95. Kinda low huh?
I pulled the plugs and they looked to have fine, black powder on them. Metal?
I pulled the head and it had the same stuff on the inside.
The head gasket appeared not to have failed.

Whats the next step experts? Rebuild?, Rings?

 

[mars bar]

Re: Need help with 15hp seahorse

Squrit some heavy oil in the cylinders and do another comp. test , If the numbers are higher than yup your rings are shot.

 

[fishon1213]

Re: Need help with 15hp seahorse

I squirted some oil in and compression went up to 120.

So just hone and rings maybe? How big of a job is that?

 

[AlTn]

Re: Need help with 15hp seahorse

was the spark tester an open air gap tester set to 7/16" and the spark jump was blue?...if so....I'd pull the flywheel and check the key..if it's sheared the timing will be off and the motor won't start....90 and 95 lbs. compression is sufficent for the motor to run pretty well...in fact, get it running and do a decarb treatment as outlined in the Top Secret Files..and the compression may come up some....you've established compression, next establish spark of 7/16"...then move onto fuel/air mix....most auto parts stores have that type spark tester for ~$10 or less...btw..how to the cylinder walls and pistons look?

 

[fishon1213]

Re: Need help with 15hp seahorse

The pistons move when you turn the flywheel so the key cannot be sheared right?

I am going to test the spark more thoroughly after the sun goes down a bit.

Thanks.

 

[dew2]

Re: Need help with 15hp seahorse

NO Not right pull the flywheel.Only way to see if the key if broke,twisted or damaged.

 

[Will Bark]

Re: Need help with 15hp seahorse

No, the torque of the flywheel nut can be tight enough to turn the crankshaft and the key could still be sheared; you need to mke certain that the key is still intact.

 

[AlTn]

Re: Need help with 15hp seahorse

the flywheel is a taper/friction fit to the end of the crankshaft..the flywheel contains a magnet which induces your spark...if it's off at all, your spark won't arrive when needed...if the flywheel were so loose you could turn it w/o the pistons moving, it would have launched itself into the next county

 

[fishon1213]

Re: Need help with 15hp seahorse

So 90psi is enough that it should run? Well then, its got compression, spark, and fuel, and doesn't run. So maybe it could be a sheared key. It does rarely act like it wants to start. I'll see about getting a puller to get the flywheel off.

Actually the more I think about it, a sheared flywheel key makes more and more sense. Maybe its just that I want the cheapest, easiest fix. The pull start takes some force to pull as usual but you can turn the top of the flywheel by hand very easily. Is that a sign of anything?

 

[fishon1213]

Re: Need help with 15hp seahorse

Well, I pulled the flywheel and the key is not sheared. So much for the cheapest fix.

I am still leaning towards spark as my problem. Poor and intermittent spark would probably cause the carbon buildup I am seeing in the cylinder right? Both cylinders are equally dirty. Doesn't appear to be metal though and the cylinder walls look fine.

I am thinking since both cylinders seem to be having issues it would not be a coil unless both went bad, unlikely.
Any tips next?

 

[mikesea]

Re: Need help with 15hp seahorse

disconnect the kill button if you have one,they can be intermittent Is it possible that your flooding?sometimes the fuel pump will blow and that can cause too much fuel going into eng via the pulse that operates the diaphram in the fuel pump.If your plugs look super wet,it could be the problem,the older engines are prone to have failures in fuel pump with new fuel,not to mention they wear out over time

 

[Tim Frank]

Re: Need help with 15hp seahorse

Going back to your OP....why did the head gasket need to be replaced....i.e. what led up to it?

 

[fishon1213]

Re: Need help with 15hp seahorse

I really don't know why my brother replaced the head gasket. I think he was having issues(don't know what) and misdiagnosed, so it probably did not need replaced. I got the motor and just tried to start over.

I will check the key/kill switch, ect. This is a low profile motor with electric start so the solenoid and some other wiring is mounted to the transom, not cool. I would just assume get rid of all of it and use a push button start as it only requires two wires. I have some cleaning up to do with all of that wiring anyways.

 

[Tim Frank]

Re: Need help with 15hp seahorse

If you can find out why, it might be significant.

 

[fishon1213]

Re: Need help with 15hp seahorse

I just talked to him and he said the motor started running poorly, he did a compression check and replaced the head gasket because he thought 90psi was too low.
I have a 35hp evinrude that has 110psi with the same comp. tester and runs great so I would think this motor would at least fire.

I put clean plugs in, that did not help.
I disconnected the black/yellow wire from the ignition(kill switch?), that did not help.
I swapped the power pack with one from a running motor, that did not help.

 

[OLDIRON]

Re: Need help with 15hp seahorse

That 15 should run on 90-95 lbs. I know this may be a reach, but are you sure the sparkplug wires are not crossed? I've seen it happen before.

 

[Tim Frank]

Re: Need help with 15hp seahorse

was the spark tester an open air gap tester set to 7/16" and the spark jump was blue?... establish spark of 7/16"...then move onto fuel/air mix....most auto parts stores have that type spark tester for ~$10 or less...btw..how to the cylinder walls and pistons look?

Did you ever respond to this?

 

[raczekp1]

Re: Need help with 15hp seahorse

i had low compresion in one of my motor/#60 PSI/, motor even didnt suck fuel from the carb, so i think low compresion prevent from sucking fuel from carb.
shot some WD 40 in carb troath, and try to start.if motor response so it means your problem is in carb side

 

[fishon1213]

Re: Need help with 15hp seahorse

Tim Frank,
I do not believe I am using the correct type of spark tester. Mine is an inline tester which I thought was sufficient. I will get a hold of the correct type of tester and let you guys know what happens. Plug wires are not crossed.

BTW Thank you everyone for your time and advice.

 

[Tim Frank]

Re: Need help with 15hp seahorse

I'd wait and hear from someone about the in-line tester.
I don't know anything about them, but it may well be fine...or is there no open gap?
The open gap type are less than $10-.

And I think the poster meant are the plug wires "swapped"....i.e. wrong wire on wrong plug.