1978 johnson 15 hp seahorse MOTOR FROM HELL

[Larry Tate]

hey guys the guy i work for bought a 1978 (I think) johnson seahorse short shaft from "some dude" for $75. i know, i told him from the start it was most likely a bad move. he replied, "the guy said it ran fine last year and he couldn't get it to start this year." i bet. soooo......
1. got it to run. seemed to be ok (for a $75 motor) but was no tell tale and wasnt pumping water. fixed that...
2. my buddies dad takes it out and when he puts it back inside the lower unit is leaking oil. it needed a seal kit. fixed that...
3. wouldnt run at bottom of throttle. when in neutral it wouldnt idle much under 3/4 throttle, under no load. uh-oh....

pulled the carb apart. cleaned as much as i could with a big can of carb cleaner, everything else looked good. made sure float pin and idle screw were in working order. they were.
still not going right. repeated the last step of taking the carb off and apart again, made sure everything was right. it was, and still nothing. replaced a old section of fuel line from pump to carb that looked nasty, and that wasnt it. one coil was newer and one looked like it was 20 years old. replaced the older one, and no difference. at that point i kinda threw my hands up and said ok i need help. HELP!!!!! haha thanks guys

 

[Whoopbass]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

Part the p.o.s. out on ebay. You will easily make $300 from it before ebay fees.
Try soaking the carb overnight in cleaner and then blowing it out with compressed air.

 

[lindy46]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

Did you install a carb kit? Did you clean the idle circuit under the core plug at the top of the carb?

 

[Larry Tate]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

idle circuit? core plug? enlighten me please.

 

[JDusza]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

Couple things... don't give up. Sounds like you are very close and all you really need to do is ensure the low speed circuit of the carburetor is repaired.

There's a Welch plug on top of the carb (about 8 mm in diameter) that hides the machined holes making up the low speed jets, the low speed circuit. These holes have to be c-l-e-a-n. You can access them through the carburetor venturi behind the throttle butterfly with a small wire if you do not want to pull the welch plug. They are on the top side of the carb. Two behind the butterfly, one in front, about 0.015" in diameter, but they are not all the same diameter. Be mindful that cleaning them this way may still leave some junk in the chamber under the Welch plug that can float around and re-jam you. That is why removing the plug and cleaning from the top is advised.

To remove the plug, gently drill a hole through it, being very careful not to hit bottom when you go through. Insert a bent nail or the like and pull the plug out. Voila! Low speed jets, the idle circuit mentioned! Clean then replace the plug. A replacement plug is part of the carb repair kit. To install, locate the new plug, get a punch of just slightly smaller diameter than the plug and flatten out the new plug to seal it in place; easy, but be careful not to whack it so hard you crack something.

You can do it! It's easy!
J

 

[Larry Tate]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

damn thanks man we were about ready to give up on this thing...will try that soon. know the best/cheapest place to get a carb kit for it?

 

[1946Zephyr]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

Here at iBoats or at any OMC dealer.

 

[Whoopbass]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

Iboats is as cheap as anybody for a carb kit.
SOAK the CARB for a day or two in Pine Sol. Clean it with carb cleaner and then blow it out with air.

 

[Larry Tate]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

ok will get a carb kit here at iboats...thanks guys will post back with results.

 

[Larry Tate]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

ok so i just pulled the carb apart to rebuild with the kit i got. i replaced the float pin and the clip it attaches to, the removable jet that the float sits inside of, and the gasket for the bowl. all of these things seem to be in ok shape from the looks of it. i pulled the welch plug on the top of the carb off... nothing but 3 little holes inside that are perfectly clean. i mean not one little bit of dirt. so if there is anything else u guys can suggest why this thing is being so ridiculous while the carb is apart that would be great. also, would it be better to re-install then new plug in concave side up or down? thanks again guys

 

[dazk14]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

Do you have compressed air with a rubber nozzle?

You need to blow out those 3 "clean" orifices(holes). Often there's shmutz that is clogged at the outlet.
A few approaches to do that AND verify they are functioning.

If welch plug left on, load the load speed circuit with carb or brake cleaner through the idle mixture threaded opening (needle removed). Run air through opening, hold open throttle butterfly, verify 3 SMALL orifices shooting out fuel looking from rear of carb down barrel.

Welch plug off, put air through each orifice from the welch plug opening, put finger through back of carb, open throttle, feel air running through each "hole". As noted, the throttle butterfly must be opened to get access to the openings in the carb bore from the rear - if that makes sense.

Eventually, the best way to ensure they're clear is to force some brake/carb cleaner through those drilling, so you can visually verify. Since the welch plug is off, use the straw from your carb/brake cleaner to shoot through the 3 "drillings" (1 at a a time).

Jdusza pointed out the exact location to see these 3 TINY openings inside the carb.

 

[AlTn]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

if you haven't already done so google.. Leeroy's Ramblings...outboard motor related articles..9.9/15 hp...read up on carb rebuilding and the link and sync procedure...he's written extensively on this series of motors

 

[Larry Tate]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

ok thanks... welch plug install concave side up or down?

 

[AlTn]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

you install it up then use something < I use a 3/8" drive extension > to expand it by striking it in the center of the plug..before install put some sealant around the outer edge of the plug<silicone or rtv aren't good choices>

 

[F_R]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

By now, it should be obvious that the carburetor is not the problem at all. Go ahead and put it back together, and if it isn't any better, back up and do what you should have done in the first place. That is, you should have diagnosed the problem instead of just assuming it was the carburetor.

Did you check the compression? Was it overheated from running with that non-working water pump? If it was, did you replace the head gasket and exhaust gaskets? Did it score the piston skirts and rings? How is the crankcase pressure? Perhaps the fuel pump diaphragm is holed, squirting raw fuel in the crankcase? Of course you did try a couple of new spark plugs, didn't you? (The biggest problem the 15hp had was fouling plugs)

 

[BoatingCop]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

It's toast...you should send it to me, I'll pay shipping!! lol just kidding! The 9.9/15's are my favorite, and IMO most indestructable engines made if maintained corectly. Remeber, the only basic things needed to run are fuel, spark, and compression. What are your compression numbers?

Also, you should REALLY look at Leeroy's Ramblings. It will tell you how to do almost anything with these engines. Its very detailed with lots of pictures. Keep at it. You got a hell of a deal on a GREAT engine.

 

[nwcove]

Re: 1978 johnson 15 hp seahorse MOTOR FROM HELL

convex side up