1978 Johnson Seahorse 115hp

I was on the lake one day, doing aroung 35mph, when the motor droped down to 25mph at full throttle, and it still don't go faster,, sorry, new to boating, what could be the issue? Also, what is the "Throttle Friction?"

Re: 1978 Johnson Seahorse 115hp

Throttle friction is a knob on the control box (possibly a screw) that sets tension on the throt. cable so it will hold position without continous pressure.
As for the slow down, sound like you lost 1 maybe evn 2 cylinders (fire).
Pull plugs and inspect them...see if they are all very close in color-med. brown to dark brown-then do a compression test if you can.
If you have a tach, did the RPM drop significantly??

Re: 1978 Johnson Seahorse 115hp

Tach is not working, and how do you do a compression test?

Re: 1978 Johnson Seahorse 115hp

you will need to buy a compression tester if you do not have one also your compression should range from 90-130 or more.

Re: 1978 Johnson Seahorse 115hp

I am trying to get my tach working again. Here is the problem. From behind the tach is two wires, yellow and black. The black is hooked up but the yellow is not. the yellow is connected to the tack, coming out it is cut, the good news is there is the other half coming out of the throttle control. From the throttle control it is coming out and going to the back of the boat toward the motor, the problem is, it is cut half way to the engine with the other end no where i sight, my question is this, where on the engine does it go? I have a Johnson Seahorse 115hp 1978. Where on the engine does it connect? To the rectifier and where on that? On the rectifier there is three wires, 2 yellows and a red going to a thing that has a bunch of screws that the yellows and reds are screwed into, does it go there? Can anyone help? I am trying to hook up the tach so i can see if it is working and if i have a drop in RPM's. Thank You

Re: 1978 Johnson Seahorse 115hp

There should be a gray wire from the engine that ends inside the control box. That is the tach signal wire from the engine. It should go to the S (signal) terminal on the tach. All you need are a battery pos and negative-usually from some other gauge on the dash. Check for loss of spark with an inductive timing light. Check all 4 plugwires. Weak ignition components tend to fail when the engine gets up to normal operating temps. You can probably rent a compression gauge and timing light from a local auto parts store.

Re: 1978 Johnson Seahorse 115hp

I found the grey wire that is coming out of the throttle control, it has a yellow wire that is crempted into it, the grey is really short and i guess the yellow is using it to extend the grey, anyway, i hooked it up to the wire coming out of the tach, still nothing, also, coming out of the throttle control box next to the grey is a black wire, any idea what that one is? Thanks for all the help, just a little more please

Re: 1978 Johnson Seahorse 115hp

Your box is only factory wired for the grey tach wire. Don't know what the black is in 78. Later boxes had a black which was ground, but not in 78. You will have to find a + and - hookup from one of the other dash gauges. You may also want to hook up the tach light for night operation.

Re: 1978 Johnson Seahorse 115hp

do i take the grey wire from the control box and hook it up to the wire coming out of the back of the tach? Cause that didn't work. I understand that i need to hook up a wire to on of the other gages + and -.... but what wire coming out of what? Do you know what i mean? Also, in a 75 Glastron, there are 3 gages,, Tach, Speedometer and fuel gage, which at this point only my speedometer works. don't get me wrong, this is a nice little boat, just needs this little repair job done. and beleive it or not, i am getting an education on how to work on it Thank you again and sorry for all the dumb questions and lack of understanding answers sometimes, but if you could see it, well, you know what i mean.

Re: 1978 Johnson Seahorse 115hp

Most tachs have four electrical connections. One for the light-usually a wire to the bulb. Then you may have either a wire harness or a sparate screw-on terminals for the other 3 inputs: signal, positive and negative. It depends on what tach you have as to whether you have screw on terminals or a wiring pigtail out of the tach. There are usually two long brass screws which are used to hold the tach into the dash with a large u-clamp. Usually one of these is a ground. I have seen the other being the positive-only if the u-clamp has an insulator where it fits over the brass screws. You might want to post a picture of the back of the tach...

Re: 1978 Johnson Seahorse 115hp

Sounds like you have an older, Airguide Tachometer, which had just the yellow and black wires. The black lead goes to an engine ground, the yellow to one of the yellow leads off the rectifier. If the rectifier is not working, the tach won't work.

The gray wire should provide the signal for the yellow wire if you have continuity, and you should be able to pull the engine ground from the small M post on the ignition. It might just be easier to run new wire from the engine's terminal block.

Look carefully around the rim of the face of the tachometer and you should be able to identify the company that made it. .

Re: 1978 Johnson Seahorse 115hp

Well, here is an update, i tried everything with the Tach, still not working, got the fuel gage working, so i am getting a new rectifier. Now, back to the real issue.
We had the boat at the lake once again, after riding around for less than an hour, the speed went from 30 to 35 to 20 mph. I let the boat sit and idle for about 10 min or so, then BAM, we had power again, it lasted most of the day, then, we stopped and had lunch, let the kids fish off a dock for about an hour, then we took the boat out again, first we let it warm up, then BAM, we had no power once again, we called it a day, the funny thing is, the first time we had no power, the speedometer did not work, but when the power came back, it was working, i think that was just a fluke but maybe not. Any ideas, i have not run a compression test yet. But when i do, and there is low compression, what would that mean, engine rebuild? Can anyone let me know why we had no power, then had power most of the day, then back to no power? Any ideas, Thanks again for everyones help, Again.

Re: 1978 Johnson Seahorse 115hp

You could be dropping a cylinder once the engine warms up. Weak ignition components tend to fail when the engine reaches normal operating temps. Once the weak ignition component cools, it may work again. You could test for strong spark on all 4 plug wires when the engine drops speed. An inductive timing light is handy to check spark in this situation.

Re: 1978 Johnson Seahorse 115hp

Ok, got compression tester and did the test,, let the motor warm up, pulled plugs and started motor 7 times on each plug, here is the readings i got::::: 90-105-100-100. How are these numbers? If they are ok, what else can i try,, cleaned the fuel filter, which did not look like it needed it..

Re: 1978 Johnson Seahorse 115hp

You have one cyl which is marginally low, but perhaps not a condeming problem at this point. You may want to decarb the engine and see if that low cyl compression improves. An inductive timing light will show the condition of the spark. Check each plug wire for spark when the engine starts to slow down or have no power.

Re: 1978 Johnson Seahorse 115hp

DeCarb the motor? Is there a good web site link or something to tell me how to do that and what tools i'll need to get to do a decarb? Sorry if i sound dumb, i am able to do the work even if i'm new at it, anyway, thanks again and any instructions will be help.

Re: 1978 Johnson Seahorse 115hp

An early advocate of decarbing outboards is Captain Bob Dunkleberger, a marine surveyor from New Jersey. Here's his method:

"This works for Carbed, EFI, Ficht, HPDI, Optimax and even 4 strokes...
First you need a separate small fuel tank. One of those 3-gallon red Tempos works well or an empty gallon milk jug in a pinch, but it might be a bit messier.

I use Seafoam over the OEM stuff like OMC Engine Tuner or Merc Power Tune because in the last few years they changed the formula and you have to let them sit up 12 hours. Who's got time for that? Seafoam does the job in 15 minutes and can be purchased from NAPA, Car Quest or other auto stores.

You'll need 3/4 gal of gasoline and one 16oz can of seafoam for each engine. Don't forget to add 3oz of oil if you are premixing in a carbed engine. Use about 3 ft piece of fuel hose off the little tank. You connect this tank to your engine by pulling off the main tank fuel hose off the intake side of your water separating fuel filter and plug the hose off the small tank on to that fitting. Or you can separate the fuel line on the tank side primer ball, so you can still use your primer. If you have an engine that has fuel plug then you need a fuel plug on the little tanks hose.

Start the engine, let it warm up and start pulling the mix into the engine. You may have to increase the idle to keep it running once she get loaded with the Seafoam. Run the engine 15 mins in the dock or just cruising around under 2500. Then shut it down and let it sit for 15 mins. Restart the engine, the smoke you see is the carbon burning off. Do the whole thing again and let her sit again for 15 mins. If she smokes after the second time do it again, but I've never seen one still smoke after three doses. The gallon mix should be enough to do this 3 times. You don't need any wide open throttle, you don't need to change the plugs. If it's cleaning the combustion chambers it's also cleaning the plugs, but every 50-60hrs is good time to change plugs in most engines.

I cleaned a antique evinrude one time that had a 1/4" of solid carbon on the exhaust chamber walls by running a 1/2 gal of the mix through it. Seafoam has been around since the 30's and it's what they used when they were burning straight 4 stroke 40SAE oils in outboards.

You guys with the 4 strokes think you are immune from this? Those engines work 10 times as hard as any auto engine ever will and they will carbon up. I bought a Bronco two years ago that had 95,000 miles on it. When I used seafoam on it I had the neighbors hanging out of their front doors looking for where the fire was after I started it the first time there so much smoke.

Too many are under the assumption that it's totally the 2 stroke oil that causes the carbon, Wrong... it's also the additives they put in the fuels today. The carbon inhibitors in 2 stroke oil are there for this reason also. Remember when gasoline used to smell like gasoline, today it smells more like bad cologne.

For those guys that like to do the carbon treatment by spraying it down the carbs Seafoam also comes in spray can called Deep Creep. It's the same stuff under pressure. Says right on the can Oxygen Sensor Safe, for you Yam guys.

After that, if your engine manufacturer recommends a daily additive treatment then do so. The tank and hose are a one-time purchase and the Seafoam is only costs $5-6.00 per can. It is too easy not to do it."

Re: 1978 Johnson Seahorse 115hp

WOW!!!!! That is awsome!!! I am going to try that ASAP. Just one more question,,,, I have been reading about the spark plugs and gaps. All the web pages and post on here are saying for a Johnson 115hp 1978, it is recommended to use a Champion QL77JC4 at a .30 gap. While i was running the compression test, i noticed that there were Champion L77J4 plugs in my motor, i havent checked the gap but eyeing it looks like around .30 (geez i don't know LOL) but there is a gap in it. Will these plugs make any difference in the loss of power? Also, there is an dark greasy oily stuff on the plugs, does that tell you i need to decarb? And should i get the QL77JC4 Plugs at a .30 gap? Thanks again, the last post you sent me is great, just want the doc ordered, new plugs or not, i am going to decarp the motor.
Tom

Re: 1978 Johnson Seahorse 115hp

ok, i did the carbon cleaning with the seafoam, here is the results. I am still smoking a little, the idle is rough and there is gas coming out of the front part of a plate that is in front of the carbs, i didn't use that much seafoam, what is going on? I am pretty sure it is gas because i used alot of gas, just letting it idle while doing this, plus, in the back of the boat where there is a drain, it is filling up with a black liquid that smells a little like gas,,,,,,help!!!!!!!!!!!

Re: 1978 Johnson Seahorse 115hp

We had a 115 Sea Horse V4 brand new, and they were "well let me say" "Crappy"

Headland piston rings, (The top piston ring tries to jump out of it's groove)

2nd blow up!

1st blow up!

Was #1 head gasket.

That was in 4 years of ownership, the Yamaha replacement (1984) Hasn't blown up since. Still running to date.