1975 Johnson 115??

19ftSigna · Apr 8, 2009

Ok, stay with me I know nothing about boats and dont know the lingo...Pleas correct me and help me answer questions that i've got about this motor...my first boat a tri haul 19ft fiberglass.
It has an o/b (out board?) Johnsonw with a 115 on it. Does that mean its a 115hp? Also I bought this boat and my buddy says he got an overheating warning the last time he had it out(last summer), he pulled it from water and replaced waterpump. Never had it back out and sold it to me.
I want to start it up and have no idea how without putting it in the water. How do I start it with a garden hose? I've got a pair of muffles? Also what type of gas does it take, mixed or straight?

Any tips?

Thanks

sheboyganjohn · Apr 8, 2009

Re: 1975 Johnson 115??

The 115 is for 115 hp.

Assuming that you buddy got the alarm and shut it down right away with-out cooking the motor, and the water pump was bad when he replaced it, this might have fixed the problem. Will not know until you run it.

It does not use straight gas, it is a 2 cycle engine so it needs oil mixed with the gas. Be sure to use TWC-3 oil for 2 stokes. This is oil designed for water cooled engines, unlike an old weed wacker that is air cooled.

Going off the top of my head (someone will correct me if I am wrong) the gas to oil ratio is 50/1. If you look on the back of the oil container there will be a chart that shows you how much oil for different amounts of gas.

To run it on the muffs, hook the muffs up to the hose. I slide the muffs on from the side of the engine opposite the prop to cover the water inlet holes. These will be on the side of the motor in the middle behind the prop. You will see a screen behind it so you know you have the right holes. Turn the water on about 1/4 the way, you want flow not a lot of pressure. It will leak out around the muffs, which is o.k.

Make sure you have a fully charged battery. It takes a bit to get these motors turning over. Pump up the primer bulb on the gas line until hard. I would take the cover off the motor turn the key to run (not start) and push in the key and listen for a click at the motor. This will let you know the choke is working. Lift up the warm up lever on the control box, push the key in and turn to start. When it starts let the key out, if it starts to die push the key back in. Once she starts running on her own lower the warm-up lever to slow the motor down. Check to make sure you have water spraying out the exhaust at the back of the prop, and you should get a bit out the exhaust relief ports at the back top of the lower unit. While it is running touch the heads. If they are warm, good, if they are hot, you have more cooling issues to address.

Let us know how it turns out.

Hope that helps.

19ftSigna · Apr 9, 2009

Re: 1975 Johnson 115??

Thanks so much, I do remember seeing on here a guy who was running his o/b motor with his lower end in a big bucket of water with no prop installed, is this possible?

ezmobee · Apr 9, 2009

Re: 1975 Johnson 115??

Be careful doing that 19ftSigna. You have to have it way deeper in the bucket than you think. The water pump in the lower unit needs to be completely submerged to pump properly. So just submerging it till the water intake holes are convered isn't sufficient. The muffs are cheap and work well. Just don't run it much above 1500 RPM on the muffs.

19ftSigna · Apr 9, 2009

Re: 1975 Johnson 115??

ok, i just thought about filling up a garbage can and going that way, think thats deep enough? Where the boat sits we dont have water supply.

ezmobee · Apr 9, 2009

Re: 1975 Johnson 115??

that will probably work. Try to get the water level a few inches above where the lower unit and the midsection meet.

19ftSigna · Apr 9, 2009

Re: 1975 Johnson 115??

pk thanks and i'll try and take some pics, today i'm going to do this so i'll let you all know how it goes.

ezmobee · Apr 9, 2009

Re: 1975 Johnson 115??

Let it run for a while. If your overheat alarm sounds again shut it down immediately. If you let it run a while and no horn then hopefully your cooling problems are fixed.

19ftSigna · Apr 9, 2009

Re: 1975 Johnson 115??

Ok, well we got it running. After about 10 or 15 min of turning the motor over it kicked up and started running. We let it run about 15 min and the alarm went off. We shut it down immediatley. We actually lowered the boat into a pond nearby so the water was not the problem. The heads were hot to touch for a few seconds then really hot. The guy I bought it off of says he replaced the water pump and thermostat. Are there two thermostats? The motor did sound strong though while it was running.

ezeke · Apr 11, 2009

Re: 1975 Johnson 115??

You have only one thermostat (vernatherm). It is rare that you could run 15 minutes with a bad thermostat and much more likely that you need a new water pump impeller.

When you start a motor like yours when cold, the chokes need to be 100% fully closed to enrich the fuel mixture. The only way to be sure that the chokes are closing properly is to have someone crank the motor while you observe the choke plate in the carburetors with the cover off the carburetors. Once you have full choke, starting the engine when cold should not be difficult or time consuming as long as you have a fully-charged battery capable of cranking the engine at 300 RPM.

19ftSigna · Apr 14, 2009

Re: 1975 Johnson 115??

Yeah starting is easy when you close the flaps, then open and hit it. starts right up, finally put the muffs on today and started it up stayed cool and no beeeeep! but noticed that water was coming from head gaskets, so we took off covers and noticed blown head gaskets, everything looked fine inside. No cracks just a little scoring on one cylinder. Worry? or just put some gaskets on and ride it till she bucks? I've only got 500 in the boat, motor, and tailer! I dont want to put a lot of money into this so?

Thanks

ezeke · Apr 14, 2009

Re: 1975 Johnson 115??

Head gaskets often are damaged when the engine overheats and should be replaced whenever it happens; that is not a lot of money, just a little time.

While you are at it, it is very important to inspect the water deflectors whenever you can, because they do move and will always cause an overheat if they do.

Be sure to torque the cylinder head bolts to 14-16 foot pounds, then do it again after the engine has heated up from running.

The cylinder with scoring may be missing a ring on the piston or it may be damage from another cause, but a compression test will usually tell you.

19ftSigna · Apr 14, 2009

Re: 1975 Johnson 115??

Thanks for the info, I ordered the gaskets today from Iboats and should be here thursday, Install friday and test ride saturday!! wish me luck!!