25 hp motor problem

I have a 1985 25 hp Johnson motor pull start. Not electric.That I am having a little problem with and wonder if anyone could give me some insight on it. It started one day when I had run through some weeds and I knew I had weeds on the motor, so I lifted it up and thought I had cleaned them all off, but after going a ways the motor ended up not pumping water and overheated. So I took it home and looked at the gaskets and they were fine, so I put new spark plugs in it and it started right up. Well I did this in the driveway, so I figured it just needed to cool down and would be good. Well I got out on the river and got up river to fish and stopped the motor, but decided to move a little and the motor wouldn’t start. It seems that I can start it when it is cool, but after I run it and it heats up the motor won’t start again until after it cools. Any idea what it could be. Thanks in advance.

Make sure it is in fact cooling. Your impeller may be worn from running out of water. Could also be fuel related. Run a can of sea foam through it.

Just a couple of thoughts here:

Check the water intake ports to make sure there isn’t any junk in there clogging them up. When you said you ran it in the driveway, did you have it in a bucket of water or with “earmuffs” on it so it was getting water? If you run an outboard dry the impeller can be damaged right away. If the motor isn’t getting any cooling it could get hot enough to vapor lock, which will keep it from starting. I’d make sure it was pumping water as a first step.

I went through a similar situation this spring and it was no fun at all. I hope you get it fixed and get back out on the river soon!

Rootski

Sounds to me like a toasted impeller. Takes approximately 29.275 seconds to smoke one when run without water. Asalready stated..check you water inlets, they may have sucked some weeds into them, and then clogged it up. Even if they are clear it sounds like your impeller is toast. If you are fairly mechanically inclined they are pretty easy to change. If not…take it in, but it definately sounds like you need a new one.

Thanks for the help I ran it in the driveway with “earmuffs” on it and it started and seemed like water was going through it. So then I took it on the river and ran it after that and it seemed to run fine and water was coming out like normal, full stream and stuff. Would it still do that if the impeller is toast??? Not a mechanic as you can tell But would like to fix it myself if possible. But I think there is some kind of vapor lock or something that it gets too hot. Thanks again

Sounds like it is OK. I would keep an eye on it though. You may have sucked some junk into it, and when it sat it either dried, or otherwise somehow dislodged. Impellers are pretty straight forward, either they are working or they are not. Sounds like it is at present.
Tuck

Tuck,
I still have the problem though that when I run it for awhile and shut it off, I can’t seem to start it again until it either cools down or maybe there is a vapor lock somewhere that needs to work itself out. Then it will start again. Probably call and ask about it tonight if I get a chance. But it “pee’s” water fine. So water must be getting pumped through it.

Sounds to me like the rings seized the first time it didn’t get water. Although they may not be “stuck” they are scored…or scored the cylinder wall enough to cause you problems when it warms up….A vapor lock won’t continue to happen time after time.

Sorry to say…It’s shop time… In my humble opinion.

Ditto.

I was talking to a buddy and he said something about a coil maybe? Just seeing if that sounds like something. Thanks for the input though.

Although there’s exceptions to every rule…a coil either works or it doesn’t…although sometimes they work at idle and go goofy when moving to a faster speed.

My quarter bet is on the rings/cyliders. I’m sorry to say.

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So then I took it on the river and ran it after that and it seemed to run fine and water was coming out like normal, full stream and stuff.

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Run it!

Keep in mind that just because you don’t have water comming out the “pee hole” doesn’t mean you don’t have water circulating through the motor. New spark plugs may have fixed your problem. If you are worried about scored pistons, either buy a comperssion tester or take it in for a quick test. (Should be free or very cheap) I suspect that since the motor is running fine, you have no piston damage. If you continue to have the re-start problem, it could be a lot of different things, but fuel delivery would be at the top of my list of things to check out. Since your motor is 20 years old, change out the cheap/easy stuff like the primer bulb, gas line, fuel filter. Run a can of sea foam with the next tank of gas.

-J.
-J.

I used to have a late 70’s Johnson. Had the same problem. It would run fine till it got hot or not restart till cooled off. Pisser worked fine all the time. New thermostat fixed it. The old one wasn’t opening up at temp and the failsafe in the motor would shut it down. Cheap and easy to do. Same thing happened on my new Merc 4 stroke last summer.

Thanks for the advice. I might try the thermostat first and see what happens with that. Is there anyway to tell if the thermostat is shot before putting one in? Other than the motor just not starting after it gets hot. Might be able to just take it out and check it before buying one. Otherwise I guess trial and error until it works right.

Id go with the thermostat first. I have had coils that won’t work when hot, but coils are expensive. try the thermo first.

Waterswat, the thermostat is cheap, probably under $20.00. I know when you get an engine too hot too many times it does scour the piston walls and piston plus the rings loose thier seat, in other words it looses compression making it harder to start. Part of the reason may be because when it starts when its cool is because the oil in the cylinders gets thicker from cooilng off which will raise the compression enough so that it starts. Low compression motors that are worn start harder. Plus if it has points its time to check those too because if they are burnt or ashed that problem plus low compression will make it start hard then eventually not at all. Try the thermostate first then go from there. If you need help after trying a new thermostat message me and i’ll help, those motors are easy to work on. I work on all my old motors and i’ll guide you through it, if you can change a sparkplug you can fix your motor.

Thanks for the encouragement and help mossydan. And everyone else. Called the dealer and asked them about it and they said it is my waterpump, more than likely. He said it will pump water at higher speeds, but it isn’t pumping enough to cool the engine. For a test he told me to take it to the river, start it and just idle. Then touch the water and if it is too hot to touch it is the waterpump. So I need to test it and then go from there. Do all motors, like ones this old have a thermostat? One guy I talked to said he wasn’t sure if they even had a thermostat. Time to do a little research. Thanks again. MD I will keep your offer in mind. Thanks

I don’t know why that ’85 wouldn’t have one. When you find it pull it out and check to see if any small rock or sand is blocking it to keep it from opening up. Then put heat to it to see if it opens.

It probably does have a thermostat. My 15 HP Evinrude (1982 model) had one. You will have to take the head off to get at it but it isn’t too bad of a job. The head gasket will have to be replaced too. With my motor, the thermostat was obviously corroded and wouldn’t move. The motor would run fine for about 10 minutes and then it would start to over heat. Replacing the thermostat solved that problem!

Good luck

Rootski

Well I took it to the river last night and I am going to put a new waterpump in it first. It started fine but I just left it on the trailer and idled it for a while and after about 30 seconds it was just spitting water and not pumping it like normal and then the water got real hot like the dealer said. I talked to Starks Sport Shop in PDC about it and after I change it out we will see. But thanks for the input. Hopefully this will be all it needs. If not the thermostat will be next. Always something. Oh well another excuse to be in the garage, drink beer and listen to the brewers.

Let us know how things turn out.

I’ll let you know. Lucky I have 2 boats this one is just my duck/deer/get out on the water fast, don’t really care what happens boat. Had it since I was 15, but it sure comes in real handy. Let the kids have it one day.

If you need help, I have wrenched on a few motors from 4hp Johnson to 1958 35hp evenrude. I live in LAX…I’d be willing to lend you a hand. (I have my own tools too)