# Johnson 25HP issue



## jonmac3569

I have a 1975 Johnson 25 HP. It did not run when I inherited it. It had been setting up for 10 years. I changed the lower unit oil, plugs, starter pull rope, rebuilt the carb and changed the impeller.

It idles very well now and runs well at lower speeds. If I try to open it up, it will start "choking" and seems that it is not getting enough gas. Initially I was using one of the replacement fuel lines with the priming bulb built in. I changed back to the original hose and it ran a little better. But at higher speeds I still need to reach back and pump the bulb as I am going down the river to keep it running.

Obviously sounds like it is not getting enough fuel. Any ideas why?

Thanks


----------



## crazymanme2

Fuel pump bad #-o


----------



## baseball_guy_99

Agree with crazy. Get yourself a fuel pump rebuild kit.


----------



## Captain Ahab

It is not the fuel pump - on that engine they either work or they do not - since it runs it works

you have a bad connection on your fuel line

Try a new line or new connections and you will be just fine. i have the exact same problem on my 25 hp Evinrude


----------



## jonmac3569

The fuel line that goes from the exterior hose connection to the fuel pump I did not change. I changed the one that goes from the fuel pump to the carb. It is possible it is slightly smaller in diameter than the original. The original was old an dry rotted and appeared to have stretched so it was hard to match the size. Guess also possible the line to the fuel pump has an issue.

I guess I will try replacing the that line and cleaning the pump first. I guess if that does not work I can always rebuild the pump.


----------



## jonmac3569

I changed out that fuel line and it was dry rotted. I could break it just by bending it so maybe air was getting in. 

Does anyone know if they make a rebuild kit for this particular fuel pump on this motor? I checked several sites and found many rebuild kits but I haven't found one that says it will fit this particular motor.


----------



## Pappy

There are kits available for most of the OMC pumps. Some pumps do not have a dedicated kit available, however all the necessary parts/pieces are available with other kits. If you have a dealer available close to you take the pump in and have them match it up to either one of the square pump kits or the other shape.


----------



## jonmac3569

Thanks for the reply on the pump, I will try that.

Got another issue now. I replaced the other fuel hose and all the connections and took it out for a try. It was basically doing the same thing. One time it died, tried to recrank and I got nothing. I looked in the water behind the motor and there was oil dripping in the water. 

See the pics below. There was black oil coming out of the ports in the lower unit and the all the areas the water is pumped through. The oil was pretty black, I had just changed the lower unit oil a month or so ago. Why would it be that black already? Also, is this a broken seal in the lower unit?


----------



## jasper60103

The good news is you don't have a lower unit leak. That's a drain hole in the lower unit. Perfectly normal to see some unburned fuel drain out like that. But it sounds like you're dumping a lot of fuel. Unfortunately, I don't know why. Maybe it needs a long run at WOT since it setup so long?? What fuel ratio are you running? Hopefully, some of the pros will chime in.


----------



## lckstckn2smknbrls

You should try running fuel with a lot of Sea Foam in it to remove the carbon build up. Search "Decarbing".


----------



## jonmac3569

jasper60103 said:


> What fuel ratio are you running?




50:1


----------



## jonmac3569

lckstckn2smknbrls said:


> You should try running fuel with a lot of Sea Foam in it to remove the carbon build up. Search "Decarbing".



Thanks, I will check that out


----------



## jonmac3569

I ordered a rebuild kit for my fuel pump, rebuilt it and took it out today to try it out. It is doing the same thing. Runs fine at idle and lower speeds but when I give it more gas it will choke unless I pump the primer bulb. I got a couple different answers when I originally posted this. Some seem to think that it is the fuel pump, others said that the fuel pump "either works or doesn't". I also checked all connections and replaced all the fuel lines. I had a friend that rebuilt his with the same issue, didnt work, then replaced the pump and it worked great. (different motor and pump)

Can anyone shed some more light on this? Just want to make sure before I spend $80 on a new fuel pump. My pump is in the pic below (before the rebuild).


----------



## Pappy

The pump either works or it doesn't is an accurate description! The fact that you can pump the primer bulb and make the engine run is indicative of a "bad" fuel pump. You are taking the place of or eliminating the fuel pump when you are pumping the primer bulb. The sole purpose of either the primer bulb or the fuel pump is to keep the fuel bowl full and the needle and seat in the carb closed.
Am betting you haven't checked the pulse line and fitting that supplies and powers the fuel pump. Check and make sure the line has no cracks or pinholes. Check the fitting and make sure the port is not clogged or closed. Lastly, there is myriad of ways to assemble that pump incorrectly........you have probably figured that out by now. Any way but the absolute correct way will give you the same issue. There are small umbrella valves in that pump that must be there as well. Have been through several that at least one was missing from. You can remove the supply line from the carb once you have primed and started the engine and take a look at the fuel flow if you want to verify operation.


----------



## Canoeman

Before you sink anymore money into this go over to https://forums.iboats.com/forum.php , register and go to the Johnson section, Make your post thorough and informative, serial number, make and model and explain what is going on in detail and what you have done to try to remedy it... someone over there will help you out.

let us know what you find out..

that is if pappy's advice doesnt work out..


----------



## jonmac3569

Pappy said:


> Am betting you haven't checked the pulse line and fitting that supplies and powers the fuel pump. Check and make sure the line has no cracks or pinholes. Check the fitting and make sure the port is not clogged or closed. Lastly, there is myriad of ways to assemble that pump incorrectly........you have probably figured that out by now. Any way but the absolute correct way will give you the same issue. There are small umbrella valves in that pump that must be there as well. Have been through several that at least one was missing from. You can remove the supply line from the carb once you have primed and started the engine and take a look at the fuel flow if you want to verify operation.



I did take the pulse line off and checked the fittings to make sure, they looked to be not clogged up as far as I could tell, although one is very small. I did not replace that line though. All the fuel lines I took off were so dry-rotted that I could break them by just bending them so I will replace that line too, just in case.

I was pretty careful putting the pump back together but it is definately possible something isn't exactly right. I'm farily confident that all the gaskets, etc are in the right place, maybe not the valves you are talking about. I think I saw at least a couple in there but wouldn't have noticed if one was missing.


----------



## jonmac3569

A little more info:

I took the pulse line off, it appears to be in good shape. The large fitting behind the carb appeared to be open and had some fuel in it, the small fitting above the fuel pump appeared to be open (very small) and appeared to be dry.

I also noticed something on the carb. The gasket between the bowl and the top part of the carb was "moist". Looks like fuel could be seeping through. I have seen where some people have complained about using the "non OMC" rebuild kit and having to do it over, I was very careful to get the seal on correctly and the seal looks to be in the correct place all the way around. Is it normal for this seal to be moist or could this be part of my problem? Or just another problem?


----------



## Firescooby

Free bump for you. I've got a 1972 25 hp Johnson that I'm gonna be working on over the winter, keeping a close eye on this thread.


----------



## jonmac3569

Firescooby said:


> Free bump for you. I've got a 1972 25 hp Johnson that I'm gonna be working on over the winter, keeping a close eye on this thread.



Cool, If you haven't done it yet I would recommend going on ebay or somewhere and buying the *service* manual for your motor. They are worth their weight in gold.


----------



## Pappy

Run the engine again after pumping up the primer bulb and visually check the pump output flow. You may have to do this at higher RPMs to really check it and you wont have much time before the bowl runs out of fuel. At least verify operation at idle.


----------



## jonmac3569

Pappy said:


> Run the engine again after pumping up the primer bulb and visually check the pump output flow. You may have to do this at higher RPMs to really check it and you wont have much time before the bowl runs out of fuel. At least verify operation at idle.



Thanks, I'll try that


----------



## jonmac3569

Well I just put on a brand new OMC fuel pump. I put it on and took it out to try out. Exact same thing! No difference whatsoever. Any ideas?


----------



## crazymanme2

These are some pics of an exploded view of your fuel pump. :lol:


----------



## jonmac3569

Thanks but I replaced it with an out of the box, already put together, pump. The frist time I rebuilt it, but today I replaced it with a new one.


----------



## jonmac3569

I am a little worried about the gasket being wet on the carb. Maybe air and fuel are seeping out there. I initially used a non-omc rebuild kit so I ordered an OMC kit and I am going to rebuild the carb again and check the jets and valves again just to make sure. Hopefully that will fix the issue.


----------



## mmf

sounds like you might be running on one cylinder. Run motor at idle in a barrel and pull one plug at a time to see if it makes a difference. You have a lot of unburned fuel coming out, this is usually found when there is a bad coil or other ignition problem making a cylinder NOT fire.


----------



## jonmac3569

Thanks, I'll try that!


----------



## Canoeman

You can also check to see if they are both firing by hooking up an inductive timing light one at a time.. while running the light will flash.. if you have a dead spot the light will go black etc..


----------



## jonmac3569

Great news, today I finally had a chance to take it out. I recently took the carb back apart and cleaned all the jets, etc. i also rebuilt it with an OMC kit this time. Not sure which was the problem (or both) but it runs great now. Thanks for the help.


----------



## jonmac3569

Took the motor out the other day and it was acting funny. Ran great the previous time I took it out. I adjusted the cam follower since then because the throttle was not opening at the correct point. (per the serivce manual) I apparently did not adjust it correctly, I took it out again and although motor was running well, I could not get past a low throttle setting. I could phyiscally move the throttle to the "fast position" but not getting much out of it. I re-adujusted the cam follower on the fly. After that I could open the throttle up and it seemed pretty normal. Only thing I did notice is that if i opened the throttle up to WOT it would "slip" or sounded like it was kicking out of gear. I am pretty sure that i still need to get the cam follower adjusted correctly but does anyone know why it is kicking out of gear at WOT?


----------



## cajuncook1

Unfortunately, it may a good possibility that you have a worn clutch dog and or forward gear. Not cheap. I hope I am wrong.


Part numbers 31 (clutch dog) and 33 (forward gear)








Another possibility, you may have gotten some trash in your high speed jet causing lean condition. 


Another possibility, you may have a coil going bad that is intermittently missing (not firing). Check the coils for apparently cracking. Bad coils can start missing when the engine warm ups.


I would check the coils first. It is your cheapest and easiest option at this point.

Here is a You Tube link on how to check your coils with *multimeter.* Can get a multimeter cheap at radio shack or similar store. They show how to test an OMC coil.

https://www.youtube.com/watch?v=KT8rk5QWgS0


----------



## cajuncook1

If your clutch dog is worn, then you maybe able to flip the clutch dog around. The teeth on that end infrequently com in contact with the reverse gear, so are usually not worn on that side. Most usually don't use the reverse gear much and certainly not at high speeds.

I would still investigate your coils to make very sure.


----------



## jonmac3569

Thanks for the posts. It is also fouling plugs. I pulled them earlier and that is the 2nd set it has fouled in a short time period. I will check the coils. I was planning on taking it out tomorrow, is it going to hurt anything to run it more? Would probably only be for a short time since I will be going up river to hunt a short distance, could always float back down with trolling motor.


----------



## jonmac3569

Checked the coils (based on the video) they are both good. I am guessing you are right about the gear or clutch dog. It felt like a transmission slipping or something like that, not a loss of power, the motor was still "revving up" but the prop was not turning.


----------



## cajuncook1

If your plugs are fouling up then there are couple of reasons:

- Too rich of a low speed setting

- If you are doing a lot of low speed trolling with your motor and you don't have the proper spark plugs. If you are going to do a lot low speed trolling for extended periods of time then you will need hotter plugs.

- You are intermittently or consistently running on one cylinder and thus the build up of oil/carbon on the plugs 

- If your thermostat is not functioning properly or you have no thermostat. Thermostat usually fault in the open position, but not always.

If you have no thermostat (or faulty) to maintain a powerhead running temp between 130 to 160, then the cold waters that you are running your motor in will accelerate the carbon/coking build up process in your powerhead, on top of your cylinders and around the rings. Your plugs will foul up in no time causing the problems that you are having now.

The thermostat stays closed until the temperature of the powerhead starts reaching about 130 to140F, then the thermostats starts to open to allow some water in to circulate around the water jackets to cool off the power head to maintain a good operation, again between 130 to 160F. So, the thermostat will open and close to help maintain operation temperature. It is within the 130 to 160F range that the optimal combustion of the fuel oil mix takes place.

If you have no thermostat in or it is faulty then water will circulate around the water jackets all the time and the powerhead will stay much colder. Colder powerhead temperatures will allow the unburned fuel oil mix to build up and slug up all over instead of being burned off or exiting the exhaust/water mix going out near the foot of the motor.

Things to do

1. check your thermostat
2. gap your Champion J6C plugs to 0.030 (hotter and better plug for trolling)


If your plugs are fouling, then they can't spark properly and may create poor running conditions.


Some things to think about.


***Another thing that came to mind, if your motor is revving at higher speeds, but the propeller is not turning, then your prop hub may be slipping. (The prop hub is harden rubber material in the propeller that allows the prop to spin but if it hits something hard, then it will break and slip to protect the gearcase and drivshaft and motor from damage.

Read this link, it will tell you how to diagnosis a spun hub.

https://www.tinboats.net/forum/viewtopic.php?f=4&t=13786


----------



## jonmac3569

Thanks for the info. I will try that.

Took it out today and it ran pretty good other than doing the same thing. Ran good up to WOT then motor would rev up and at the same time prop would stop spinning or slip out of gear? Not sure which but I have some stuff I can try now. 

At least I have until spring to get it figured out.


----------



## jonmac3569

Checked the thermosat, definatley failed in the open position so that explains one of the issues.


----------



## jonmac3569

I am changing out my thermostat today. The old one was failed open. I found this rubber plug (see pic) in the hole that was just beneath it. It was not in one of the bolt holes, there are 3 of those. it does not say anything about it in the service manual and does not show it in the parts list. Is this supposed to be here? what is the purpose?


----------



## jonmac3569

Here's a better pic of the plug that was in there. It appears to be manufactured, not something that melted in there. It has a taper on the bottom and a ring around the top which doesnt match the tube I pulled it from. It fits snug in there but the taper doesnt reach the bottom of the port. (scratches along the top are from me prying it out) Is this something that may have been added to change the performance in some way? run hotter? etc


----------



## crazymanme2

Looks like some sort of water by pass restrictor :?:


----------



## jonmac3569

crazymanme2 said:


> Looks like some sort of water by pass restrictor :?:



That's interesting. I know some cars use those, what would that do in this motor? Would it restrict the flow of the water and make it run hotter?


----------



## lckstckn2smknbrls

You should ask on www.Iboats.com in the evinrude johnson forum.


----------



## crazymanme2

> That's interesting. I know some cars use those, what would that do in this motor? Would it restrict the flow of the water and make it run hotter?



I believe its when your thermostat is closed it permits water to flow for the tell tale :?:


----------



## jonmac3569

Thanks for the reply. I took it out today and I still have the tell tale and it is running fine. It's not in the parts lists or service manual so I am going to leave it out.


----------



## jonmac3569

Makes me wonder if someone could have "failed" that thermostat on purpose, then blocked the bypass valve in order to make the motor run cooler. That way all of the water would flow through the thermostat.

Don't know why they would do that becuase it was causing a lot of carbon build up in the motor and I was fouling plugs left and right.


----------



## cajuncook1

If your your water pump system is functioning properly then water should come out of all the time. The thermostat opens up at a certain temperature about 140 to 145 degree F on your motor. This completes the water circulation path through the water jacket pathways around the cylinders. If the engine temperature is lower then the thermostat stay close and water still circulates but not around the water jacket cylinders, so the motor temp can warm up. So water should always becoming out of the tell tail or the exhaust relief hole.

Here is a diagram of a 1973 25hp Johnson water flow pathway and cooling. Should help you to understand. 

The piece of junk you found in the thermostat hole is odd. Maybe the person that service the motor prior to you investigating the thermostat was a bit sloppy and accident drop that in there. I dunno!!










Oh, just wanted to let you know, you motor does not have water re-stricters. Larger hp motors that had 3 or more inline cylinders would.


----------



## jonmac3569

Thanks, yeah looks like they were blocking off the bypass line for some reason. Strange


----------



## cajuncook1

jonmac3569 said:


> Thanks, yeah looks like they were blocking off the bypass line for some reason. Strange




Did you ever find out what was causing your lower unit kick out of gear or was it a spun hub on your prop???


----------



## jonmac3569

Did you ever find out what was causing your lower unit kick out of gear or was it a spun hub on your prop???[/quote]


Yep, actually yesterday I tried putting the mark with a waterproof pen on both the hub and prop and sure enough it was spun after my last run. Glad it was that and not a gear issue! Thanks for that link!


----------



## cajuncook1

Cool 8) , glad to hear there is a happy ending to this story!!!


----------



## jonmac3569

Put a new prop on and took it out today. Ran great! hopefully no more issues for a while!


----------

