Boat motor investigation...UPDATE

David Robinson

David Robinson

Well-known member
Guys,
I'm dealing with my 1991 Johnson 25hp 2-stroke outboard being cranky (no pun intended:). Last summer I fixed the starter motor so now it turns over just fine. The new problem to address is its sensitivity to temperature changes. In the summer time when it's hot, she'll start on the second crank. Or when the engine is warm, she'll start instantly when I turn the key. But when it's cold in late November, I can crank on the starter all day and it won't start. I was forced to use starter fluid (I know it's the kiss of death) but I had to pick up my buddy in the layout boat. I'm not taking this boat out until I fix this problem. So, what would cause an outboard to behave like this? I'm just hoping for a lead to investigate before shelling out the big bucks at the marina. Thanks.
 
Last edited:
Dave,
The first thing that comes to mind for me is to make sure you have winter gas in the tank. In Mich just like here the gas stations/ suppliers change the formulas several times a year. Winter gas basicly will evaporate at a lower temp which will make starting easier. The reverse is true- Summer gas will vaporize in the system (vapor lock). All the other factors are being tested in cold waether too such as ignition and compression. The good news is that the ignition system on yours is a fairly good one. Good luck.
 
I recommend getting the full service manual for the engine..............I got one for my 2000 40hp Mercury, and it's awesome. It tells you everything. Even tells you "theory of operation", which is often very useful for figuring out how these more complex (i.e. more electronic) engines work. Although, your motor might be more simple.
Troubleshoot charts are also good for diagnosis.
I agree, start with the easy/simple things first........fresh gas, check plug(s), check/clean carb jet, etc. Closely look-over everything, etc.
Good luck!
 
Tom and Brent,

You've both made good points. Thanks for responding.

I have in new gas in the tank and have been reading the manual (love that book) yet I'm still stumped. I've done all the simple things: new spark plugs, Sea Foam in the gas, change the lower unit oil, check the battery, visually inspect everything about a million times.... Just trying to get an idea of what else to check. My current hunch is the carburator.

If you've got any input on cold weather tuning, I'm all ears.
 
Does it have a man overboard kill switch? The one with a little red button held open with a key, attached to a lanyard that you clip to yourself? I have had two OMC 20 & 25 hp motors about the same vintage, same problem, work today, not tomorrow, change the kill switch and good to go. Hopefully it's not the power pack, another favorite in that model and vintage motor. Otherwise, make sure you get good pressure in the hose, then give it several good primer pumps in the cold weather, you should be able to hear it pushing fuel to the carb. If it gets gas and won't start my money says it's the kill switch or the PP.
 
SJ,

I'll definitely check into the kill switch. It's kind of like making sure the computer is plugged in before calling the Geek Squad, hehehe. As for the power pack??? I guess I'll be reading the manual tomorrow. Thanks.
 
I wish I was more familiar with your particular motor........I'm kinda an expert now, with mine, from reading the manual quite a bit.
The carb is definitely a possible culprit.......like the old school of thought: "it's either spark or fuel". The carb has to mix the fuel and air in such a precise ratio, or you won't get combustion.
With 2-strokes, the spark is a little more complex than a 4-stroke spark; it may not be as simple as checking for spark at the plug while you crank it.
I had a really tricky problem with my 40hp, where a ring terminal of a ground wire for one of the electonic "boxes" snapped off, and the box was not grounded and not functioning properly, and the motor would run rough at any rpm over 2000. I think the box was either the rev limiter or voltage regulator...........nasty little problem...I'm still surprised I saw that dangling black wire.
 
It sounds more like a carb issue. If it has been set up to run best in the summer then you go out and use it in the dead of winter the fuel mix will be off. I will only tune up my winter motors when the weather is consistant with colder conditions.
 
Just to clarify, the motor in question has a primer, not a choke, correct? I don't believe OMC made the 20-25-30 series with a choke during that time period, but if it does in fact have a choke, perhaps that could be a problem. I am still inclined, however, to think it is an electrical problem having had exactly the same experience with two motors of the same series and vintage, the fix for which was the kill switch. Have had the power packs die on older motors as well, but usually the failure starts as rpm surging, then at some point, it won't ever start again. Hope this helps, good luck.
 
David, Once the motor starts in cold weather does it warm up and run correctly? The point re: the choke is correct,a primer could be missbehaving. I will check but I think your primer is electric.??? More later.
OOPs , my bad. Your primer is a manual one so just check to see if it is spraying fuel when you pump it. I still think it may be the seasonal blend of fuel. Good Luck.
 
Last edited:
David, this year Johnson is notorious for the kill swith wiring to chaff and short out. My motor was doing this and would start with no problem when it was warm but when you had to crank it in cold weather the wiring would arc out and you could not start the motor, same as if you had pulled off the kill switch lanyard. Try disconnecting the wiring harness for the kill switch and if that is the problem the motor will start. I also had a problem in cold weather when I had an inline fuel filter just prior to the motor, in extreme cold the ice crystal build up in the line at the filter would not allow fuel through. Tapped it a couple of times and it would start. Replaced the fuel filter several times and that problem was solved.
 
SJ and Bob,

Your stories sound a lot like my problem. When the engine is warm, she'll start right up. But if she's cold, I have to crank on it forever. I'll definitely be looking into the kill switch theory on Friday. At least it might be a cheap fix.

As for the choke/primer question...it's an electric start so I just push in the key to prime the carb. There is a "cold start" arm that I can move up to rev the engine when it's in neutral. It will manipulate the butterfly valve on the carburator. I'm not sure if I just muddied the waters or not but I'm still learning. I'll let you guys know how this investigation turns out. Thanks guys.

Someone else said it: B.O.A.T. = Bring Out Another Thousand $$$ Soooooooooo true.
 
My 40hp Merc has an electric choke from pushing key IN, too......it energizes a small solenoid which adds additional fuel directly. The "cold start arm" doesn't sound like anything but another way to open the throttle, which may not be "choking". Choking is when you increase the Fuel-to-air ratio, which helps starting cold engines......and many times choking is accomplished by actually restricting the air intake (similar to closing the throttle).
My solenoid also has a small button on the bottom, so you can push it if the electrical aspect of the solenoid isn't working. You're manually opening the solenoid-operated fuel valve that way. Those Merc engineers sure did put a decent amount of thought into this motor.
 
I solved a poor starting problem I had by draining all the gas that had sea foam in it and replaced it with gas that I added a fuel stabalizier to and the motor fierd and ran just fine, sea foam is a good tool for cleaning the system and decarboning it but can reduce its flash point.
 
David - I have an 8 hp yamaha which was a pain to start in cold weather. A mechanic enlarged the hole in the choke (butterfly ?) and it has been easy ever since. The other suggestion for cold weather is to run it a little with fuel disconnected at the end of a trip. You don't have to run it dry but get most of the fuel run out. Then when you need to restart in cold weather, you give the bulb a couple of pumps and shoot some gas into the engine. I am not sure why this helps but it really works well.

sarge
 
This past Sunday was warm and sunny so I worked on my boat. The first thing I did was to dump all the old gas out and clean the tank. After I filled the tank with fresh gas and added some Stabil Marine, I hooked it up and started cranking and priming the motor. It took about a minute of trial and error but she fired up! Plenty of 2 stroke smoke and coughing but she purred like a cat after a few minutes. Go figure? I guess I can't fix it if it's not broke, hahaha. I'll see this summer....

Guys, thanks for all of your help. If she gives me any grief, I'll start trouble-shooting the list.
 
You must log in or register to reply here.
Back
Top