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Seeking assistance with Mercury outboard 25HP, detached from boat

E

ejlion

New member
Hello. I have a lot of experience with small engines, but am a total newbie to boat motors.

I detached my friend's boat motor and took it elsewhere to try to get it running. I'm realizing this may have been a mistake, as this means it doesn't have the wiring harness with the thick pins, throttle, ignition, etc.

With another friend's help, we've cleaned out the engine, filter, have fuel and spark, but can't get the engine to turn over. We're thinking it's because of the ignition, choke, throttle, etc.

I've attached a photo of the harness pins and another with some information about the motor.

I'm hoping someone can tell me...

- is it stupid/hopeless to work on this away from the boat? should I re-attach it before doing anything else?

OR

- is there a way to hotwire/trick this motor into thinking it has ignition/permission to start - either by jumpering something on the harness, or the motor itself?

We DO have "ear muffs"

Any advice would be appreciated. Thank you.

braintoss-2021-08-24-18-41-36-image.jpgbraintoss-2021-08-24-18-49-07-image.jpg
 
It does not need the harness to run, you have spark and fuel so unless it has low compression or some other fuel issue; water, plugged passages in the carb, etc. it will run. You need the harness to start it with the electric start and to shut the engine off with the keyswitch. You will need to choke the engine to shut it off or flip the emergency stop switch on the front side of the engine. Does it have a manual starter on the engine? If so, pull it over... If it only has electric start, jump the starter with cables and a 12 volt battery.
 
fitz73222 said:
It does not need the harness to run, you have spark and fuel so unless it has low compression or some other fuel issue; water, plugged passages in the carb, etc. it will run. You need the harness to start it with the electric start and to shut the engine off with the keyswitch. You will need to choke the engine to shut it off or flip the emergency stop switch on the front side of the engine. Does it have a manual starter on the engine? If so, pull it over... If it only has electric start, jump the starter with cables and a 12 volt battery.
Click to expand...

Hello and thank you!

If I may drag you further into this... :D

The motor is standing against a picnic table. We have cleaned the fuel passages and carb to the best of our ability. We've tried a jump-pack and it successfully jolts/turns the starter, which appears to be properly aligned. We do not have a fuel tank attached, but we believe there's enough starting fluid in the chamber for it to run a bit.

Unfortunately, the engine doesn't turn over or continue running. Our hypothesis was that the lack of ignition was not permitting it to start. If this is how they run, couldn't a boat thief just detach the harness and pull the starter? Don't get me wrong - I believe you, I'm just surprised.

Back to the issue, it appears something else is wrong. Both spark plugs fire if we hold them out and pull the starter. Do you have any suggestions on what to try next?

One note: there is NOT noticeable suction on the fuel line when we pull the starter. Of course, it's going through a filter, so it may just be too small to notice on my fingertip.

Thank you again, and anyone's thoughts are welcome.
 
For a carbureted engine that generates its own ignition energy from it's rotating flywheel will start with the remote harness disconnected. Yes, it's that easy to start one, just wrap a rope around the flywheel and give it a pull and gone...You need to hook up pre-mixed fuel to the engine with a fuel line, fill the carb and pull it over. You will destroy that engine trying to start with starting fluid since it has NO OIL in it.
 
ejlion said:
Hello and thank you!

If I may drag you further into this... :D

The motor is standing against a picnic table. We have cleaned the fuel passages and carb to the best of our ability. We've tried a jump-pack and it successfully jolts/turns the starter, which appears to be properly aligned. We do not have a fuel tank attached, but we believe there's enough starting fluid in the chamber for it to run a bit.

Unfortunately, the engine doesn't turn over or continue running. Our hypothesis was that the lack of ignition was not permitting it to start. If this is how they run, couldn't a boat thief just detach the harness and pull the starter? Don't get me wrong - I believe you, I'm just surprised.

Back to the issue, it appears something else is wrong. Both spark plugs fire if we hold them out and pull the starter. Do you have any suggestions on what to try next?

One note: there is NOT noticeable suction on the fuel line when we pull the starter. Of course, it's going through a filter, so it may just be too small to notice on my fingertip.

Thank you again, and anyone's thoughts are welcome.
Click to expand...
What is your compression? Does spark jump a 7/16" air gap? Is the kill switch on the front of the motor in the run position?
 
Last edited:
fitz73222 said:
For a carbureted engine that generates its own ignition energy from it's rotating flywheel will start with the remote harness disconnected. Yes, it's that easy to start one, just wrap a rope around the flywheel and give it a pull and gone...You need to hook up pre-mixed fuel to the engine with a fuel line, fill the carb and pull it over. You will destroy that engine trying to start with starting fluid since it has NO OIL in it.
Click to expand...

Thank you. It's extremely helpful to know that the motor should run independently of the boat. I will get some fuel into it with oil at, I assume, 50:1.

Again, I'm stunned that more boats don't disappear. What am I missing? Is it because the harness usually connects inside a housing that requires tools to open?
 
flyingscott said:
What is your compression? Does spark jump a 7/16" air gap? Is the kill switch on the front of the motor in the run position?
Click to expand...

I'm sorry, but I'm not sure how to answer your first question. How would I measure or estimate the compression?

As for the spark, I'll see about jumping. I was just holding it against a metal surface as I've done with tractors and such. From your question, it sounds like I need to replace the plugs if that spark is NOT jumping that large a gap.

Thank you.
 
There is usually a red toggle switch on the front off those motors say run/off on it. You use a compression tester to measure compression. Plugs have nothing to do with how far spark jumps. Not to be a jerk but are you sure you should be working on this motor? I think you need to take your motor to a dealer.
 
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