gas cuts out on 2004 bigfoot mercury 25hp outboard.Changed spark plugs helped but?

[Fredfloat]

The boat sits most of the time. I had problems starting it but when I got it started it would only go half speed.Got the old gas out and put new ethanol free 98 oct gas and Seafoam in it. Still half speed but occasionally would go faster for a short time. Later, I changed the spark plugs that had been in it for some time and it immediately ran full speed no problem. I ran it for a mile and stopped to fish for an hour. When I restarted it, it was going ok but then it was as if the gas had been cut off. I restarted and could only get it to half speed. So changing the old spark plugs (see below) had a huge effect but not for long. As it's a major hassle to get a friend to drive way out, put it on a trailer and drive into town and back, plus the cost of the local expensive dealer, I try to do what I can to do whatever possible if it's something a non mechanic like myself can do. Any ideas what might be the culprit? Thanks

 

[Fredfloat]

Just tried it again. Half throttle goes but if I push it to full or much past half it starts to die.

 

[Fredfloat]

Sorry can't figure how to edit my earlier post. I'd add the primer bulb remains quite firm after I run it and start experiencing problems. I can squeeze it a little (like 10%)but not much.

 

[racerone]

Run with a timing light hooked up and monitor spark.-----Sounds like it has weak spark and runs on one cylinder.

 

[Fredfloat]

Run with a timing light hooked up and monitor spark.-----Sounds like it has weak spark and runs on one cylinder.

Thanks for the reply. Don't have that thing but I'll look into it. These are the old spark plugs. I'll take out the new ones that only ran well once and send photo. So if it has a weak spark what would be the next step?

 

[racerone]

You have to do some testing,----Perhaps learn to make a spark tester with some scrap wire.----Does spark jump a gap of 3/8" , yes or no ?

 

[Fredfloat]

You have to do some testing,----Perhaps learn to make a spark tester with some scrap wire.----Does spark jump a gap of 3/8" , yes or no ?

I have 2 new spark plugs. If I take out the ones I just put in and put these new ones in and the boat runs full power for half an hour or so but starts to go half power after stopping for a while does that say anything on what the remedy might be? I'm going to look at plugs I take out and see if they are moist and/or dirty after only running an hour.

 

[racerone]

Trouble shooting needs to be done !----Guessing and changing plugs won't fix the problem.

 

[Fredfloat]

Trouble shooting needs to be done !----Guessing and changing plugs won't fix the problem.

OK. I bought a spark tester and made a video of what happened. https://youtu.be/jU-E5je6Vx4 I put it in between both plugs and the motor would start and a red light could be seen flickering . I should have left the camera on longer and it was a little brighter than I would have liked to see the light but I slowed it down on the video to see better. I've attached what was on the package. Then I took it out, as seen on the video, and tried to show how if I kind of feathered the throttle it would pick up some speed but if I pushed it to full or even 3/4 it would start to die. Any theories on what's happening? It seems like if it gets too much gas it can't handle it. Thanks

 

[Sea Rider]

Seeing a spark through the traslucent bulb doesn't say much, one scenario is when any motor runs at idle with no load, other scenario when that same motor runs at speed with a load. Will need to troubleshoot all the electricals with appropriate instrumentation or the wild guessing will continue forever..

Being a 14 year oldie could have already a faulty electrical component heating up when on demand and missing as stated till cools down to start the whole endless process again. Those sympthoms are a nightmare to troubleshoot fast..

Happy Boating

 

[Fredfloat]

Seeing a spark through the traslucent bulb doesn't say much, one scenario is when any motor runs at idle with no load, other scenario when that same motor runs at speed with a load. Will need to troubleshoot all the electricals with appropriate instrumentation or the wild guessing will continue forever..

Being a 14 year oldie could have already a faulty electrical component heating up when on demand and missing as stated till cools down to start the whole endless process again. Those sympthoms are a nightmare to troubleshoot fast..

Happy Boating

It's old but actually few hours used.It has sat in the water in a dock slip. Today I bought a new fuel filter and will try that before getting ready to take it to $ervice.

 

[Fredfloat]

BTW it starts cutting out right away if pushed to full throttle so I wonder about things getting warm being the problem? Just called dealer and they want to just leave the boat for a week and get to it when they can plus charge a lot so I'll continue to see if I can figure out more about this.Any further tips appreciated.

 

[QBhoy]

I’m suspecting you may be running off the battery alone maybe ? As in the engine is not producing a charge or its own power ? Meaning the battery is being drained to produce the spark making it not sustainable ? How is the battery ? Has it been starting the motor all this time without needing to recharge it ? If so, perhaps I’m wrong ? Just sounds like it otherwise. If what I’m saying is ringing true, put a meter on the battery when the motor is running at greater than a fast idle. See if she is producing.

 

[Fredfloat]

I’m suspecting you may be running off the battery alone maybe ? As in the engine is not producing a charge or its own power ? Meaning the battery is being drained to produce the spark making it not sustainable ? How is the battery ? Has it been starting the motor all this time without needing to recharge it ? If so, perhaps I’m wrong ? Just sounds like it otherwise. If what I’m saying is ringing true, put a meter on the battery when the motor is running at greater than a fast idle. See if she is producing.

Appreciate the comment. I think the battery is charging as I see it on the fishfinder and it gets up around 14 volts as I'm moving. It's been kind of an amazing battery. I forget how old but pretty old. Still,would usually start the motor even if not used for many months in winter. I did hook up a charger to it some weeks ago as there was beginning to be a problem starting. Since then (and after changing the spark plugs) it starts right up.

 

[QBhoy]

Fair play. Worth me checking. Maybe look at the coils then. Or it may well be an overheating thing.

 

[Fredfloat]

Put the new fuel filter on and took it out. Exactly the same. Starts cutting out after pushing throttle over half. Today I ran it 1/2 mile at that speed and 2 or 3 times got a small backfire. When I got back to the dock I found a surprise. Not so long ago I put 5 gallons of the expensive 98 octane non ethanol in so I didn't think to look at the plastic tank in the back. Yesterday, I added another can of Seafoam. Today I looked at the tank and it looked nearly empty. I hope someone hasn't been stealing gas. Couldn't imagine using that much when I've gone maybe a total of 4-6 miles. (have to look at a locking gas tank cap!). One thing I'll say is the bulb remained pretty firm as I've doing test runs. Anyway got some more of that 98 octane gas and keeping my fingers crossed there's a connection to the cutting out.

 

[racerone]

I do not believe the battery is involved in making spark on this motor.

 

[Fredfloat]

Filled it up with that High Octane gas and a can of Seafoam but unfortunately no difference. The tank was really low before thst. Ran it about 15 minutes. It would go 1/3 to half speed. Had 2 pretty quiet backfires. I could get it to pick a little if I moved the throttle to higher and then back but it wouldn't sustain.

 

[racerone]

Sounds like it might be running on one cylinder.----So does spark jump a gap of 3/8" on both leads , yes or no ?

 

[Fredfloat]

Sounds like it might be running on one cylinder.----So does spark jump a gap of 3/8" on both leads , yes or no ?

So is the way to do that to hold the plug in wire for the spark plug a little bit away?