Problem diagnosis help?!

[Vikingbear8]

Hello all I was wondering if I could get some help diagnosing what is wrong with my engine.

Just to get this out of the way I already rebuilt the carb and ran sea foam through the tank 8)

1995 Johnson 15HP

Okay so it is running really groggy. But it seems like the first run of the day everyday it runs like a champ. Then the rest of the day it just drags, i can usually get up to about 22mph and when it bogs down I get about 5.5-6. It also occasionally sputters, every 10-15 minutes I will get a brief jolt of power then straight back down. I noticed today, it seems to run well in reverse, I took a video of it so I hope you can kind of hear how it sounds, that higher winding in reverse is how it sounds when its running smooth, then when I kick it into forward you can hear how it sounds a lot lower and like its struggling. Rebuilding the carb doesn't seem to have done much, it acted the same before and after. I am sure I am forgetting some info but hopefully someone can help. Thanks a lot
https://youtu.be/_naM_XxyRlM
[youtube]https://youtu.be/_naM_XxyRlM[/youtube]

 

[shawnfish]

sounds like a fuel issue. I would have started checking for any leaks at the fuel tank, then the fuel line, primer bulb, connection at the motor,then to the fuel pump and on to the carb before I rebuilt it because you may have not had to rebuild it, did you rebuild it after you noticed the problem or was it rebuilt and running fine and then started acting up ?? did you try pumping the primer bulb while you were motoring? and if so did it run ok while pumping? these may sound like stupid questions but without knowing your level of knowledge on motors I figured id ask...

 

[KMixson]

Check your plug wire routing and condition. Make sure it is not grounding the wire out somewhere. Make sure your shifting linkage is not contacting the plug wire while in forward grounding it out. I had a problem one time with my plug wires grounding out on the block intermittently. When I pulled the cover off it would run fine. Then when I put the cover back on it would intermittently miss on a cylinder again. What was happening is that the cover would move the plug wire just a millimeter too close to the block and ground it out. After rerouting the wire I had no more problems.

 

[Vikingbear8]

Thanks for the suggestions guys, and don't worry about giving supple fix suggestions my engine knowledge is indeed pretty limited.

As for the main fuel line and primer bulb, that's actually a problem I had last year, so they all got replaced. And that's the first thing I played with when this started happening because that's what I thought it was. The bulb stays full and pumping it has no effect on the engine performance. So I don't think its that. I rebuilt the carb after this started happening, because from what I read everyone seems to say try that first, and if I didn't have to oh well, it was only like $30 for the kit haha.

Okay so will the plug wires what all would cause them to ground out, contact with metal I would guess? I will play with that a bit, unless I am completely mistaken on what they are though they are really short, and not much is around them.

I did also try running the engine with only one plug connected as I read that somewhere, and one ran noticeably worse. Is that an indicator of something? I read something about the depth they screw in can cause similar problems but didn't quite understand it.

 

[Tallpine]

Have you replaced the plugs?

 

[crazymanme2]

Sounds like an electrical component is heating up & intermitily shorting out since it always runs good first thing.

 

[Charger25]

Yeah I was going to say fuel as well but I noticed the new bulb and line. I'm going to say that its running just as bad in reverse as forward judging by how far you turned the throttle. If I did that I'd have water coming over the transom.
If you unplugged a plug and it got worse then I'm gonna guess its getting fire to both plugs.
SOooo I'm going back to some kind of fuel restriction. I actually had a new pump ball go bad once. the flapper inside would shut and cause it to bog down, idled just fine but would not run well.

 

[Pappy]

In the video, in forward gear, your engine is running on one cylinder.

The reason you get more RPM out of it in reverse is that, in reverse, the exhaust exiting the prop hub is washed back through the propeller blades thereby venting the propeller and allowing it to slip.
Chances are you have an electrical component heating up and failing. Your first run of the day sort of supports this.
You will have to diagnose this while the engine exhibits the problem. You will need a pair of plug wire pliers that will insulate you from being shocked.
Tie your boat tightly to the dock or leave on the trailer with the engine submerged enough to be run in gear at the RPM the problem occurs. Your choice.
Diagnose only while the problem is occurring.
Be aware that the secondary voltage on this particular engine can be as high as 60Kv which can literally knock you out of the boat.....I do not recommend you doing this with substandard pliers or if you do not know what you are doing.
While the engine is acting up pull either plug wire and see which one is not firing.
Switch plugs cylinder to cylinder to verify it is not a plug.
Switch primary coil wires and secondary (spark plug wire) coil wires to verify it is not a coil. (You are switching #1 coil to #2 cyl. and #2 coil to #1 cyl. )
If either one changes the cylinder that is not firing then you have found the problem. If not, it is an ignition component.
You can then take the engine to a shop and have them check the stator output to the power pack and verify voltage into the pack and check pack output and verify either low or no output.
Or......you can take a chance and replace the pack. Shade tree style of repair but it is your choice.
A second thought here is water entry into a cylinder. You will see evidence of this on a spark plug if this is occurring. Doubt this is happening unless the engine had been severely overheated.

 

[Vikingbear8]

Wow thanks for the detailed explanation. I was hoping it wasn't something electrical because that is well above my skill level and i would imagine expensive. Like i said it did run it one each plug individually, but that was just here at home and one did run noticeably worse than the other one. So if i determine it is one of the cylinders how would I go about fixing that? Again sorry I have pretty limited knowledge here. Closest shop I can find is over an hour away so i didn't really want to go unless I have too, at least now I have some idea of what to tell them may be wrong

 

[richg99]

Put two new properly gapped plugs in. Can't hurt and has saved me grief in the past. I now replace them once a year....just because. Rich

 

[Pappy]

Re-read my post again. It is all there for you.
There is no need to put in a fresh set of plugs.
Only diagnose while the engine exhibits the issue.

 

[Daretofish]

Spark plugs gave me similar symptoms, I had replaced them so I was looking elswhere, but, put some different ones in and have been running pretty good ever since-1980 15hp Johnson