Mariner eight, intermittent spark

Ok guys so I just picked up this early 90's? Model mariner eight. It is a 2 stroke 2 cylinder. Guy has had it sitting in his shed for several years.

To begin with I thought I was having fuel problems. the engine would run for 10 seconds or so but only after i pulled it 18 times... so I took the carb apart, cleaned everything, twice just to make sure and put it back together. Motor still wouldn't stay running. That carb is clean. Spark plug were getting wet.

Then I checked the spark. No spark. Oh wait, there it is! Nice an blue and pretty, oh wait and no more spark...

Any pointers on what could be the cause of an intermittent spark?

I tried to add a picture of the engine but it says its too big. Engine looks nearly showroom. It is in excellent shape cosmetically.

Update just in case someone is searching on the same issue.


I think I've narrowed the issue down to the switch box. I can bypass it and get good spark out of a coil. Also my dad called the local boat shop and the guy says that's a common issue. He's sold 16 of that exact part number in the last 2 years.

So, I'm pretty confident that is what it is. I'll update again once I get the new one bought and installed.

Switchbox seems to be the most common problem with Mercury/Mariners when it's a spark issue. I just replaced one on a friends 15hp this past spring.

Yep. I've got a new one ordered and should be here tomorrow. I'll install it no later than Friday and report back.

So I got the new switch box installed and the spark was great! For a little bit. Then nothing.

Checked the resistance across the trigger and according to this site
https://www.outboardignition.com/page39.asp
It was way out of spec. So I'm guessing it it bad. It may have not been the switch box, it may have been the trigger the whole time.

My wife came outside after she noticed I didn't have it running and asked " what's going on?"
I told her " the part I bought didn't fix it" and I kept tinkering.
And after a minute or two of watching me she said " do you know what's wrong?"
All I could do was look at her, smile and say " nope." Then we both enjoyed a good laugh. It was great.

She's been hounding me about remodeling the bathrooms and is about to cut the budget.

I like her already, and that's what wives are for.

Are you checking spark on both coils? If no spark on either of them check to make sure it's not your kill switch that has failed or is intermittent. Generally you can just disconnect the ground from it to diagnose it and eliminate it as a problem. If it's not a coil and it's not a kill switch, it could be a bad stator OR powerpack, but I ain't smart enough to diagnose how to figure either of those out. I generally just throw on a new powerpack. I have found that throwing parts at motors is still cheaper than paying a real mechanic :lol:

Tallpine said:

I like her already, and that's what wives are for.

Click to expand...

Exactly haha. I might be able to squeeze her for $50 but that's gonna be about it. And really, we NEED to do the bathrooms. Ya know, when youre broke, it comes down to being responsible, keeping a stable budget, making sure the family is taken care of, and all that jazz. She keeps me in check, usually haha.

Jim311 said:

Are you checking spark on both coils? If no spark on either of them check to make sure it's not your kill switch that has failed or is intermittent. Generally you can just disconnect the ground from it to diagnose it and eliminate it as a problem. If it's not a coil and it's not a kill switch, it could be a bad stator OR powerpack, but I ain't smart enough to diagnose how to figure either of those out. I generally just throw on a new powerpack. I have found that throwing parts at motors is still cheaper than paying a real mechanic :lol:

Click to expand...

I disconnected the black/yellow stripe wires, which suppesedly go to the kill switch. And no change on either coil. Coils passed an ohm check. I was told they need to be +/-10% of 1k and the both were 930-970 IIRC... And is a power pack the same as a switch box?

Also
Never worked on an outboard before so I'm learning as I go. I have done work on motorcycles, Atv's, cars and trucks,and lawn mowers and other junk so I feel like I have a decent start. But like with anything you've never done before, there's a learning curve.

Sorry not too familiar with your particular motor to know if it has CDI ignition or not. But most of the motors I have used have an electronic "power pack" that basically controls ignition. If it fails it can cause all kinds of crazy crap to happen, but so can a bad stator. Check for loose/worn wires grounding out from the stator and coils, inspect all the grounds to the coils and ignition parts too.

Ok. Update

So it turned out to be a combination of a few different things.

The original power pack was bad, and so was the trigger, but what was really killing me was the stop button on the end tiller handle. It kept shorting out. But before the power pack and trigger were replaced, it still wouldn't fire even with all kill switches bypassed.