no spark, old mercury 50hp 4cyl

[CatriderF7]

I bought this boat last week from a friend. It had been sitting a few years but after emptying the old gas from the system i got it started up and it ran great. Started multiple times with no issue. But now after sitting a few days it has no spark. I disconnected the big harness at the motor and the small black/yellow wire near the coils and still nothing. At one point it sparked maybe 2 or three times while turning the engine looking at a spark tester but then it stopped again. I'd like to know what the next step is or if someone can tell me How to ohm out the stator and or coils. The engine I believe is a 71 merc 50 4 cyl. Sn is A160671

 

[Laddies]

Re: no spark, old mercury 50hp 4cyl

A160671

 

[CatriderF7]

Re: no spark, old mercury 50hp 4cyl

A160671 would be a late 1985 or pre production 1986 4 cyl 45HP engine not a 71 which would be a ign with 4 coils is that right? It probably says Classic 50 on the cowl.

That sounds about right. It has 4 coils. Doesnt say classic tho it just says mercury up high and 50 on the top of the drive. I saw some pics of similar style engines labeled 1971 online but 85 is a lot more realistic to me. I tried looking up the sn on some parts websites but no results were found. Weird thing is I just tried starting it up and it runs perfect again. Started a good 5 times and it starts immediatelty.

 

[Laddies]

Re: no spark, old mercury 50hp 4cyl

Sounds

 

[CatriderF7]

Re: no spark, old mercury 50hp 4cyl

Alright thank you. We took the boat out an hour ago and drove it around the lake for a good half hour with no issues, weird. Ill check this out tomorrow tho, or maybe I should wait til next time it doesnt start.

 

[CharlieB]

Re: no spark, old mercury 50hp 4cyl

The stator driven ignition has a minimum cranking speed of 300 RPM to generate sufficient voltage for the ignition to fire.

Weak battery, poor dirty battery cables, starter cable, dirty starter commutator, any or a combination of will crank all day too slow to make a spark.

A weak battery can regain some strength after sitting a while and the motor starts again.

Clean everything bright and tight.

Charge the battery the take it and have it load tested.

Chances are there is nothing wrong with your ignition.

 

[CatriderF7]

Re: no spark, old mercury 50hp 4cyl

The stator driven ignition has a minimum cranking speed of 300 RPM to generate sufficient voltage for the ignition to fire.

Weak battery, poor dirty battery cables, starter cable, dirty starter commutator, any or a combination of will crank all day too slow to make a spark.

A weak battery can regain some strength after sitting a while and the motor starts again.

Clean everything bright and tight.

Charge the battery the take it and have it load tested.

Chances are there is nothing wrong with your ignition.

The engine spins plenty fast, I'm not sure on rpm because the tach doesn't work but the batteries a brand new 1100 cranking amp battery off my bayliner. But the boat ran fine a few different Times of starting it the past couple days. And now today I went to go outfishing and the boat wont start. Every once in a while it will pop a few times like its about to start but then it goes dead again. Spark plugs are brand new also

 

[CatriderF7]

Re: no spark, old mercury 50hp 4cyl

And in the time I typed out that reply I went over and turned the key and it instantly started up...

 

[NissanUser18]

Re: no spark, old mercury 50hp 4cyl

Try putting a little bit of gas on each spark plug, or put some drips of gas into the spark plug holes. If that doesn't work, rent/use/buy a current detector it will show you where the electrical current stops.

 

[Faztbullet]

Re: no spark, old mercury 50hp 4cyl

Check the stator as it sounds like its failing ......

 

[CharlieB]

Re: no spark, old mercury 50hp 4cyl

Or the ignition switch is beginning to fail.

The ignition switch is two seperate switches within the same housing. One switch turns 12V on/off to acc, The other switch simply disconnects/disconnects the kill wire to ground to kill the ignition/spark.

The Black wire with yellow trace is the ground to kill from the ignition, the solid Black is ground. With the motor OFF check the B/Y for ground with an Ohm Meter, switch the key on/off a dozen times, if ever any ground with the key ON then the switch is going bad and killing spark.

 

[CatriderF7]

Re: no spark, old mercury 50hp 4cyl

Its getting gas fine everytime I pull the plugs theres gas on em. Im going to check the stator and That switch box. Sucks trying to fix intermittent issues like this

 

[CharlieB]

Re: no spark, old mercury 50hp 4cyl

Intermittent issues can be the tough ones to track down.

But a total 'no spark' most often comes down to a ground on the black/yellow simply killing spark. Which is why I advised testing the ignition switch, I've had times when I had to turn the switch on/off 60 times before I finally saw it short using a meter.

Remember, there is NO RETURN on electrical parts. You have GOT TO prove the fault before ordering parts.

 

[appleo]

Re: no spark, old mercury 50hp 4cyl

Intermittent issues can be the tough ones to track down.

But a total 'no spark' most often comes down to a ground on the black/yellow simply killing spark. Which is why I advised testing the ignition switch, I've had times when I had to turn the switch on/off 60 times before I finally saw it short using a meter.

Remember, there is NO RETURN on electrical parts. You have GOT TO prove the fault before ordering parts.

Can't I just unhook the kill wire from the switchbox...and that will eliminate all possiblibilites for inadvertent killing....then try to start?

 

[bgc]

Re: no spark, old mercury 50hp 4cyl

I bought this boat last week from a friend. It had been sitting a few years but after emptying the old gas from the system i got it started up and it ran great. Started multiple times with no issue. But now after sitting a few days it has no spark. I disconnected the big harness at the motor and the small black/yellow wire near the coils and still nothing. At one point it sparked maybe 2 or three times while turning the engine looking at a spark tester but then it stopped again. I'd like to know what the next step is or if someone can tell me How to ohm out the stator and or coils. The engine I believe is a 71 merc 50 4 cyl. Sn is A160671

At aint an old motor.....its still wet behind the ears....

 

[CharlieB]

Re: no spark, old mercury 50hp 4cyl

Sure, if it then has no spark you have a problem. Bet it does start as long as it cranks above the minimum 300 RPM.

Once it starts, how you going to kill it?