50hp 3 cyl running fine until electrical check

[ronsealdeath]

Hi there,

I have a 50hp Merc 3 cylinder, not sure of year but serial number is hard to read as its been stained by something but looks like 3 numbers maybe 144? then 613246.

I uncovered the engine from winter today and ran her up fine, idled her away for 15 mins whilst I checked charging circuits and other bits and bobs. As I am wiring up a tach soon I used my Multimeter to check which of the wires from the tach harness at the control box, was the hot wire giving +12v. I had the -ve wire of the multimeter on the battery -ve and the +ve red wire/probe checking the tach harness connections. Now something bad must have come of this because when I touched the multimeter probe to one connection, the engine coughed and the revs died a bit, it idled for about 2 seconds more then died. So I figured something must have come of my electrical checks!

I tried starting the engine again and would get a cough if I gave it loads of warm up lever, a puff od smoke and then nothing. It now wont start for love nor money. I'm getting loads of fuel by the looks and it feels like I am now not getting spark.

I can't do a spark test for a couple of weeks now due to work and the fact its raining here again this afternoon. I'm going to order some new plugs and try that but does anyone have an idea what I may have done? The fuse on the engine is fine, ignition cut off switch is ON, its getting fuel (plugs are soaked and exhaust has fuel coming out with the water), its cranking fine etc....

What might I have done? Could I have nuked the powerpack or something?

Please not this engine is new to me and has not been fully tested for compression etc... I'll do this next time. Also I have disconnected the Autoblend system and used 50:1 premix. I had a thought this may be fouling the plugs at idle but having cleaned the plugs and tried re-starting its still not firing. I wondered if the autoblend gives a higher fuel to oil ratio at idle which means when removed the plugs may get fouled?

Any ideas on what could be the problem? ANy help would be gratefully received!

Cheers
Al

PS It has surface gap plugs so I think its an 1986 to 1990 model?

 

[Faztbullet]

Re: 50hp 3 cyl running fine until electrical check

The only thing wiring the tach could have done was to pop rectifier..

 

[CharlieB]

Re: 50hp 3 cyl running fine until electrical check

Depending on which wires he selected, If he happened to choose the black w/yellow, thinking it was ground, and any other voltage source, he would have toasted the switchbox.

A spark test will confirm.

As for installing a tach, he needs to be sure of his wire selections, solid colors only and no wires with trace lines.

 

[Texasmark]

Re: 50hp 3 cyl running fine until electrical check

My serv manual for the 90 hp shows Grey for the sender (trigger pulses from the switchbox/rectifier or where ever on the engine), purple for switched 12v from the ignition switch, and black for return (ground). Would assume tachs are universal so if my 90 needed a tach and your 50 needed one, the same one would fit both hence the wiring would be the same.

Mark

 

[ronsealdeath]

Re: 50hp 3 cyl running fine until electrical check

Depending on which wires he selected, If he happened to choose the black w/yellow, thinking it was ground, and any other voltage source, he would have toasted the switchbox.

A spark test will confirm.

As for installing a tach, he needs to be sure of his wire selections, solid colors only and no wires with trace lines.

next
Hi thanks for the replies, when you say switchbox do you mean the powerpack? I'll check what wires were in the harness next week. on the note of popping the rectifier i assume this wouldnt affect ignition? It would just wreck the charging circuit?
Assuming i didn't hit said blk yel wire maybe the fuel is stale combined with bad plugs and oiling of the plugs?
I forgot to say the harness I was fiddling with was a Quicksilver 4 pin one. I have had a look and there appears to be no black/yellow wire in there so maybe I didn't fry the Powerpack/switchbox. Having said that it just seems weird that as I hooked these wires, the engine blipped then died. What could have done this in a 4 pin Quicksilver tacho harness??

Update - sorry keep editing this post! I have been looking at the wiring diagram and on my engine there appears to be a grey wire in the tach harness which would be the tach pulse. I can't see any yellow and black wires on the diagram? So what colour wire am I looking for on the switch box that would have fried it? Sorry, I'm making a mess of this post!
cheers
Al

 

[Texasmark]

Re: 50hp 3 cyl running fine until electrical check

next
Hi thanks for the replies, when you say switchbox do you mean the powerpack? I'll check what wires were in the harness next week. on the note of popping the rectifier i assume this wouldnt affect ignition? It would just wreck the charging circuit?
Assuming i didn't hit said blk yel wire maybe the fuel is stale combined with bad plugs and oiling of the plugs?
I forgot to say the harness I was fiddling with was a Quicksilver 4 pin one. I have had a look and there appears to be no black/yellow wire in there so maybe I didn't fry the Powerpack/switchbox. Having said that it just seems weird that as I hooked these wires, the engine blipped then died. What could have done this in a 4 pin Quicksilver tacho harness??

Update - sorry keep editing this post! I have been looking at the wiring diagram and on my engine there appears to be a grey wire in the tach harness which would be the tach pulse. I can't see any yellow and black wires on the diagram? So what colour wire am I looking for on the switch box that would have fried it? Sorry, I'm making a mess of this post!
cheers
Al

Are you paying attention or just an air head???????

 

[ronsealdeath]

Re: 50hp 3 cyl running fine until electrical check

Are you paying attention or just an air head???????

Excuse me? There is no need to be insulting. I am struggling trying to do all this from a mobile telephone so i apologise if i have missed something, the screen isnt ideal.
what i was inferring was that a grey tacho wire may connect to the powerpack/switchbox and would that react to 12v similarly to the blk yel wire referred to? I'm an amateur, a novice etc.... do be patient pplease we aren't all as clued up as each other
thanks
Al

 

[phebus1]

Re: 50hp 3 cyl running fine until electrical check

We're you testing in the main harness from motor to controls, or in the harness that comes out of the control box to dash?

 

[jbjennings]

Re: 50hp 3 cyl running fine until electrical check

If it were me, I'd start with an actual spark test with an air gap spark tester set to 1/4". If you 've got spark, you probably just flooded it and only need to probably dry out the spark plugs. If no spark, you've got a lot of stuff that needs checking before you go spending lots of money on a powerpack/switchbox. A burnt rectifier should only affect the charging circuit as you suggested, not ignition.
jBJ

 

[Texasmark]

Re: 50hp 3 cyl running fine until electrical check

Excuse me? There is no need to be insulting. I am struggling trying to do all this from a mobile telephone so i apologise if i have missed something, the screen isnt ideal.
what i was inferring was that a grey tacho wire may connect to the powerpack/switchbox and would that react to 12v similarly to the blk yel wire referred to? I'm an amateur, a novice etc.... do be patient pplease we aren't all as clued up as each other
thanks
Al

Sorry. Was having a senior moment.

 

[ronsealdeath]

Re: 50hp 3 cyl running fine until electrical check

Hello Phebus, it was what I assume is the tacho harness. Its a Quicksilver remote and has 4 pins on the end of the plug. I'll get a spark test going and see whats going on there.
One question I have on a spark test; As I will be on my own doing this, can I jump the starter solenoid by connecting the two large terminals with a screwdriver or similar? I take it the ignition key will have to be turned to first click? I don't think I could see the spark tester from the other end of the boat!
Thanks for the advice, hopefull at worst I just burned the rectifier.
Cheers
Al

 

[andrewddrennon]

Re: 50hp 3 cyl running fine until electrical check

A remote starter is than handiest, you buy them at oreilly`s for 20$ . But you could do the screwdriver jump.........Its just not terribly safe or effective...i prefer not to

If you get a remote starter put one alligator clip on the solenoid b plus terminal then the other to the small terminal with the yellow/red wire. Then just press the button to crank.


Or you could just have someone crank your motor over for you while you watch ........have the sparks plugs out if your using a single spark tester.

 

[phebus1]

Re: 50hp 3 cyl running fine until electrical check

I'm pretty sure that there are only four wires in that loom. Red-12+, Black-Ground, Purple- 12+ switched, and Gray- Tach. I would check the red wire coming off the solenoid on the motor and see if there is a fuse, and if so check it to see if it is good. If it is blown you would not get spark (not sure if engine would turn over though).

 

[ronsealdeath]

Re: 50hp 3 cyl running fine until electrical check

Thanks, I'll see if I can pick up a remote starter.

Interesting on the fuses as well. I searched and found one fuse which was fine and my manual didn't show where any others may be lurking. I'll have a good check over it next free weekend and see if there are any others.

Thanks again
Al

 

[ronsealdeath]

Re: 50hp 3 cyl running fine until electrical check

Hello there,

I got out of work early today so was able to do a spark test before dark. I hooked up my tester with a 7/16 (9mm) gap and had no spark on any cylinder. I reduced the gap down to a couple of mm so pretty much touching and got a spark on every cylinder. So I take it I haven't nuked my switch box. I cleaned the plugs and tried a start again, nothing. Tried with a load of EasyStart squirted in the carbs, nothing again.
My old Evinrude used to jump a 7/16 gap easy but this Merc won't do that. Also the spark only appears after say half a second or more of cranking. It just seems weak. Have I damaged the stator or something like that possibly?

 

[ronsealdeath]

Re: 50hp 3 cyl running fine until electrical check

Hi again, apologies for the double post. I consulted the manual today and went through checks on the stator that can be done with a multimeter. I also found a disc on the engine block which showed a number 9613246. Looking at some websites I think that makes this a 1990 3 cyl 50hp Merc with the Thunderbolt V ignition?
I used a mutlitmeter to check ohm readings between ground on the block to the blue stator wire and red stator wire (stator to switchbox). My manual said I wanted no cont. Red wire to ground gave 000 but blue wire to ground gave 900 on the Rx2000 scale. My manual says if any of these checks don't go as said in the manual then 'the stator assembly must be replaced'.
Is this absolutely the case? Would I be able to repair it? (low probability I know!).
Another book I have states
Any movement of the meter needle indicates a short to ground caused by frayed or melted insulation, or by a bad charge coil.
Is this just a case of buying a new stator or should I pull the flywheel and check for a melted wire or something? This appears to my limited knowledge to be in line with my problem of having a weak spark? Could I have melted a bit of the charge coil and thus grounded it out? In which case I could just free it up?
Sorry, another question, what part should I buy if I need to replace the stator?
Thanks
Al
Sorry for the million questions but I just wanted to be sure before buying expensive parts!

 

[ronsealdeath]

Re: 50hp 3 cyl running fine until electrical check

It was the kill switch grounding, black and yellow black and yellow as the song goes. Thank heavens its not a new stator!
Thanks for all your help guys, I'll open up the control box and sort. Maybe a new ignition module needed or something.
Cheers
Al