Logo
FULL SITE MENU

Mercury 39 3.9 no spark

X

Xfakturx

New member
I recently picked up an old merc 39 that is not getting spark. I am not familiar with these old systems but it seems there is only a coil, condenser and point, I found a new condenser and replaced it but still no spark, I plan on replacing the point this week but if that doesn't work is there anything I can check before trying to order a new coil? Can I test the current coil?
 
Probably points, but follow Jeff's advice as well. Be sure to replace the water pump impeller too. These are good little motors but often get water in the lower unit as the shaft will rust (not stainless steel or plated) and damage the seal under the water pump. Be sure to check that out and replace before the lower unit gets damaged.
 
Appreciate the advice guys, as for wires to ground the motor only has 3 wires from what I see, positive and negative from the coil and a single wire to the condenser. I pulled the coil and had a maintenance tech at work check it with his fluke, its showing .6 ohm between +/- and 5780 on both readings between +/- and the spark plug output. Not sure what those readings mean.
 
That seems okay to me. How do the points look? Check for any resistance when closed. Has to be perfect continuity. Coils are really pretty reliable on these, not like Johnson/Evinrude, which tend to crack and arc to ground, or arc internally.
 
Got the motor running today, new points and plug wire did the trick, idles smooth and revs up clean. I did notice a small amount of yellowing froth in the water tub after letting it idle, is this the leak you were talking about? Also i didnt notice any water comiing out of a pee hole but I pulled the cowling and dont see where one even is?
 
Could be from old oil in exhaust chamber or leaking lower unit shaft seal as can be common. Water indicator is in lower housing on these 39's.....I think.
 
How can I determine it is getting flow and not overheating? And now that I have drained the gear oil how much do i need to put back in? Do i fill to the vent screw?
 
Take the hood off and run it,if you can hold your hand on the block for a minute without it burning the blazes out of you,you're good to go.Find the pee hole and poke it with a bit of fine wire or blow some air through it,it could just be a bit of dirt plugging it.
Fill from the drain plug,and when the oil appears at the vent,there's enough in.
 
The Tell Tale on those tends to plug with crud. Look for an opening at the right lower rear of the cowling and poke it out with a wire.

Suggest you check the LU oil to see if it's okay.

Jeff
 
Back
Top