Merc 140 no spark...

[JoeD1988]

Re: Merc 140 no spark...

Check for spark with an alternate method. Put a piece of carton between the points and a jumper lead on the hot side and ground (so basically short the points). Then turn on power and hold center spark lead to a big bolt on the block (not touch but almost). Remove the jumper lead for a short period and a spark jumped from center lead to the block. That way you can test it without trying to start.

Tried that, I did not get a spark from the coil wire, just a big nasty spark from the neg. side of the coil.

 

[thumpar]

Re: Merc 140 no spark...

Do you have a tach hooked up? I have heard that can cause problems. Otherwise it kind of sounds like a bad coil.

 

[JoeD1988]

Re: Merc 140 no spark...

I've tried it with the tach unhooked and hooked up, no dice either way.

 

[Hoosmatroos]

Re: Merc 140 no spark...

Remove the wires from your coil and measure the resistance from the coil. From + to - should be very low (1-2 Ohms or so) and from + and - to the center should be around 10K. Please check that before going further.

 

[JoeD1988]

Re: Merc 140 no spark...

Remove the wires from your coil and measure the resistance from the coil. From + to - should be very low (1-2 Ohms or so) and from + and - to the center should be around 10K. Please check that before going further.

Disconnected all wires from coil, and checked for continuity/ohms between the tower of the coil and both terminals of the coil, nothing on either. Checked for continuity/ohms between the 2 small terminals on the coil and get 1.7 ohms.

Done.

 

[thumpar]

Re: Merc 140 no spark...

Done.

Not testing for lack of continuity you need to ohm it to the tower too.

 

[JoeD1988]

Re: Merc 140 no spark...

I did. That's what the post says. My meter checks continuity/ohms simultaneously, I get no ohms from the tower of the coil to either side. I get 1.7 between the positive and negative sides of the coil.

 

[Don S]

Re: Merc 140 no spark...

I did. That's what the post says. My meter checks continuity/ohms simultaneously, I get no ohms from the tower of the coil to either side. I get 1.7 between the positive and negative sides of the coil.

Replace the coil.

 

[Hoosmatroos]

Re: Merc 140 no spark...

Yup, coil is toast.

This is how it works:

+ side on the coil is the blue lead coming from the key. Blue windings are the primary side of the coil with a few windings to ground via the points. The red part of the coil is connected just after the primary coil ends. Red part of the coil have lots of windings and should be around 10K Ohms. Red part is called secondary. Normally when the points are closed (same with electronic ignition but without the points) the coil builds up a field and when the point open, the field collapses and a high voltage is generated within the secondary side (just the nature how coils work). The condenser is there to absorb the spark that otherwise burns the points.

 

[JoeD1988]

Re: Merc 140 no spark...

OK. That's what I was thinking the first time I checked resistance from the tower and didn't get anything. Bad coil. Awesome. Thanks guys.