1985 Mercruiser 3.0L 140 ignition

[Krectedwerds]

Hi everyone, first post.
I scanned through a few dozen threads in search of an answer for my problem but couldn't find anything.
The problem: Bought the boat as a project, didn't run and had been sitting a few years. I cleaned out the fuel lines, new filter, new plugs and wires and it started. Ran like **** so I killed it. Now I have no spark. Was the coils last stamd I suppose. I just got the new coil and it's totally different from the one that was in it. I believe the one that was in it was an automotive style, had a two wire plug (further investigation it was spliced into harness). The new coil looks like the proper one, but says "use with external resistor". I have no clue how to go about that. Does anyone have any idea how that works? Or is the boat already set up for it and I just install it and go? Any help is appreciated!
Side note: It is still setup with points in distributor, single black wire from there to I'm assuming the ground for the coil.

 

[stonyloam]

You are already set up for it. The "external resistor" is the purple wire going to the coil +. The problem is far more likely to be the points than the coil. If you do not get a spark with the new coil, change the points. I take that back, you SHOULD be set up for it. You should have a purple wire running from the electric choke to the coil. If that has been replaced, there is no telling what you have. Was the old coil plug spliced into a purple wire?

 

[Scott Danforth]

the coil usually NEVER is the issue. about 2 our of 10,000 changed are ever bad

did you file the points?
did you set the points? if so, what was the gap?
what was the dwell that you were reading on the dwell meter?
what did you set the timing to?

if you did not file the points (even new points), set the gap, adjust the dwell, then adjust the timing, you simply threw away money on a coil.

 

[Krectedwerds]

The coil was in fact bad, tested open on ohm meter. I will have to go check when I get home about the purple wire, I believe it is there but I am not sure. Will update later on. As far as points, I did file and set gap, got spark then the old coil quit. I am hoping all it is is the coil.

 

[Krectedwerds]

I am new at this so it will be a learning curve. I do not know what the "dwell" is or how to check it?

 

[stonyloam]

Dwell angle is the length of time that the points are closed expressed in degrees of rotation of the distributor cam. A dwell of 30 means that the points are closed for 30 degrees of rotation (out of 360). That allows current to flow through the coil to " charge" it. If too short, the coil will not developed full voltage, if too long the coil could overheat. It is set by changing the points gap. You use a dwell meter to set it, like this: https://www.amazon.com/Sinometer-Au...744436&sr=1-1&keywords=dwell+meter+tachometer . You will also need a timing light to set the timing after you get the dwell set.

 

[Scott Danforth]

I am new at this so it will be a learning curve. I do not know what the "dwell" is or how to check it?

I would start by googling points ignition 101. Plenty of videos, how-toos, and the whole theory behind points

 

[Krectedwerds]

I would start by googling points ignition 101. Plenty of videos, how-toos, and the whole theory behind points

I will definitely look into that. Learning process over here lol

 

[Krectedwerds]

Thank you stonyloam, I appreciate the response and the link. I will be getting back to the boat this weekend hopefully. I did some pictures of the wiring, and found the purple wire no longer goes to the coil, yes still mounted on carb. Guess someone hacked this thing back together. Great. I do have the manual for this engine so hopefully I can find a wiring diagram for the ignition circuit, fingers crossed!

 

[stonyloam]

Well there are 2 purple wires, one coming from the ignition that operates the electric choke, the other is the resistance wire that is supposed to go to the coil +. Where does the coil + wire come from now?

 

[Krectedwerds]

Ok,
Purple with yellow stripe is + from starter to coil +.
Found purple from carb, it goes all the way past coil in harness, wire that was tied to + was white (factory loop) still strapped in paper tape.
Single gray from harness and black from distributor to -
I believe that's how it's supposed to be, as long as the white wire is in fact my resistance wire.

 

[Krectedwerds]

I did manage to find the diagram in the manual for this engine. Everything is right, except the purple wire from choke to coil +. I'm digging through harness now to see if white wire is spliced to purple at the harness connector by the circuit breaker

 

[Krectedwerds]

Both purple and that white wire are spliced together at the harness plug, so that white wire should work for my resistance, correct?

 

[stonyloam]

Well no not necessarily. Purple wires are related to the ignition. There is a purple wire that goes from the ignition switch to the electric choke. That wire is just regular stranded copper wire. There should be a second purple wire running from the choke to the coil +. That is a purple wire that has a resistance of about 1.5-1.8 ohms. That provides reduced voltage to the coil when it is running. The purple/yellow wire from the starter bypasses the resistance wire when the starter is turning. So anyway that purple resistance wire needs to be in the circuit going to the coil +, if you have a coil that needs an internal resistor.

 

[Krectedwerds]

The purple wire is in the circuit to the coil +.
After hours of digging and figuring out what wire does what, she now has spark! Still a no start though, but one step at a time I guess haha.

 

[Silvertip]

Did you get the dwell (point gap) set properly. Engine doesn't need to run to do this. Timing at least needs to be in the ball park for the engine to run. So far you have one out of three things needed (spark). The engine also needs fuel and spark needs to happen at the right time.

 

[stonyloam]

Yeah, grab a timing light and check the timing. When you get that right the next thing is fuel.