Coil? Never had a coil go bad.

[Tycer]

Mercruiser 140. Recurring issue. Dwell and timing set. Run a couple of hours and it dies. Below 3200 rpm seems ok. Above and she dies. Fuel ok. Vent ok. Filters ok. Jets squirt fine.
Hook up the meter. No spark. No dwell. Pull cap, put cap HV lead from coil to a decent gap from ground. Operate points manually. Weak, thin orange spark. Put it all back together. Have a snack. Five minutes later she starts and runs at 3k a couple more hours.
Coil?

 

[alldodge]

Does the coil have an external ballast resistor or wire?
What is the value?

 

[Tycer]

Does the coil have an external ballast resistor or wire?
What is the value?

The coil does not need a ballast resistor and is being fed 12 V

 

[Tycer]

Does the coil have an external ballast resistor or wire?
What is the value?

Do I have to test resistor wire while the engine is running?

 

[alldodge]

The motor has points so there will be 2 feeds to the coil.

One without any resistance feeding the coil full 12V for starting (purple/yellow wire)
One "with" resistance feeding the coil once it starts (purple "see dotted wire)

Resistance is measured with ignition OFF and using an ohm meter

 

[Tycer]

The motor has points so there will be 2 feeds to the coil.

One without any resistance feeding the coil full 12V for starting (purple/yellow wire)
One "with" resistance feeding the coil once it starts (purple "see dotted wire)

Resistance is measured with ignition OFF and using an ohm meter

Right. So no resistor wire. Probed next to the boot on the purple wire and the ring end. Infinity ohms. Only about 20” of wire.
Checked resistance on coil. 3.4 ohms on primary, 8,070 ohms on secondary.
Checked condenser by charging with ohms setting on multimeter and then switching to dcv and observing voltage that slowly dissipated.
Shows spark through my cheap spark tester. Gapping the coil HT wire out to 1/8” still gives spark snap but it’s certainly not bright.
Shouldn’t it be a thick bright blue spark?
spark plug wires and coil HT all have resistance in spec.

 

[alldodge]

So no resistor wire. Probed next to the boot on the purple wire and the ring end. Infinity ohms.

Without a resistance wire the coil will overheat. When it overheats, sparks going to stop

I'm seeing you need 3.0 ohms resistance or ballast

The spark should be white or blue spark

 

[Tycer]

Without a resistance wire the coil will overheat. When it overheats, sparks going to stop

I'm seeing you need 3.0 ohms resistance or ballast

The spark should be white or blue spark

The coil states no external resistance is needed. It is an internal resistance coil. If what I’ve scoured on these forums is correct, external resistance coils have about 1.5 ohms and the external resistance is an additional 1.5 equaling 3.0 ohms resistance and this coil at 3.4 internally is already greater than the 3.0. If I add resistance I’ll go even higher.
I did find the connection on the (-)side of the coil was not real tight. It is now.
I have disconnected the tach to see if that has any bearing. I’ll take the boat out again Wednesday and see what happens.

 

[Scott Danforth]

The coil states no external resistance is needed. It is an internal resistance coil. If what I’ve scoured on these forums is correct, external resistance coils have about 1.5 ohms and the external resistance is an additional 1.5 equaling 3.0 ohms resistance and this coil at 3.4 internally is already greater than the 3.0. If I add resistance I’ll go even higher.
I did find the connection on the (-)side of the coil was not real tight. It is now.
I have disconnected the tach to see if that has any bearing. I’ll take the boat out again Wednesday and see what happens.

you have the wrong coil then. the ballast is needed for the points (points die quickly at 12 volts, however live for a long time at the 9 volts after the ballast.)

here is something from the stickies

https://forums.iboats.com/forum/eng...-up-your-engine-with-points-ignition?t=335302

 

[Tycer]

Without a resistance wire the coil will overheat. When it overheats, sparks going to stop

I'm seeing you need 3.0 ohms resistance or ballast

The spark should be white or blue spark

Ok got the correct coil. I do have a resistance wire. It’s too short. Only has 0.6 ohms resistance. That plus the new coil gives 2.1 ohms. Sigh. I’ll order the proper wire and solder it in. In the meantime I have a 1.5 ohm ballast resistor wired in and I have 3.0 ohms combined and a nice blue spark. The other coil when combined with the short resistance wire was giving 4.0 ohms resistance and the electric choke was connected to the positive terminal of the coil.
I’ll take her out tomorrow afternoon. Wish me luck.

 

[alldodge]

Good luck, and you may be ok as is, measure the voltage at the + side with the motor running

 

[Tycer]

Good luck, and you may be ok as is, measure the voltage at the + side with the motor running

Ok. Now we’re talking. Picked the purple wire before the plug and put a 1.5 ohm ballast resistor to the 1.5 coil. NAPA ECH IC10 and ECH ICR11.
Ran her both with and without the tach hooked up. No difference. The new setup runs like it should. 1+ hours a WOT And both the coil and the resistor were relatively cool.
Got the boat Labor Day weekend and this is the first time out she’s not died.

Best of all I got a rare (really rare) high five from my wife!

 

[Tycer]

[No message]

 

[alldodge]

That's a classy looking old gril

 

[Howard Sterndrive]

you have the wrong coil then. the ballast is needed for the points (points die quickly at 12 volts, however live for a long time at the 9 volts after the ballast.)

points don't care if the resistance is in the wire before the coil or 3 inches further along, inside the coil. and even if one uses the wrong coil without resistance, the points won't be affected- too much coil voltage will burn out 100 wrong coils and the points will still be fine.

The only difference will be during cranking, the original wiring and coil would provide a hotter spark for starting when resistor bypassed, which can't occur when the resistance is in the coil, but unless someone is boating in the winter, a boat will start fine with an internal resistance coil.

Napa 1C14SB is the only quality internally resisted coil though. The one they sell at TSC etc is junk and only last a few hours when bracketed to the engine vibrating away...

 

[Tycer]

points don't care if the resistance is in the wire before the coil or 3 inches further along, inside the coil. and even if one uses the wrong coil without resistance, the points won't be affected- too much coil voltage will burn out 100 wrong coils and the points will still be fine.

The only difference will be during cranking, the original wiring and coil would provide a hotter spark for starting when resistor bypassed, which can't occur when the resistance is in the coil, but unless someone is boating in the winter, a boat will start fine with an internal resistance coil.

Napa 1C14SB is the only quality internally resisted coil though. The one they sell at TSC etc is junk and only last a few hours when bracketed to the engine vibrating away...

I wonder if my coil is getting too much voltage. 12.38 while running. 14.6 system voltage.

 

[Scott Danforth]

points don't care if the resistance is in the wire before the coil or 3 inches further along, inside the coil. and even if one uses the wrong coil without resistance, the points won't be affected- too much coil voltage will burn out 100 wrong coils and the points will still be fine.

The only difference will be during cranking, the original wiring and coil would provide a hotter spark for starting when resistor bypassed, which can't occur when the resistance is in the coil, but unless someone is boating in the winter, a boat will start fine with an internal resistance coil.

Napa 1C14SB is the only quality internally resisted coil though. The one they sell at TSC etc is junk and only last a few hours when bracketed to the engine vibrating away...

you are correct....the points dont care about resistance, only about voltage and current...... which leads back to resistance.