Dual station ignition problem, weak spark, not the coil.

Hey folks. I'm up against the limits of my understanding and need some guidance.

Twin crusader 327s circa 1965ish. Dual control stations. Mallory distributors with electronic ignition. Mechanical fuel pump and Rochester 4gc carb freshly rebuilt. I'm getting fuel and I have compression, but there is a spark issue I'm trying to track down.

Starboard engine is running great. Port engine was running fine but recently changed behavior. Would only start and run from the fly bridge switch, but the main helm switch also had to be in "run" position.

Replaced the helm switch with new. No change.

Tested both coils (port and stbd) and they read the same for primary and secondary windings. Swapped coils to confirm, starboard engine still runs great and no change to port engine. Rules out the coil.

Today, I discovered that the Ammeter light on the fly bridge instrument panel tested high for resistance. Replaced the light with new. While under the instrument panel, replaced several other loose terminal connections.

Turned the key at the main station and it started up when given enough throttle. Ran fine over 1500 rpm, but died below that.

With the key at the main helm in run position, started the engine from the fly bridge switch and it started much easier and ran fine above about 1000rpm, but then died when I pulled throttle below that. With both keys in run position, started the engine again, let it run at 1200rpm, then shut off the fly bridge key, engine died immediately. Tried the same thing again but switched stations (fly bridge key in run, then turned off the main helm switch) it ran for about 5 seconds then died.

I suspect a weak spark at low rpm, which is exacerbated when only one switch is in the run position. This makes me think it is a poor ground somewhere.

Am I on the right track? What should I do to further isolate the problem?

I'm really new to DC electrical and just feeling my way through, so any help is greatly appreciated.

It sounds like you are on the right path, Electrical is a pain and you just have to keep at it. On another note I was surprised when you said you were running the 4GC carbs. I thought I was the only person left running them. Have a great 4th of July

missnancy said:

On another note I was surprised when you said you were running the 4GC carbs. I thought I was the only person left running them. Have a great 4th of July

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Usually people are surprised that I'm running 327s. They always say, "you mean 350s, right?" But aside from measuring bore and stroke, everything about these engines indicates 327, including the notes in the original owners service manual from the original owner of the boat.

I'm not romantic about the 4GCs and they're a little fiddly to tune, but now that I've rebuilt them they should be good for another several seasons.

Thanks for the encouragement on the electrical. I'll keep at it, but man, what I would give to go back in time and take a few courses on how this stuff works. Happy Fourth!

replaced the ballast resistor?

I'd check the primary circuit, with a test light and a volt meter to ensure integrity in that circuit....

makomark said:

replaced the ballast resistor?

I'd check the primary circuit, with a test light and a volt meter to ensure integrity in that circuit....

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Can you walk me through a simple how to?

makomark said:

replaced the ballast resistor?

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Coil is part #27270 and marked with "Use without external resistor". When I tested the coil, it gave me 3.1 Ohms on the side terminals and 6,810 at the center terminal. The other coil gave identical readings. According to the testing procedures I found online, the side terminal resistance is higher than expected, and the center terminal resistance is on the low end. Again, I swapped the coils between Port and Starboard and the problem did not follow the coil. So I'm not sure what to think about this.

Wow!....seems like there have been several changes to your boat over the years....

First off, have two ignition switches controlling one engine is not a good way to get the intended control functions. its usually best to have a separate start stop panel at the 'secondary' location and have the ignition switch at the 'primary' location. so you need to understand how the ignition switches are interconnected. how did you start an engine up in the past before the issue occurred?

as far as testing the ignition, without a ballast resistor, you should have +12VDC at the + terminal of the coil with the ignition ON. the module (points replacement) will open and close the - terminal to cause the spark, based on engine rotation. I prefer a test light with a bulb that will draw at least one amp of current...using a voltmeter may show the volts but that may fall off with the current load increases (if there's bad connection in the circuit)..

Another item to note, a bad tachometer will inhibit the ignition system so a good first step is to disconnect the tach wire at the - terminal....it may be gray but hard to say...check the back of the tach and find the wire's color there...hopefully, it will be one piece.

makomark said:

Wow!....seems like there have been several changes to your boat over the years....

First off, have two ignition switches controlling one engine is not a good way to get the intended control functions. its usually best to have a separate start stop panel at the 'secondary' location and have the ignition switch at the 'primary' location. so you need to understand how the ignition switches are interconnected. how did you start an engine up in the past before the issue occurred?

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I agree that it isn't ideal and it's on The List of Projects. Prior to this issue, both engines would start and run from either station.

makomark said:

as far as testing the ignition, without a ballast resistor, you should have +12VDC at the + terminal of the coil with the ignition ON. the module (points replacement) will open and close the - terminal to cause the spark, based on engine rotation. I prefer a test light with a bulb that will draw at least one amp of current...using a voltmeter may show the volts but that may fall off with the current load increases (if there's bad connection in the circuit)..

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Thanks for this. I will test and see what I'm getting. FWIW, after a little searching on that particular coil, it seems that it's pretty outdated AND was spec'd for a 6 cylinder. If I were to replace the coil, what am I looking for, and will there be additional modifications necessary, such as adding a ballast resistor?

makomark said:

Another item to note, a bad tachometer will inhibit the ignition system so a good first step is to disconnect the tach wire at the - terminal....it may be gray but hard to say...check the back of the tach and find the wire's color there...hopefully, it will be one piece.

Click to expand...

THIS MIGHT BE KEY. I've noted for the last couple of years that the tachometers at the flybridge both read low, and I think the port reads lower than the stbd (although I cannot recall for certain). I'm inclined to delete the tach and try to run her, just to see what happens. The tachs are original Faria from 1968. They're cool, but they might be better as paperweights. We'll see.

jbh425 said:

THIS MIGHT BE KEY. I've noted for the last couple of years that the tachometers at the flybridge both read low, and I think the port reads lower than the stbd (although I cannot recall for certain). I'm inclined to delete the tach and try to run her, just to see what happens. The tachs are original Faria from 1968. They're cool, but they might be better as paperweights. We'll see.

Click to expand...

Well whaddya know... I discovered a loose terminal nut on the back of the port tach on the upper station. Tightened it down and she fired right up! Both tachs still read low, but that's a more tolerable situation.

Thanks makomark for your tips.

Getting back to the start\stop for the secondary station: can you describe or point me in the direction of a wiring diagram for how to do this? And any advice on choosing the switches for an exposed (fly bridge) location?

Sounds like you may have a bunch of potentially loose connections....may be worth the time to check everything you can...

On the start stop panel - you really want one in place of another ignition (key) switch. The issue with two keys is they both have to be off to stop the engine....you could wire them in series (for the ignition circuit) but then you have to access both to start or secure the engines....too complicated in an emergency....

the panel itself is two momentary switches, one for the ignition (STOP) and one for the starter (START) circuit...and these are paralleled to the master (KEY) ignition switch circuits (IGN & START). Once started at the master station, the panel can stop the engine or restart it if it fails. If you dont have a ballast resistor in the primary ignition circuit, you probably want one for the panel's STOP function. I will dig up a schematic and post it later...as far as the switches themselves, I prefer the MIL-SPEC water-tight type....they aren't cheap but they don't leak/corrode/rust either...

Here's one I copied from a merc manual.

the STOP button grounds out the ignition circuit = no spark....the START button supplies +12VDC to the slave solenoid via the YEL/RED wire....the engine is started from the <single> key switch at the master helm. Turning it OFF disables all functions at both stations.

If you have the original mid-60's harness, the colors may be different...