MMI coil question

[ndutton]

Does anybody know the secondary (output) voltage of a Moyer coil?

[Dave Neptune]

Neil, you will get a big variance on output voltage from the coil due the varying voltages supplied. Kind like using the "R" termin l to start then switching to the resistor.

I'd like to know the voltage at 11v supplied like in starting with older batteries and also at 14v.

I'd be curious as the wattage of the volts. I worked with some really really hot CDI's on some radical 2 strokes and one of the guys in the shop literally burnt a tiny hole through his "misplaced and poorly timed" thumb placement. The burns on each side of the thumb were tiny and the guy was in agony for a while.

Dave Neptune

[ndutton]

The reason I asked was I heard a local Sunday morning radio talk show host (Leon Kaplan on KABC, the Motorman) mention plug gaps are typically different on points vs. electronic ignitions. A little more research suggested it wasn't so much the triggering mechanism as it was output voltage, 25~30KV vs. 40KV and higher, 0.035" for the lower output, 0.045" for the higher. Coil saturation due to greater dwell of EI was a factor too but not the driving force. I checked my MMI coil on the spare engine and there was no labeling so I thought I'd pursue it on the forum.

I considered trying different plug gaps when we were digging through the EI/coil failure issue. Once we grabbed hold of increased dwell, coil saturation and ignition system current regarding EI, somehow the plug gap idea didn't seem that important anymore.

[Dave Neptune]

Neil, plug gaps on point type ign were always set tight due to the points and signal breaking down as things wore out. It was also common to close the gaps down for Hi performance applications to get a good spark at higher RPM's due to this break down. With the EI and the fact that it does not break down allows for larger gaps all the way up to higher RPM's without having to reduce the gap.

I have used in the past now for over 30 years an EI on the A-4. The first set up I adapted and made my own "shutter" for the photo optic trigger. I always used the Champion RJ12-C (marine) plugs and set them at ".042 LOOSE" slip in the gap. The wider gap has two distinct advantages first it provides a "broader" spark for idle and the wider gap also warms the plug a bit at idle for better idle quality and far less fouling if oil burning is a problem, this gap will not change the heat range of the plug for operational power when needed. And the wider gap at higher RPM's just gets the fire started far better for overall performance that does not break down for a really long time. I used my plug for 3~4 years and never noticed any difference when replacing them. I also used my cap & rotor for at least 5~6 years and the wires were my third set in 34 years of never failed me A-4 operation.

Dave Neptune

[ndutton]

Thanks Dave. It pretty much confirms - or encourages - me to give the wider gap a try.

[Vermonstah]

Neil, plug gaps on point type ign were always set tight due to the points and signal breaking down as things wore out. It was also common to close the gaps down for Hi performance applications to get a good spark at higher RPM's due to this break down. With the EI and the fact that it does not break down allows for larger gaps all the way up to higher RPM's without having to reduce the gap....

Dave - your detailed explanation here is very helpful. I have an EI from MMI sitting in the box, awaiting install. Provided that my boat and engine emerge from this winter without any surprises in store for me [a big IF], then I plan to undertake the conversion from points to EI.

[sastanley]

I have installed new plugs this spring gapped at a loose .040" (J8C)..the engine is still winterized and I have a few parts missing from the motor that are essential, like the dizzy and a half rebuilt accessory drive, so I haven't test run it yet.

Vermonstah...the switch over is easy provided you've heeded all the various precautions related to coils with EI that we've discussed over the years. If you have everything in your boat relatively normal, Neil's calculator should help determine the sizing of the resistor. If you have a newer Moyer coil, it probably has sufficient internal resistance to handle the different dwell characteristics of running EI.

Knowing your input and output voltages (and coil resistance) will be helpful in determining coil life, as the purpose of putting a resistor in line is to reduce input voltage to the coil.

One last tip...While replacing the points plate with the EI plate, make sure you clean out the distributor and clean/lube the advance weights. If you hold the distributor gear still and try to rotate the top of the dizzy shaft, you should see it force the weights in and out if they are operating freely. It does not take much crud/rust/dirt to make these malfunction and get stuck.

I hope everyone gets the quarterly (??) Moyer newsletter via e-mail...Don wrote about primary and secondary ignition circuits in the newsletter I just received.

Here is a link provided my our Admin in another post - http://www.moyermarine.com/newsletters/2-1-17.html

[Vermonstah]

... Vermonstah...the switch over is easy provided you've heeded all the various precautions related to coils with EI that we've discussed over the years. If you have everything in your boat relatively normal, Neil's calculator should help determine the sizing of the resistor. If you have a newer Moyer coil, it probably has sufficient internal resistance to handle the different dwell characteristics of running EI. ...

.

Shawn - thanks for the words of encouragement and the reminders of previous insights. I have been hesitant to undertake the EI conversion - I finally got things dialed in with the points but I am willing to attempt it.

I have a MMI coil, two years old with approximately 200 hours. I would be willing to invest in a new MMI coil and move the current one to my spares inventory if it makes sense to instantiate EI with a fresh coil.

Thoughts and opinions on whether to obtain a fresh coil before converting to EI welcomed and appreciated.

[sastanley]

There should be no reason to replace your coil..However(!!!) a call to Ken or Don to confirm that the coils they were carrying when yours was purchased is of sufficient resistance may be prudent. That is where a resistor may come into play if you need more resistance.

The first thing to do is to remove all wires and measure the static resistance of the coil with an Ohm meter.

[BunnyPlanet169]

(Shawn beat me to it)

Vermonstah - MMI has only had one coil on their website for a couple years now - so if it's MMI, and 2 years old, you're probably fine.

Measure its resistance with everything disconnected - as long as it's at least 4 ohms or up you should be all set. I remember the MMI is about 4.2 ohms. Without going back in the threads - and oh there are threads - the design goal of EI is current safely less than 4A.

[JOHN COOKSON]

If you know the coil's history from the time it was first installed to present you should be good with the present coil if:
The internal resistance is correct, it has never over heated, and you have not had any coil related shut downs.
You might take a voltage reading at coil + when the engine is running to be certain you will not be pumping to many amps through it.

TRUE GRIT

[Vermonstah]

Thanks to all for their responses.

Apologies to Neil if I have hijacked his thread.

It will be some time yet before I can get to the boat and take some readings on the internal resistance. Boat is still covered in ice and snow and lake temps at 33 degrees and holding steady

I can attest to no overheating of this coil, nor coil related shutdowns. Which also makes it a good candidate for my spares box. But I will run the resistance tests and confirm with Ken the specific vintage of this coil.

I will report back on my attempts to convert to EI.

Thanks again.

[ndutton]

Apologies to Neil if I have hijacked his thread.

No apology necessary. I'm thoroughly enjoying the thread and the quality of responses.