Sure ccould use some expert help on this ignition issue

[flyingvranch]

Hi All. I am at my wits end trying to diagnose an ignition problem and any help or advice would be much appreciated!
I have a Johnson 35 HP 1978 motor. New rebuild. I have all new ignition components. Under the flywheel I have a new charge coil and a new sensor. I have two new ignition coils and a new power pack. I have carefully wired each component and have good grounds on everything. New plugs.

What is happening is that I have a hot spark on one coil only. The other coil has nothing. I have swapped out various plug wires and secondary wires and by process of elimination I can get the non working coil to spark just fine also if I plug it in to the working hot lead from the power pack. I cut out the plugs and soldered the wires directly to the power pack leads to eliminate a possible bad plug. It appears that I am getting voltage out of the orange wire only coming out of the power pack and not the orange/blue wire for the other cylinder. The spark is very hot and in fact jumps nearly 1.5 inches from the ignition coil.

Please tell me if I am correct in my understanding about the CDI ignition process. When the flywheel magnet passes the charge coil it sends voltage down to the power pack. When that SAME magnet rotates around and passes the sensor the power pack sends voltage to an ignition coil that fires the plug spark. Is that correct? The flywheel has two magnets and so when the next magnet rotates around the power pack sends the spark to the other coil. Is that correct also?

I have inspected the flywheel and the magnets look good and nothing is hitting anything. Would the timing have an effect on this or perhaps be causing this? I have installed an electric starter that is spinning the motor very fast (plugs are out). I did notice that the new starter bracket does not have a hole for the high speed timing screw. Is that a problem? Also I have no battery charging circuit as I plan on manually charging the starter battery anyway when it gets low.

Sorry about all of the questions and the long post, but this really has me stumped.

[frankr]

Your understanding is basically correct. A magnet passes the charge coil, generating a voltage that is stored in a capacitor in the power pack. The magnet then passes the sensor, which sends a small voltage to the power pack that signals a SCR (electronic switch) to send the voltage from the capacitor to a coil.

The second magnet with North and South poles reversed repeats the process, except the polarity of the voltages is reversed. The reversed polarity signals another SCR to send the voltage from the capacitor to the other coil.

So, common sense says that the difference between #1 and #2 is the two SCRs responding to different polarities. Since there is only one charge coil providing both polarities and one sensor doing likewise, the only thing that makes sense is you have bad SCR in the power pack.

I think I said that right

EDIT: To clarify, there are two SCRs in the power pack. First one responds to a negative voltage from the sensor and the second responds to a positive voltage from the sensor. One of yours is shot.

[frankr]

quote FrankR:

Your understanding is basically correct. A magnet passes the charge coil, generating a voltage that is stored in a capacitor in the power pack. The magnet then passes the sensor, which sends a small voltage to the power pack that signals a SCR (electronic switch) to send the voltage from the capacitor to a coil.

The second magnet with North and South poles reversed repeats the process, except the polarity of the voltages is reversed. The reversed polarity signals another SCR to send the voltage from the capacitor to the other coil.

So, common sense says that the difference between #1 and #2 is the two SCRs responding to different polarities. Since there is only one charge coil providing both polarities and one sensor doing likewise, the only thing that makes sense is you have bad SCR in the power pack.

I think I said that right

EDIT: To clarify, there are two SCRs in the power pack. First one responds to a negative voltage from the sensor and the second responds to a positive voltage from the sensor. One of yours is shot.

EDIT EDIT: Of course the problem could also be a bad coil, except you said you eliminated that by swapping coils. So it isn’t the coil.

[flyingvranch]

I sure hope that’s not the case. That’s a brand new Sierra power pack that I cannot return. I am going to do some more testing tomorrow and double check everything. Thanks for helping me also!

[billw]

It wouldn’t be the first time a new one of those packs were bad. You say all the stuff is new….Why? Power packs can last five minutes or five decades. You never know. Age doesn’t seem to be a factor. A pack is not something that I would be personally replacing as a service item, like points and condensers. Do you still have the old pack? Was it working? Can you at least use it as a test? Too bad you cut off the plugs but you could at least use test leads, to try it…..

By the way, be careful working with the coil primary and charge coil wires….there can be a couple of hundred volts lurking there.

And finally, letting the spark jump an inch and a half, while impressive, is not a good idea. At some point, the electricity is going to decide that it’s easier to go through the internal insulation of the coil, than it is to jump such a large gap. If that happens, you will also be needing a new, new coil.

Long live American manufacturing!

[jerry-ahrens]

: While I’m not a big Sierra fan, they do have a good warranty…. at least that’s what I’ve been told. Your retailer should be able to get the faulty part replaced. Sierra even pays shops warranty for labor. I would suggest checking each amphenol (rubber connector with pins) connector to make sure you don’t have a pin that was backed out when you plugged them together. The bad part about all of this , is we have two sources of parts for OMC ignition parts. Sierra is one, and CDI Electronics is the other. The latter makes BRPs ignition stuff, for the most part. I have had issues with both. Sometimes, I end up on Ebay, to buy new old stock OMC parts for some motors. Be sure to only deal with sellers who will back up the part in case it’s defective.

[fleetwin]

Like others have said, expecting the spark to jump 1.5" is unrealistic, and could damage ignition components. I am assuming you closed the gap down to a gap between 1/4-1/2" and restested.
I’m sorry that you cut off the rubber amphenol connectors and soldered the leads, but I guess that rules out bad connections. You swapped the coil primary leads which made the other coil fire, which more or less rules out a bad coil. I am assuming there is no stop lead in the circuit, and nothing is plugged into the other side of the black/yellow lead in the three pin connector.
I think I read that you have checked ground leads with an ohm meter and saw readings less than one ohm.
How did you set the charge coil/sensor coil air gap under the flywheel? I realize that an air gap that is too big would probably affect both cylinders, but you never know….
If all of the above is OK, sounds like you bought a defective pack, which happens. Why won’t Sierra honor the guarantee?

[flyingvranch]

This morning I swapped out power packs and the same exact problem is still going on. That tells me it’s not the power packs? I pulled the flywheel and looked at the magnets. They look OK but one side is noticeably stronger than the other side. I am going to try to adjust the charge coil out towards the magnets as far as it will go without hitting anything. Thanks all so far for the good advice. Sooner or later we will get to the bottom of this!

[flyingvranch]

Here is a photo of the mag plate with the coil and sensor. Do they look mounted OK? Can the coil possibly be mounted upside down with the wires on top and still work properly?

[mic-57]

I am not sure if this link will help or hurt http://www.cdielectronics.com/wp-conten … 202012.pdf.
At this point with all that you have tried I would suspect the flywheel. If one magnet is weak it will not trigger the corresponding SCR in the module.

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