Author Topic: Primary circuit resistance --- Fini!  (Read 2298 times)

Offline 1Sourdough

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Primary circuit resistance --- Fini!
« on: May 12, 2015, 09:10:07 PM »
I have been working around Strada #16 lately, and have a serious question about the values I read in different WG threads about the Digiplex ignition coil resistance.  One thread, dated three or four years ago gave the resistance as "Less than 1 Ohm, should be about 0.7 Ohms and both coils the same.  In more recent threads I am reading 5 to 8 Ohms.  

It appears the same coils are used all the way up to at least the year 2000, same appearance and same part number stamped on the steel frame of the coils.  How can the resistance be so different?  One poster even said he has coils which measure 3.5 Ohms so he installs a 1 Ohm resistor in series with the primary circuit so the coils won't overheat.  

Well, the coils on #16 are 0.7, and it's a little bit of a concern...  What is the skinny on this?

« Last Edit: May 19, 2015, 09:42:44 PM by 1Sourdough »
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Offline Kiwi_Roy

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Re: Primary circuit resistance
« Reply #1 on: May 12, 2015, 09:16:43 PM »
If they are both the same I wouldn't worry,
The secondaries should be the same also, they will be several thousand Ohms, measure them from the cap to chassis that way you will be measuring the leads also then measure the coil by itself, the difference is the cap and lead, should be ~ 5 kOhms
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Offline Wayne Orwig

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Re:
« Reply #2 on: May 14, 2015, 12:32:58 PM »
Very few people have good enough equipment to accurately measure anything near or below 1 ohm.

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Online Chuck in Indiana

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Re: Primary circuit resistance
« Reply #3 on: May 14, 2015, 02:10:10 PM »
Not to worry, Fred..there's a world of difference between coils used on points and computer ignition. The Aero engine uses the same coils as yours, they are new, and read .7 ohms on my Fluke. The 3-5 ohms you've been reading about is for points systems.
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Offline 1Sourdough

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Re: Primary circuit resistance
« Reply #4 on: May 14, 2015, 10:01:03 PM »
OK, thanks guys.  I'm using a pretty skookum Fluke meter, and since the readings came out solid, not wavering up & down, I figured they were what the coils thought they should be but...
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Offline 1Sourdough

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Re: Primary circuit resistance
« Reply #5 on: May 16, 2015, 10:57:38 PM »
Well, I went through the carbs, pulled all the plugs & hit the contacts with cleaner. Now it starts great and goes like stink up to about 4,000 RPM.  Within a couple hundred turns one way or the other it hits the governor like a brick wall.  Any gear, it just cuts out and falls off a few hundred turns before coming back to life, sometimes with backfiring.

After filling the tank with fresh gas I took it on I-35 and opened the throttle wide in fourth gear.  That sucker shut down right at 4,000 RPM and didn't come back.  With the clutch pulled the engine went to about Idle.  I coasted to nearly full stop before it showed a leg again.  Then it came back to life like nothing had happened, as long as it was treated kindly.  Took it home and parked it.
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Offline 1Sourdough

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Re: Primary circuit resistance --- Fini!
« Reply #6 on: May 19, 2015, 10:08:14 PM »
Well, now;

After thinking about it for a couple of days I finished the job.  Remembering another poster, (RK or Vasco DG perhaps?), writing that '90% of carb problems are ignition problems', I untangled the Digiplex module from the cables behind the fuse board, disconnected its cable, and along with applying copious contact cleaner, exercised the contacts for five minutes or so.  Then everything back together and let it sit for an hour to be really sure the liquid had all evaporated.

When I hit the starter it started right away, so off for a test ride.  Out on the highway it went through 4G RPM, (that's American for 4K, y'know), like it was never a stumbling point, and kept on going.  After several repeats to be sure there was no hang-up, we went to 5,000 & 5,500 several times.  #16 seems to have no memory of the bad times at all.  I even rolled up through 7,000 a few times, smooth as a baby's whatcha-may-call-it!

The only question I have at this point is something one of you who know about Digiplex circuitry may be able to answer:  Before unplugging the Digiplex cable I disconnected the battery, and as the cable slipped free I wondered whether some term may have set an incorrect flag in the ignition mapping - it does have some sort of map, doesn't it? - and perhaps removing battery power as my first step could have resolved the problem right away?

So what had been as solid a condition as someone flipping a switch has gone away, and I sure enjoyed that "test" ride!  Many thanks for the suggestions and encouragement on this and another thread I had opened about the situation.  I think the other thread related to hard starting, and it was there that most of the discussion occurred.

« Last Edit: May 19, 2015, 10:43:25 PM by 1Sourdough »
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Offline Wayne Orwig

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Re: Primary circuit resistance --- Fini!
« Reply #7 on: May 20, 2015, 08:20:55 AM »
 Before unplugging the Digiplex cable I disconnected the battery, and as the cable slipped free I wondered whether some term may have set an incorrect flag in the ignition mapping - it does have some sort of map, doesn't it? - and perhaps removing battery power as my first step could have resolved the problem right away?

I don't think the Digiplex has much in the way of smarts. It has some form of built in advance curve, and that is about it.
My 1994 had a problem, when new, with backfiring and popping. At the shop the mechanic burned up the starter when it backfired against the starter. It turned out to be the relay that feeds the Digiplex was bad, and the scrambled the Digiplex. So it needs a clean power connection for sure.
Scientist have discovered that people will believe anything, if you first say "Scientist have discovered...."

Online Chuck in Indiana

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Re: Primary circuit resistance --- Fini!
« Reply #8 on: May 20, 2015, 09:11:22 AM »
I don't think the Digiplex has much in the way of smarts. It has some form of built in advance curve, and that is about it.
My 1994 had a problem, when new, with backfiring and popping. At the shop the mechanic burned up the starter when it backfired against the starter. It turned out to be the relay that feeds the Digiplex was bad, and the scrambled the Digiplex. So it needs a clean power connection for sure.

Advance curve is it.  Digiplex is nothing more than an expensive switch.  ;D There's a wire that can be connected (or not) to change the advance somewhat. I forget what the difference is. If the bike doesn't immediately start, the trick is to cycle the kill switch, and it goes back to the starting advance curve. And.. yes. It needs clean power. DeOxit is your friend..
Chuck in (Elwood) Indiana/sometimes SoCal

02 Scura RC
87 AeroLario
79 G5
95 Skorpion tour
 
Sometimes it's easier to remember when you worked on something than where it is..

 

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