Ignition coils effed?

[birdy]

Howdy, I've been trying to diagnose my very stumbly idle and think I narrowed it down to the coils. It runs great above 2k rpm, but tends to stumble and sometimes die below that. No amount of carb tinkering has fixed the issue.

Here are the readings I got with my multimeter, which seem to be way out of spec:

2/3 coil: Primary 2.2ohms - Secondary: 22.5k ohms
1/4 coil: Primary 2.1ohms - Secondary: 28.15k ohms

Would coils with these readings cause a crappy idle?

Also: Mikes XS Green Coils seem to be the way to go. Worth the price?

Thanks Much,
Ryan
1979 Standard - "The Green Dragon"

[tinman905]

The green coils are my next improvement to my 80SG . From what I have read and what others have to say about them they are the way to go . For the benefits the price is well worth it. I'm sure someone else will chime in and give his 2cents worth

[Larrym]

Spare the Rod..Spoil the Pup.

Before you roll up a newspaper and hit the coils like you would a misbehaving puppy, "Bad coils....Bad! BAD Coils."

Twist off the end caps to the high tension wires and check each one visually and with a meter. Look for the notorious green corrosion lurking in our area and clean it off. Test each cap with a meter and look for readings out of the ordinary. It's a common practice to trim 1/4 inch off the end of the high tension leads and then reinstall the caps.

If just one of the caps are wonky then the cylinder won't fire. When the engine picks up RPMs the battery voltage increases and so does the amount of spark discharged. Enough to overcome the bad connection/wonky cap? Sometimes...

Spray/mist water on your exhaust pipes for a heads-up on whether or not one or more cylinders are misbehaving at idle.....

[skids]

Also, the plug caps can be rated different Kohms from one mnfr to another. To really test the coils, you should remove them and test wire-to-wire (if ya haven't done so already).

[birdy]

cool, thanks guys, I'll pull 'em off and test without the plug cables. See what I get.
___________
Ryan

[dbeardslee]

I had a similar problem with a set of mikes black coils. Ran better cold, but when it reached full operating temp it was a PITA under 2.5K - BAD stumble and no power. After going into the carbs at least 15 times, replacing carb boots, and a host of other stuff I finally replaced the coils. They were about all that was left to monkey with, and I hesitated to change them as they only had 7k miles on them. Replaced them with green mikes coils and the problem was solved. I would have preferred to try another set to confirm that they were bad before spending the bucks, but alas, I didn't have a spare set. Your problem sounds oddly familiar.

[b.walker5]

A cheaper alternative than MikesXS... maybe...

I recently looked at E with a veiw to buying it. I didn't, but... the owner had replaced his coils with second hand ones of an XJ650 and they worked great. They're 12volt so he didnt need the ballast resistor and he said they have a hotter output than stock XS11 coils. I havent seen figures to support that but the specs shouldnt be hard to find.

[dbeardslee]

They're 12volt so he didnt need the ballast resistor

Even the early model coils (78-80) are 12V - it's the primary resistance of the coils you have to watch. IIRC the 78-80's are 1.5 ohms, and the 81's and later are 3 ohms. 1.5 ohms need the ballast resistor, 3 ohms don't.

[bikerphil]

Yes, low RPM stumble can be caused by a bad coil even though it checks out OK with an ohm meter. Been thru that before. It's a problem that's hard to pinpoint.

[melbxs]

I have been ripped up on here before for saying this, but if a friend came to me with his newly acquired XS and asked for help to get it running A1, I would be inclined to say to him that he should come back when he has a new set of coils and HT leads in his hands.

Sure there are guys who run on old coils and leads OK, but the difference in terms of reliability and performance between old and new can be night and day.

I am positive that dozens of guys on here have stripped their carbs and triple cleaned them half a dozen times when the coils/leads were the problem. If you put in new coils and leads you can move ahead to working on the carbs in the knowledge that you are most probably in the right ballpark.

New coils and leads are a small investment for the benefits they bring.

[dbeardslee]

9 times out of 10 the problem with the stock coils is the 'permanently attached' high tension wires. When I originally installed hotter coils I thought I would hang onto to the stock coils as a spare. I had a 3 pound coffee can I was going to store them in, but when I put the coils w/wires in the can the high tension wires snapped in two. thirty year old high tension wires are just not a good idea. You can graft new wires into the old coils, and in most cases it will return them to factory spec. Unfortunately the old coils only put out about 16k volts, compared to dynas or black mikes coils (which I would not recommend) that put out 30k volts, or even better the green mikes coils that put out 75k volts. The hotter spark is immediately apparent at start up and improves overall throttle response. As far as tuning the carbs goes, you can usually get rid of the coil gremlin by just grafting the wires into the old coils.