Intermittent cut out

Hi people-
I'm a newbie here, though not to motorcycles, with 40 years in the saddle. I recently picked up an '82 KZ1100 bagger, and have a problem that has me stumped. It will start and run fine, then one cylinder will cut out, maybe two, then it will clear out and run on four again. Seems to be when I roll off the throttle and coast, then roll back on that the problem usually occurs, though sometimes at constant speed (low rpm and throttle opening.) Under acceleration, sooner or later the dead cylinders will kick back in.
Some background and diagnostic history: 17,000 miles on bike, K&N filter (from the looks of it) and aftermarket (H-D restrictive) mufflers. First time this problem occurred I pulled the plugs (shut down while it was running on two) and was surprised to see no fouling. Plugs show maybe a little lean, if anything. Replaced plug wires and coils with new/known good parts. WIth plugs out and grounded, cranking the starter showed weakish spark on 1&4, none on 2&3. Switch black/green primary leads, problem follows wiring, not coil. Did pickup coil resistance check and igniter test as per Clymers, within normal range.
Does this sound like a likely candidate for the coil relay mod? The rolloff/roll on business makes me suspect carbs, but as we know, if it sounds like carbs...
When it cuts back in, it's like flipping a switch, and when it's running on four, it makes good power. Whatever carb flukes it may have, I can't help thinking I need to chase down an electrical gremlin.
Thanks in advance for any help.
RoMoMoTo

To answer your question regarding the coil mod, I suggest you measure the voltage at the coils. Measure both. It could be the voltage going to your coils is intermittent. If the coils test good, the problem is either the voltage supplying the coils or you have a defective ignitor or pickup coils.

First check coil voltage on both sides. If it is less than 12VDC with the bike not running, you would benefit from the coil mod. Once installed, you may still have the same basic problem. Then, get a factory service manual and follow the troubleshooting steps for troubleshooting the ignitor and pickup coils. If you don't have this stuff, drop me a note and I will type out the steps. The checks are not difficult but there are quite a few and I don't remember how to do them off the top of my head and have to refer to the service manual.

If you find that either the ignitor or pickup coils are bad and one or the other most likely is, you might want to go with a Dyna S as NOS replacement parts are more expensive and used ignition parts are questionable, at best... I say this from personal experience. If you get back to me in this thread and I don't respond, and need quicker help, see my vintage carb forum on my web site. I look at that at least daily. Good luck.

PS: One last thing occurs to me... before doing anything else, trace the wires from the right hand pickup coil to where they go to the ignitor and make sure they are connected securely. Then trace the wires out of the ignitor; especially the green one and make sure it is secure as well. Clean any connector and grease the connections with dielectic grease. This could be the problem as well.

Post edited by: wiredgeorge, at: 2006/06/26 07:52

Thanks, Wiredgeorge. I'll check the items you mention and post results.
RoMoMoTo


Bikes? '82 KZ1100, 2004 DL650, 2002 DR650, a pair of Norton 850 Commandos

Wiredgeorge-
I ran a temporary jumper wire to the coils, as there was considerable voltage drop through the stock wiring. Fired right up, ran great, went a half mile down the road and stopped to shoot the breeze with a neighbor. Started the bike up again after 15 minutes - running on two.
Came home and checked resistance from the pickup coils and found the 1&4 coil good, the 2&3 coil resistance way off. Connections all seem good. Starting to look like a bum pickup coil, and time to go with a Dyno S, eh?
RoMoMoTo

You can get pickup coils off eBay pretty cheap BUT they are used ignition parts. I never have had much luck with used parts. A Dyna S would take care of the problem without the hassle of buying used parts. www.z1enterprises.com has very good prices on a Dyna S. Kind of up to you... if you can get a cheap used pickup coil and try it, it might work out for you but it is riding season for most folks (if it doesn't) hehe

I too doubt the wisdom of buying used electronic ignition parts. I have a Dyna S on order; expect to see it before the week's out.
YEP; it's riding season alright. That's why I try to always have 2 or 3 running motorcycles in the shed at any given time. Otherwise I'd go crazy every time I have a breakdown. Hey, I've been a Norton guy for 25 years. NO WAY am I going to be stuck with only one motorcycle...
RoMoMoTo