This started last fall.  It just falters sporadically for a portion of a second and then comes back so I THINK it's an electrical issue. Due to this issue I've been riding other bikes but now that summer is here I need to fix it.

My first thought was that it might be the fuel tank connector but I jumped that last fall and the problem persisted.  Also jiggled and remounted, the Motoronic connector, coil leads and a bunch of other stuff.  Still no joy.

It might be the ignition switch but when I took it out today neither of the needles blipped and the gauges and cluster backlighting didn't flicker so it doesn't seem to be a main power problem so I'm thinking it might not be the ignition switch.

I've got lots of parts around to swap with the exception of the Motronic.

Sometime in the next couple of days I'll pull the tank to inspect/wiggle all of that wiring.

Any suggestions?

It does sound electrical and the wriggle method will hopefully find it. I had a loose earth lead that caused the same problem. When it dies do you loose instrument lights, clock or any other electrical functions?
Regards Martin.

It doesn't die, just stumbles for less than a second.  Sometimes a few times in a row.

Neither the cluster backlights nor the speedo/tach glitch at all so it doesn't seem like a bikewide power issue. The RPMs obviously drop momentarily but the tach needle doesn't glitch but I suppose that's because the tach circuitry is damped some and the cutout is so short that it doesn't register on the tach.

It doesn't seem to happen under load as I did a few 85 MPH passes today and the bike ran solidly when accelerating hard.

It might be a loose spark plug lead.  I'm using some afttermarket Magencor plug leads so I'll try swapping in some OEM leads to see if that's the issue.

I have the same problem with my K75 (the one my wife was riding) been doing it for years and I still have no real idea what is going on. The only thing I can say for sure that it's electrical and probably causing fuel cut off.

I had a similar issue with a k100 I had in New Zealand.  Would usually cut out when I'd pull out to over take, which was both scary and bloody embarrassing!

To find the issue I inserted LEDs into the wiring wherever I could get one into and when it cut out I could see what LEDs were lit and what weren't.  It ended up being the fuel injection relay.  Replaced the relay and the issue was solved.

Because it was intermittent the LEDs being inserted was the only way I could determine it because it wouldn't fail with the bike running but standing still.

It could be the fuel level sender. I've corresponded with a couple guys who have experienced intermittent issues with that part, particularly with the wiring between the gas tight passthrough and the fuel pump wiring.  It is the last leg in the connection between the harness wiring and the fuel pump.  I would suggest swapping the fuel sender if you haven't already done so.

robmack wrote:It could be the fuel level sender. I've corresponded with a couple guys who have experienced intermittent issues with that part, particularly with the wiring between the gas tight passthrough and the fuel pump wiring.  It is the last leg in the connection between the harness wiring and the fuel pump.  I would suggest swapping the fuel sender if you haven't already done so.

Thanks. Yes, that had occurred to me as a potential culprit.  But I have half a tank of gas in the bike that I'll need to siphon out. I do have a spare FLS on hand and if swapping plugs/coils doesn't fix it then I'll try that next and also throw in a new fuel filter because it's only a $5 part.

But honestly the cutouts are so brief in duration that it doesn't SEEM to be a fuel delivery issue and seems more electrical in nature.

I really hate troubleshooting non-obvious intermittent issues but at least I have lots of swappable parts on hand.

Tesla13BMW wrote:I had a similar issue with a k100 I had in New Zealand.  Would usually cut out when I'd pull out to over take, which was both scary and bloody embarrassing!

To find the issue I inserted LEDs into the wiring wherever I could get one into and when it cut out I could see what LEDs were lit and what weren't.  It ended up being the fuel injection relay.  Replaced the relay and the issue was solved.

Because it was intermittent the LEDs being inserted was the only way I could determine it because it wouldn't fail with the bike running but standing still.

Interesting approach. Since you brought it up I'll try swapping in another fuel system relay and if that doesn't help then I can try your LED approach.

Had the same with a dizzy in a car .. used to be going fine and would stumble at 70 mph for about 1/2 second  (and was unable to replicate it at will) ...had a mind of it's own...took ages to track it down..turned out to be the coil wire to dizzy cap lead had some water get in and react with the copper centre plug and wire going to the dizzy cap (nice green colour which also went back up inside the wire)... resulting in high resistance at the cap end until it built up voltage and found a new track to earth to supply spark to the dizzy rotor and leads at the dizzy and run again. Cleaned up the green gunk in dizzy cap and fitted new wires and was end of problem.

When I first started using NGK Iridium plugs on this bike (about 16K miles) ago I read all sorts of awesome reviews (mostly on car forums) claiming they'd last for tens of thousands of miles.

While I was playing with the coils and plug leads today I figured I should take a peek at the plugs since the bike's also been a bit sluggish to get started lately.  Much to much surprise the NGK Iridiums look pretty darn worn after 16K.  When they went in they were all gapped at 0.024.  When I pulled them today they all measured in the 0.034-0.036 range.

Will be checking them a bit more often from now on.




Picked up and gapped some new DR7EAs tonight.  I'm guessing it will run a bit better tomorrow morning.

Never, ever assume that a new pack of spark plugs will all be good. I don't know what today's figures are but fifteen years ago the failure rate of new plugs was an average of 10%. I've has my fair share of duff ones straight off the shelf.

My 2C on iridium plugs in bikes? Crap. I've had nothing but trouble whenever I've tried them and always gone back to the 'bog-standard' type.

I've been running the NGK Iridiums in all of my bikes for several years now and haven't had problems.  I guess my expectations of oodles and oodles of miles from them was unrealistic.

I've seen riders claim more HP on the butt dyno and better mileage using iridium plugs but I haven't experienced that and I think that in the end with any decent spark plug in good condition that a spark is just a spark and an iridium-induced spark will not make your gas burn with any better compression or more efficiently.

I put a pair of Denso iridiums in my long-suffering CB250 and they were mega for the first 80 miles or so, great pick up and better midrange as if I'd added some ignition advance. Then they felt exactly the same as normal copper plugs. Then after 7K miles they were done for, one cylinder refusing to run in the wet and big scorch marks down the sides. It was quite pathetic when the standard NGKs that were in there before had done 25K.