Vintage K bike sudden death syndrome

[Beemer01]

Those of us who keep riding these older model seem to have experienced a rash of cases where the bike dies when hitting a bump, and sometime doesn't start. At this point, the fuel pump is inoperative, but everything else seems to work.

The culprit -in a number of these cases - is the connector to the onboard computer. All it takes is the slightest misconnection and bike dies. In my case I repainted the frame and failed to zip tie the connector bundle tightly and the dynamic movement of these wires was just enough to cause this problem. I subsequently have corrected this, but experienced a no start again yesterday - tapping the connector was enough to reseat the connector and she started up.

I have run a couple of connected black zip ties around the plastic housing and the metal ECM and cinched it tightly thus pressing the connector into the computer.

Others experiencing this might want to try this $.02 solution.

[hhshort]

I have 2 85 k100's and a 90 k75. The rational being that if at least one of them is running I have known good parts. At this point I'm not sure which components came with which bike.

My sudden death, with a bump, have been: 1. the fuel pump plug fell out of the gas tank and 2. the ignition switch needed cleaning.

My latest has been a "no start when hot". It would sputter and fuss like a flood but ususally would start. The fuel pump did run. The last time it did it with the whole rally watching and never did start. Of course everyone had opionions till I said I quite and hauled it home. I tested for spark Yes I tested for fuel pressure yes The plugs were wet so new dry plugs were tried,still no start. I could neither hear or feel the injectors and I don,t have a noid light. So what the hey! let's switch the computer from a bike that runs. Zip It Started with no fuss. I even put the old plugs back in and it started with no fuss.

Now since then I have ridden both bikes with the computers swapped, a couple hours and neither has given a fuss. It is one thing to fix a known defect it is another to wonder what you did to make it run.

OKAY!!!! Are there others that suspect that the computer connecter has gone intermittent on them?????? Harold

PS. I cannot think of the first K bike as being vintage when I remember seeing a new R69S in the show room. It was Dover white.

[cayuse60]

A coating of dielectric grease across the connector's contact area seems to be working for me so far...the rough roads in Maine keep me on the pegs, but all electrically controlled systems seem to be maintaining on my K75.:thumb ...so far.

[KCKBMOA]

I admit I didn't read all the previous, but here's a thought. I had a similar problem awhile back, freeway speed, shut down, not fun. I finally found the problem to be the wires at the ignition switch were broken from the steering flex. A new switch body fixed it, and some better routing may keep it at bay, I hope. BTW, if you do go there, the electrical part of the switch and lock assy CAN be replaced without major component disassembly.... I found out after :banghead Find a small red dot on the switch housing right side, looking through all the mess with a flash light. It's a bit of red laquer that covers the set screw holding the switch up into the housing. Once the screw is loosened, the switch can be dropped clear and pulled out to the left side. After removing it for the wire issue, I dissected it just for spite, and the contacts were so bad I'm sure they were on the way out anyway. KC

[motoedde]

Those of us who keep riding these older model seem to have experienced a rash of cases where the bike dies when hitting a bump, and sometime doesn't start. At this point, the fuel pump is inoperative, but everything else seems to work.

The culprit -in a number of these cases - is the connector to the onboard computer. All it takes is the slightest misconnection and bike dies. In my case I repainted the frame and failed to zip tie the connector bundle tightly and the dynamic movement of these wires was just enough to cause this problem. I subsequently have corrected this, but experienced a no start again yesterday - tapping the connector was enough to reseat the connector and she started up.

I have run a couple of connected black zip ties around the plastic housing and the metal ECM and cinched it tightly thus pressing the connector into the computer.

Others experiencing this might want to try this $.02 solution.

Another culprit is the fuel pump wire harness that runs along under the right side of the tank...that's a weak connector and can cause many a frustrating diagnosis.

[jdiaz]

I just replaced the fuel sending unit today on my bike, chasing down a thing from this summer when the bike would die at speed, but could be restarted before even coasting to a stop.

Look at the old and new designs.....there is a definite attempt at trying to reduce the stress on the wiring here:

http://jon.diaz.home.mchsi.com/temp/overmold.jpg

[GregFeeler]

Jon,
I got a smokin' deal on my very first K-bike - a K100RT - because the PO couldn't find out why it would die when hot and then start and run fine after 15~20 minutes. Turned out the spot welding of the ground tab on the underside (outside) of the fuel sender was coming loose and had corroded. With heat it would open up, then make contact again when cool.

[jdiaz]

Jon,
I got a smokin' deal on my very first K-bike - a K100RT - because the PO couldn't find out why it would die when hot and then start and run fine after 15~20 minutes. Turned out the spot welding of the ground tab on the underside (outside) of the fuel sender was coming loose and had corroded. With heat it would open up, then make contact again when cool.

I'm running out to the garage to check the old one. The failure mode on my bike is even more momentary than that.....the thing will start up 15 seconds after dying at 75mph. Its sorta like running onto reserve with an Airhead. :D

[GregFeeler]

I'm running out to the garage to check the old one. The failure mode on my bike is even more momentary than that.....the thing will start up 15 seconds after dying at 75mph. Its sorta like running onto reserve with an Airhead. :D

I was lucky in that this bike would be in failure mode for 10 to 20 minutes. I tested power on both sides of the plug to the tank, and then to the posts on the fuel pump and determined the ground was bad. THEN I pulled the tank and found the problem. You could see the corrosion on the ground tab. Big AH HA! moment.

[rinty]

I've never had a K, but the exotic problem I've been told about by a K owner is an undersize battery ground wire. The fix is to replace it with one of a one guage lower number (the wires get thicker as the guage numbers, go down, right?).

The symptom was that the bike would be running at normal highway speed and then suddenly shut down. A number of techs attempted, unsuccessfully, to diagnose the problem, until the owner took it to a dealer in Arizona, who immediately knew what it was.

Rinty

[jdiaz]

I've never had a K, but the exotic problem I've been told about by a K owner is an undersize battery ground wire. The fix is to replace it with one of a one guage lower number (the wires get thicker as the guage numbers, go down, right?).

The symptom was that the bike would be running at normal highway speed and then suddenly shut down. A number of techs attempted, unsuccessfully, to diagnose the problem, until the owner took it to a dealer in Arizona, and who knew immediately what it was.


I've changed a few of our K bikes to the new-style ground wire, although it isn't just one size larger. It looks like double-ought welding cable compared to the original piece of twine. :laugh

[breyfogle]

... an undersize battery ground wire. The fix is to replace it with one of a one guage lower number (the wires get thicker as the guage numbers, go down, right?).

A heavier ground cable might possibly improve starting with a marginal battery by allowing a bit more current flow but I do not see how it could have any effect on an intermittent running problem. I suppose the original cable could have an internal break , but then replacing it with any cable (thick or thin) would fix the problem.

[cayuse60]

A heavier ground cable might possibly improve starting with a marginal battery by allowing a bit more current flow but I do not see how it could have any effect on an intermittent running problem. I suppose the original cable could have an internal break , but then replacing it with any cable (thick or thin) would fix the problem.

Agree...most electrical problems are connections and clean grounds. A little maintenance on both each year keeps my K75 trouble free....except my horn is intermittent:gerg ...does that come with age?

[jdiaz]

A heavier ground cable might possibly improve starting with a marginal battery by allowing a bit more current flow but I do not see how it could have any effect on an intermittent running problem. I suppose the original cable could have an internal break , but then replacing it with any cable (thick or thin) would fix the problem.

I think it is a leftover theory from the '85 K100 models, which had such poor grounding that the electrical system would sometimes try to use the throttle cable as a grounded return for the brake light switch or heated grips......and melt the sheath around the cable.

That's why the heated grip kit has that extra ground wire to pass from the right-hand assembly to the ground point under the gas tank . :D