1999 K1100LT fuelling/ignition issue

[Dovafish]

Hello there, I am the (somewhat) proud new owner of a 1999 Ex police K1100LT here in the UK, with 39k miles on the clock. The fellow I bought it from had it sat idle for the past four years or so, however kept up with replacing filters and fluids yearly as he knows being sedentary is bad for a bike. About six months and 200 miles before I purchased it, it had new: Plugs, brake fluids, coolant, oil, oil filter, air filter, back tyre and battery. seeing the mileage, I asked if he had lubed the clutch splines, which he hadn't, but the previous owner had.

Reason for writing is that the first time I took the bike out for a proper run (two days after purchase), after about two hours on the road, it started cutting out under power at certain rpm ranges. I first noticed it when giving it the beans in second, when it hit 6k it kind of 'coughed' and removed all power for a second, then carried on, albeit with the brake light warning triangle illuminated. Ever since this, it has been spluttery between 3k and 4k revs, with the tach needle dipping whenever the engine has a momentary loss of power. Other than this, no other electrics seem to have been freaking out, other than the red warning triangle, which now won't go away when I touch both brakes, and will stay on until I bring the bike to a halt and power cycle it. In some hears (mainly third), it will lose power over 6k rpm, almost like it's hitting the limiter, but rougher. Whenever there are these dips in power, some mighty backfires will come from the exhaust... I've had a look at the fuel filter which is dated 2007, and ordered another out of principle - however unsure if it could be a fuelling issue over an ignition problem, the backfiring suggests an inconsistent spark to me.

Here are two videos of it happening, firstly of me in fifth gear maintaining between 3k and 4k, notice the needle dropping and the camera shaking as the bike lurches. I am under a constant cruising throttle here.


The second video is of me in third gear, then giving it wide open throttle, as if on a motorway slip road or overtake, before the engine tops out at 6.5k rpm, stops giving power and backfires loads.
https://youtube.com/shorts/50psWyUDWXo

It isn't in every gear that power delivery tops out at 6.5k, first and second hold on a bit higher before the issue comes into play. (didn't test how high fourth and fifth would go for obvious reasons)

I'm baffled as for the first two hours of this ride it was performing perfectly, it seems a rather large issue to just come on out of absolutely nowhere. I let the bike fully cool down in a Tesco car park before limping it home to test if it was an overheating hall effect sensor, which made no difference. As far as I can tell from the manual, the red warning triangle on the dash is solely for brake light or ABS failure, both of which I tested to be working fine while the lamp was illuminated.

The seller was a genuine bloke and had MOT evidence to show that the bike was suffering severe lack of use compared to his other bikes, and that it had been taken care of as much as was reasonable for a garaged bike.

There seems to be other people having similar issues, although none identical to mine, and they all seem to have vastly different solutions, even down to something as unrelated as the sidestand switch. This is my first bike with any kind of technology on it so I'm in pretty far over my head.

Any help welcome
Tom

[Scott_]

My 1st suggestion would be to get yourself some electrical contact cleaner(like DeOxit or similar) and clean every wire connection you can find.
All ground connections at the frame, transmission, Motronic plug(damhik), coil connectors, fuel tank connector, injectors, etc... you get the idea. 
Especially the side stand switch mounted down on the bottom of the bike, clean it out real good and make sure the tang has good contact with the mechanism so it's mechanically being operated properly. It's not uncommon for the tang to get deformed and cause electrical ignition issues.
While you are doing that, be sure to look for any bare wires(unintentional grounding), or any that may be pinched somewhere. Being a former LE unit, anything could be possible with their modifications for added on options.

Also get some Techron fuel system cleaner and run in the fuel for a couple of tanks to help clean out the injectors on the inside.

I'm at the beginning stages of resurrecting my '97LT and this is something I need to make sure I do as well(it's been sitting for 6yrs)

[Laitch]

In addition to Scott's observations, and while you're resting, the 19 year-old fuel filter is a prime suspect, especially in a neglected Brick with a fuel tank that may have contained aging fuel, or a dampened fuel filter that could have been a growing medium for fungus and bacteria eventually causing intermittent clogging of its filtration. Update us after you've installed the new filter. Did you get a Mann, a Mahle or some other type?

What is the resting voltage of your Brick's battery?

[Dovafish]

Not too knowledgable on forum etiquette so not sure how to reply to both messages to avoid filling the thread up.

Scott, I have a dwindling supply of deoxit hanging about that I gave a blast on all of the pins to the ECU brain - then plugged and unplugged it a few times to let it scrub itself clean some, thought it wouldn't do any harm. I'll order some more and then go about cleaning all the connections, I hear some of the sensors use microvoltages which don't play nicely with corrosion from Scottish winters. I've got some generic stuff (loads cheaper), however I find that deoxit keeps dust and crackling out of music gear for longer so it must be better, Which is a shame for the old wallet...
I plan to disconnect the sidestand switch entirely, I like parking a bike on the sidestand and subsequently warming it up on there before I got for a ride. I know its technically removing a safety feature but I always remember to flip it up before putting the bike in gear anyway. There's a bunch of baffling wiring on this bike that I'm going to have to trace or theorise purposes for, such as and older style windscreen three-position switch by the ignition, but also on the switchgear by the left thumb as I believe is common for an LT of this year. Another point is that the battery cradle is missing so the battery does wiggle around somewhat, however couldn't move in such a way to short itself on anything, although I've gone to the effort of ordering a new clamp and screw set for it.

Laitch, I got a Mahle filter as it's what came up on motorworks when I searched my model name. The tank had more crusty stuff and bits of that white flaky corrosion from the metal and rubbers on the filler cap than I would have liked, so I wiped up what I could and decided to buy two filters, to perhaps swap a second time in a couple weeks or so if the first replacement has sucked up the rest of those particles.
Battery is brand new and has only ben on the bike for two weeks tops so I don't think it would be a failure point but I will check tomorrow when I drown the bike in Deoxit.

Thanks for the tips! Fingers crossed it's this fuel filter, even if it's not then it definitely needed replacing anyway, so there's a silver lining.

[Edward]

Fuel pump. Replace it. They are cheap enough. Check your internal hoses are in good shape and connected.

[daveson]

Also, replace all the fuses, even if they seem good, they're deliberately the weakest link in the system, so deliberately easy to get to.

I had a similar issue with my K100 that sat for years before I got it. After a while the issue disappeared, I think I shook the cobwebs out of it.

Reason Other than this, no other electrics seem to have been freaking out, other than the red warning triangle, which now won't go away when I touch both brakes, and will stay on until I bring the bike to a halt and power cycle it.

Does the tail go out, or go dim when the bulb monitor light goes on?

The bulb monitor warns you if the brake circuit, or tail light circuit is faulty, the second that the problem starts. After your two hour ride, the two hours of good vibrations may have loosened the earth connection at the plug in the tail piece. This sometimes results in parallel circuits turning into series circuits, with the voltage not being good enough.

[Scott_]

Also, replace all the fuses, even if they seem good, they're deliberately the weakest link in the system, so deliberately easy to get to.

I had a similar issue with my K100 that sat for years before I got it. After a while the issue disappeared, I think I shook the cobwebs out of it.

Does the tail go out, or go dim when the bulb monitor light goes on?

The bulb monitor warns you if the brake circuit, or tail light circuit is faulty, the second that the problem starts. After your two hour ride, the two hours of good vibrations may have loosened the earth connection at the plug in the tail piece. This sometimes results in parallel circuits turning into series circuits, with the voltage not being good enough.

I dirty lamp socket connection can give the BMU issues.
Over the years I have read of others having issues with lamps that have a brass shell as opposed to the original nickel/polished lamp shell.
Also note that the BMU doesn't play nice with LED lamps without a load resistor(to fool the BMU).

[Dovafish]

Update after half a day's work:

I went through and blasted every electrical connection I could reasonably find with electrical contact cleaner, and in the process found out that the back brake pedal was only intermittently illuminating the brake light. I checked the function of the switch, which was fine (and blasted it with contact cleaner anyway) then took the tail light apart to clean that giant connector that serves all the lights back there. It was properly oxidised, with one of the female spades being slightly bent as well. After cleaning, fixing the bent spade and re-assembling, my indicators now flashed the brake light instead of the indicators. Huh... I took it apart, unplugged and replugged the big connector and all was fine again. I also cleaned all the HT leads, coils and fusebox, of which all fuses were happy. If the problem persists, I'll try replacing them all. I also bypassed the sidestand switch entirely, if you remove the bullet connectors from the plug they're in, you can push fit a blue double ended crimp onto them, then squeeze a little to make sure they don't vibrate loose, then crimp a bit of wire between them on the other end. Pretty pleased with myself as it's both elegant and non destructive to the bike's wiring.

Something that a friend of mine picked up was that the airbox snorkel had come loose, letting the airbox get the majority of its air directly into the side. This was due to a missing screw allowing the snorkel to pivot instead of be fixed. We found a spare screw for it, and duct taped the snorkel to the airbox where it enters for good measure. Not sure if this could have caused an issue or not, my previous carburetted Honda NTV ran happily however it was getting air, but my K11 Micra won't start if I remove its airbox snorkel, so I guess it could go either way.

I bought a new length of fuel line and will be attaching that to the new fuel filter when it arrives tomorrow, then testing things out! It seemed foolish to test it unfiltered or with the old one when I have a brand new one arriving tomorrow.

Will update everyone tomorrow evening with my findings!

[daveson]

After cleaning, fixing the bent spade and re-assembling, my indicators now flashed the brake light instead of the indicators. Huh... I took it apart, unplugged and replugged the big connector and all was fine again.

The indicators are wired in parallel, the brake circuit is a separate circuit. If we imagine that the earth contact at the plug in the tail is too week, earth will be lost at the rear, then the brown earth wires can become positive, these lights are now connected by a positive like wire. Now for example, if the indicators are used, there is now an earth from the indicator circuit, to complete the circuit, this intermittent circuit would cause the brake light to flash like indicators. Plugging it in again probably helped to clean the contacts or improve them. It could probably do with a closer look.