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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: Kevin1100 on June 08, 2026, 04:37:29 AM
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This has already turned into more of a blog than just a forum post but oh well. To whom it may concern I guess, maybe someone else has the same issues or someone can point me in the right direction. Enjoy the read :laughing1:
I have now ridden my 1999 K1100LT for 1500 kms since buying it with 146k km on the odo. It was a non runner, the fuel pump and level sender had completely disintegrated. So I have no idea how it ran before and not sure how long it had stood before I bought it. Possibly years (indoors). I have done a lot of work on it but it is still running VERY rich. I always knew it was running pretty rich since my friends told me I would occasionally puff black smoke on acceleration and they would smell fuel/carbon, but after letting my friend ride in front of me on my bike yesterday, it's worse than I thought. I told him to ride it like he would on the track for a bit and a literal cloud of black smoke came out, for the whole duration of the acceleration. He said it pulled like a truck but it also looked like one of them old turbo diesel trucks!
Another problem is that every now and then, on HARD acceleration (3/4ths throttle to WOT), it will sometimes start hesitating for a bit halfway. It will start pulling hard, then completely stop pulling for about half a sec, and then continue pulling like normal. It feels like it's too long for a misfire and it's on all cylinders. Right now I'm theorizing that the engine gets too much fuel it can't burn off for a bit but I'm not sure. It's not backfiring.
What I did recently:
Synced the throttle bodies. It now idles much "calmer", less vibration and noise. I hardly even hear the engine running on idle with ear plugs in. It idles at around 800 rpm. Bit too low for my liking but it works for now. I'll try to tinker with the idle speed a bit more in the future.
Leaned the CO screw on the front of the CO mixture valve thing a bit. I turned it in until it started to run worse, then back out about half a turn.
I have fitted air pod filters on the throttle bodies, ditching the air box. It runs the same as before. The crankcase breather has a filter on it and the inlet above the timing chain cover is plugged.
What I did after I bought it, before riding it:
New spark plugs.
New fuel pump, filter and hoses.
Checked HT leads and coils resistance, all perfectly within spec.
Checked coolant sensors and air temperature sensor resistance at different temperatures, all within spec.
What I'm thinking now:
Pulling out the injectors to see spray pattern/leakage.
Checking fuel pressure. I've read that the vacuum regulated FPR goes bad on older bikes, but my later model doesn't have the vacuum line to the FPR anymore. Just the inlet and return. Both hoses are new so I can't imagine the return being blocked, although the return port in the FPR itself of course could be blocked.
Maybe checking timing? Not sure how to do that on this bike yet and by the way it runs it seems like the timing should be fine. I also don't think the hall effect sensors are going bad because temperature doesn't matter and there are no major running problems.
Replace the rubber boots from the cylinder heads to the throttle bodies. I can see them starting to crack. The cracks are very small and seem superficial so I don't think they're completely through, but it can't hurt to change them. I don't think an air leak would cause my rich running though.
Extra notes: I'm not burning any coolant. I am burning about 1 liter of oil every 1500 km so far but that seems to be within factory spec... I run between 13-15 km per liter of fuel, translating to 30-35 US MPG. I ride only backroads, mostly 80 km/h with lots of turns and bends so not the most economic. My bike doesn't have a catalytic converter or O2 sensor.
I would be very grateful for any insights on this by people with more experience with these bikes. I only have carburetted cars so the whole injection thing is new to me. Funny that I now have more trouble setting up an injected bike than a carburettor!
Little update: I took the injector rail off but couldn't do a spray test because the fuel lines are too short. I did however check resistances and injectors 1, 2 and 4 show between 22 and 28 ohms. Bit on the high side but maybe not too problematic. Injector 3 however shows very erratic resistances. It always settles around 25 but with the slightest movement of my multimeter it jumps to all kinds of numbers, sometimes showing an open circuit and eventually it settles back around 25. At first I pinned this down to my multimeter being a cheap POS but on the other injectors, as soon as my probes touched the posts the right resistance would show up and stay consistent even after moving the probes around. Measured them all about 5 times in total, each time #3 showed weird erratic movement. Might be time for an injector upgrade.
I also checked my spark plugs and all of them are quite black with soot and have a bit of oil on the threads. Not major oil deposits on the terminals so I'm not too worried yet, but I am seeing a few repairs in my magic orb. HT lead #2 was quite loose, I could pull it off with my fingers so that might have been the cause for the misfires on high load. I also checked my hall sensor plate and it seemed to be rotated a millimeter or 2 too far clockwise, past the notch. No idea if that would make a big difference but since the plate can't be rotated that much, I have rotated it back to match up to the notch exactly just to be sure. Sadly the weather is horrible so can't take it for a test ride now but hopefully this weekend.
Update #2: I pulled the fuel return line from the left side of the injector rail, inserted my manual bike tire pump with pressure gauge, opened the fuel cap and started pumping. Every time at exactly 2.5 bar I would hear air going through the return system into the tank. So I think my FPR is fine.
I also checked my TPS. I had to adjust it a tiny amount.
After doing all this I started the bike and it ran like it did before, didn't really notice a change but I'll admit I didn't have it running for long and it didn't get up to operating temperature. While cold though I could see black puffs coming from the exhaust even with just revving to about 2500 rpm. My hopes of it being fixed are low but we'll see in the weekend.