Intermittent running rough
Hi guys. I hoping someone can point me in the right direction. In the last couple of days, my K9 650 has developed an irritating fault. It runs fine on the highway, but stop/go in suburban streets is a bit hairy.
Intermittently, it decides to not idle when I cruise to a stop at a set of lights. The engine will die. I can twist the throttle a bit to control this, but when I go to take off, the engine bogs down. When I try to increase the revs to get more power, it stuggles up to about 3000 rpm, running quite roughly, but still bogs down when I start releasing the clutch. Generally, this clears after about 2 to 5 seconds, and the engine suddenly roars back to normal life. I then continue to ride normally until the next time it happens. That might be the next set of lights, or it might not happen for 5 minutes.
I also notice it sometimes on a steady or trailing throttle around 3-4000rpm, and it will stumble when I try to accelerate. It's only a quick stumble, maybe about a second, then the power is back on. So far, anything over 4000rpm is completely normal - no loss of power, excess vibration, or anything else I can notice.
My first inkling was last week when I went to start it at 0300 on a cold morning (5 degrees C / 40 F ). It didn't immediatly start like it usually does. After a couple of quick jabs on the starter with no luck, I held the starter button down for maybe 5 or 6 seconds, and it fired up. I've never had that happen before. It was probably the coldest its (ever?) been when I've started the bike, but it's still not that cold, and shouldn't cause any issues. But maybe cold enough to show up any underlying dodgy electrical connections? Anyway, after it eventually started, it ran fine, and I rode it for an hour to the airport. When I got back to the bike a couple of days ago, I was a bit dubious about how it would start, but it started fine. About 5 minutes in to the ride home, as I slowed for a set of lights that turned green as I approached them, the engine seemed to lose power. No warning lights, just felt like it had no power, and ran real rough as I tried to accelerate. I was just heading to the side of the road to pull over, and it came to life. I continued on to the motorway for an hour, then when I pulled in to my local streets, it did it once more. I rode it again yesterday, and it is getting worse.
Battery is a couple of years old, and reads 13.8v with anything above 1500rpm. Spark plugs are NGK Iridiums, about 40,000km old. Bike has done 80,000km. I pulled the plugs out, and they all look pretty normal - no black deposits or white burning. I'm wondering if a corroded connection might be affecting the FI? Why does it only happen at low revs? Fuel should be ok. I had 98 RON in it at the airport, and I filled it up on the way home with more 98 RON - no difference in performance. Annoyingly, it runs fine in the driveway at home - idling sweetly, and reving smoothly.
Can anyone offer some suggestions on where I should be looking?
SL125, XL250 (x2), GSX400/4, GSXR750, XT600 Tenere, VF1000FIIF (x2), Wee-Strom 09 abs