errantspark
New member
Hey all, proud new '87 K75 owner, reporting in!
Picked her up for a song ($500) a couple weeks ago. 46k on the clock, eng oil, filter, gearbox flush, final drive flush, brake fluid flush performed recently by BMW SF. I'm planning on diving deep and doing all future maintenance (within reason) myself. I'm real excited to build up my understanding of the whole bike top to bottom.
When I picked the bike up it felt anemic, had a lot of afterfire on decel and the fuel economy was quite poor (20mpg!! at one point). Turns out one of the spark plug cables had come loose, after re-attaching it the bike has been a lot more well behaved and I've averaged about 46mpg over the last 200 miles. I'd like to keep riding this bike for another 150k miles so I wanna take real good care of 'er.
Overall everything seems ok, there are a few things on my radar to check out:
First off the bike brubles and occasionally afterfires fairly noticably when decelerating with no throttle. I hear that some K bikes just do this? I'd like to resolve the issue though if possible. I've checked the TPS contacts and they're nice and clean. Not sure where to go next?
Second off, the idle seems... rough or maybe lumpy? It doesn't stutter so much as wander, spending 10 seconds at 1050 then 5 seconds at 900 then 7 seconds at 1k etc etc. The idle doesn't stay at the same RPM even when warm. Just now (warm engine, coming off 40 mile ride) I had the bike on the center stand upon starting idle climbed to 1200 then fell back down to 1050, in this state holding down the starter button would raise the RPM to about 1200. Blipping the throttle wide there'd be a half second or so of hesitation/chugging before the engine would revved up. Once I've taken it up past about 2k and the alternator kicks in the idle drops down to about 750, and starts sounding a bit worse. Maybe I just need to adjust the idle screw? Taking the bike off the center stand and leaning it LEFT seems to RAISE the idle RPM and leaning it RIGHT seems to LOWER it. When the bike is leaned left the throttle seems more responsive and holding the starter raises the RPM less, when leaned right the opposite is true.
This seems like some sort of fuel delivery issue to me. I can't imagine a vacuum leak that would be affected by the tilt of the bike right? However it's an old bike and the rising RPM when hitting the starter seems like there might be a vacuum leak AND some sort of fuel delivery problem. Really unsure though, the afterfire seems to indicate a rich mixture to me, yet vacuum leak would mean it's running lean?
I've dumped half a can of Seafoam in the tank, and I'll finish it off at next fillup to see if perhaps that helps the problem. Other than that I'm not sure where to start? Pull the gas cap and check the fuel filter and pump seems easiest. After that send the injectors to Mr. Injector? I've got a new set of spark plugs on the way, and maybe I'll grab a new air filter as well.
Overall though, I love this bike, such a blast to ride! Looking forward to many more miles.
Picked her up for a song ($500) a couple weeks ago. 46k on the clock, eng oil, filter, gearbox flush, final drive flush, brake fluid flush performed recently by BMW SF. I'm planning on diving deep and doing all future maintenance (within reason) myself. I'm real excited to build up my understanding of the whole bike top to bottom.
When I picked the bike up it felt anemic, had a lot of afterfire on decel and the fuel economy was quite poor (20mpg!! at one point). Turns out one of the spark plug cables had come loose, after re-attaching it the bike has been a lot more well behaved and I've averaged about 46mpg over the last 200 miles. I'd like to keep riding this bike for another 150k miles so I wanna take real good care of 'er.
Overall everything seems ok, there are a few things on my radar to check out:
First off the bike brubles and occasionally afterfires fairly noticably when decelerating with no throttle. I hear that some K bikes just do this? I'd like to resolve the issue though if possible. I've checked the TPS contacts and they're nice and clean. Not sure where to go next?
Second off, the idle seems... rough or maybe lumpy? It doesn't stutter so much as wander, spending 10 seconds at 1050 then 5 seconds at 900 then 7 seconds at 1k etc etc. The idle doesn't stay at the same RPM even when warm. Just now (warm engine, coming off 40 mile ride) I had the bike on the center stand upon starting idle climbed to 1200 then fell back down to 1050, in this state holding down the starter button would raise the RPM to about 1200. Blipping the throttle wide there'd be a half second or so of hesitation/chugging before the engine would revved up. Once I've taken it up past about 2k and the alternator kicks in the idle drops down to about 750, and starts sounding a bit worse. Maybe I just need to adjust the idle screw? Taking the bike off the center stand and leaning it LEFT seems to RAISE the idle RPM and leaning it RIGHT seems to LOWER it. When the bike is leaned left the throttle seems more responsive and holding the starter raises the RPM less, when leaned right the opposite is true.
This seems like some sort of fuel delivery issue to me. I can't imagine a vacuum leak that would be affected by the tilt of the bike right? However it's an old bike and the rising RPM when hitting the starter seems like there might be a vacuum leak AND some sort of fuel delivery problem. Really unsure though, the afterfire seems to indicate a rich mixture to me, yet vacuum leak would mean it's running lean?
I've dumped half a can of Seafoam in the tank, and I'll finish it off at next fillup to see if perhaps that helps the problem. Other than that I'm not sure where to start? Pull the gas cap and check the fuel filter and pump seems easiest. After that send the injectors to Mr. Injector? I've got a new set of spark plugs on the way, and maybe I'll grab a new air filter as well.
Overall though, I love this bike, such a blast to ride! Looking forward to many more miles.
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