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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: EpsteintheSwami on March 22, 2015, 10:57:12 AM
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Hallo there,
Just bought myself a 1992 K75, and its seems to misfire a bit at low revs (between 1.5 and 2500 rpm), also can hear the occasional misfire when its idling. Apart from that it starts and runs fine, has bags of power and seems perfectly healthy, any idea what could be causing it?
Ive also noticed that it pops a bit on the overrun, only below 3000 revs or thereabouts
Any advice much appreciated!
Thanks
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greetings epsteintheswami...
welcome to motobrick.com...
whats the history of this moto... how abouts some photos...
j o
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Welcome to Motobrick.com.
Have a look around:
Search for "rough idle" (https://www.google.com/search?q=site%3Amotobrick.com+rough+idle&oq=site%3Amotobrick.com+rough+idle&aqs=chrome..69i57j69i58.11716j0j4&sourceid=chrome&es_sm=93&ie=UTF-8)
Search for "K75 misfire" (https://www.google.com/search?q=site%3Amotobrick.com+rough+idle&oq=site%3Amotobrick.com+rough+idle&aqs=chrome..69i57j69i58.11716j0j4&sourceid=chrome&es_sm=93&ie=UTF-8#safe=off&q=site:motobrick.com+misfire)
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as for the popping, they all do that.
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Popping could be a sign of air leakage somewhere in the exhaust. Maybe near the joint at the header or at the exhaust ports.
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Hi there,
Thanks for all your responses. Glad to hear the popping is normal for this bike, I'm new to fuel injected motorcycles and thought this might be a symptom of a lean mixture (or it might be as RBM says leakage in the exhaust, it does sound fairly loud although there are no apparent leaks)
Searched for K75 misfire and rough idling as suggested but haven't been able to find anyone with the same symptoms, all the related posts were detailing problems a lot worse than mine! As I said the bike is running brilliantly but it always hesitates and stumbles a little at low revs. The plugs look the right colour, nice pale brown in the centre, not sooty. I might change them just to be sure. From the little I know about fuel injected vehicles I think its possible the injectors might need a clean? If they're not atomising the fuel as well as they should then I suppose that would be most apparent at low revs. Anything else you think I should try before having them cleaned?
Don't know a great deal about the history of the bike except that its a 1992 with 57000 miles on the clock, completely original in good clean condition, clearly been looked after except for the fairing pockets being botched up and the side panels handpainted. Previous owner clearly didn't like cornering as the tires are worn a little flat in the centre, so until I get them changed I'm taking it easy. Still, had a good ride up the Hartside Pass yesterday, it was dry and sunny and I managed to scrape the pegs round a few of the corners. It surprised how wells these bricks can corner even with flat tires!!!
I'll get some pictures loaded up once I've found my battery charger.
Apologies for the lengthy reply!
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How is the idle balance on the throttle bodies? There are some threads about doing it on the forum.
No promises, but it might help the hesitation and the popping.
Chevron Techron in the tank will help with any crap in the fuel injectors.
Is there a seal where the headers enter the muffler? My bike backfired a lot more when that seal wasn't there.
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Problem solved!!!
Turned out to be a loose plug cap. Noticed it was loose when I had the plugs out, after putting them back in I noticed the misfire was gone, then a few miles down the road the bike lost all power and started running like crap. So took the plate off again to find it had came off completely this time. Got a new one ordered, in the meantime I've got a sock in there wedged between the plate and plug cap to hold it on, seems to be doing the job for now!
Just goes to show you should always check out the obvious stuff first before you start worrying about injectors and throttle body synchronisation and whatnot.
Hurrah!
Thanks for all your advice, next time it'll be a real problem I promise!
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A related question. Just bought my first street bike, made it a 1992 k75. Love at first site. Noticed some popping as mentioned as normal for all,that is good to hear for sure. I have noticed something a bit different with the idle and that is a semi-regular hiccup that has a mechanical/metallic sound to it. Occurs when at stop but not noticed at any other time. The bike runs great with only 21,000mi on it. Any ideas on this? Thanks.
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Problem solved!!!
Turned out to be a loose plug cap. Noticed it was loose when I had the plugs out, after putting them back in I noticed the misfire was gone, then a few miles down the road the bike lost all power and started running like crap. So took the plate off again to find it had came off completely this time. Got a new one ordered, in the meantime I've got a sock in there wedged between the plate and plug cap to hold it on, seems to be doing the job for now!
Just goes to show you should always check out the obvious stuff first before you start worrying about injectors and throttle body synchronisation and whatnot.
Hurrah!
Thanks for all your advice, next time it'll be a real problem I promise!
Just out of curiosity, did the plug have the threaded cap on the top of it? Some brands of plugs only come with the threaded stud and not the "cap" that the spark plug wire snaps onto.......
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Exactly. NGK specifies a D7EA plug for the brick engines. These plugs do not come with the nut that goes on the threaded terminal. You have to reuse the old nut or contact NGK support to get some sent to you. I got a dozen over the winter from NGK North America in Michigan.