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Author Topic: 85 K100RS - Won't start. Starter spins but that's it  (Read 11268 times)

Offline VashonKbike

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85 K100RS - Won't start. Starter spins but that's it
« on: October 23, 2015, 06:31:45 PM »
So I had this thing running about 8 months ago.  At least I could ride it around the block but ran out of money to get new tires so it sat.  Now I can't get it started. 

When pressing the start button you can hear what sounds like a fuel pump and the starter spinning (I know the starter was spinning because I took it out and started it and it was clearly spinning).  But when it's back in it spins and nothing else happens.

Tried pushing it and throwing it into first gear, got it to turn over just enough to spit out some exhaust before dying.  Same thing trying to pop it into 2nd.

Any ideas what to do next?  What may be going on? Help!

PS: I started a blog a while back tracking the project I took on with this bike. This was no attempt to do a restore, just trying to keep another K on the road and make a fun bike.  I'm not much of a mechanic either, so it's my practice bike.
https://www.tumblr.com/blog/k100cafe
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Offline Laitch

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #1 on: October 23, 2015, 07:34:57 PM »
If by "spins" is meant that the starter turns the engine over but the engine won't start, then I'd remove that eight-month old fuel and replace it with fresh fuel. After that I'd work my way through the "no start" suggestions on this page.
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  • Along the Ridley in Vermont.
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Offline Scott_

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #2 on: October 23, 2015, 08:02:15 PM »
Sounds like the sprague clutch gear isn't engaging.

Try this....

Put the transmission in 5th gear, while rolling the bike BACKWARDS, engage the clutch. This may/should cause the starter clutch gear to engage the starter gear.

Then give your starter button a try......
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Offline VashonKbike

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #3 on: October 23, 2015, 11:25:46 PM »
Tried the 5th gear trick.  No luck. 

BMW Mechanic friend of a friend said to pull out the starter and check out the gears inside to see if something sticking.  Well it looks like the picture attached.  I stuck my finger in there and could spin those teeth in either direction.  I believe they are only supposed to go one direction?

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Offline rbm

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #4 on: October 24, 2015, 12:07:07 AM »
you're correct; they should only go in one direction.  Pointing to gummed up sprag clutch.
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  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline Chaos

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #5 on: October 24, 2015, 12:08:45 AM »
if the starter is spinning without turning the engine that would be the classic sprague clutch syndrome.  Real pita to get to, but someone posted this a while back and I copied it just in case.  Have not tried it, it involves drilling a hole in the case and spraying cleaner/lube on the offending parts.  Usually happens on bikes that don't get oil changed enough and sit for long time.
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  • sw ohio
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Offline VashonKbike

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #6 on: October 25, 2015, 12:50:56 PM »
Thanks for the tip Chaos.  That's a frightening operation.
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Offline kioolt

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #7 on: October 25, 2015, 01:32:57 PM »
You could try bump starting it.  I've heard that if you can get it heated up it might de-gum the spraque clutch.
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Offline VashonKbike

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #8 on: October 25, 2015, 01:37:26 PM »
I suppose I can drain all the oil, change the filter.  Suck out all the fuel and fill it with some pure non-ethanol gas, some Seafoam and try the bump start.  Hope for the best before I reach for a drill. 
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Offline rbm

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #9 on: October 25, 2015, 03:37:35 PM »
Use a high detergent oil such as used in diesel engines.  Change the oil and filter. Bump start the bike, and ride for several hundred miles if possible.  The detergen should start to break down the gunk that is jamming the sprag clutch and over time it will free up.  Run the diesel oil only until the starter sprag is working, then change to a regular oil.
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  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline VashonKbike

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #10 on: October 26, 2015, 11:00:33 AM »
Robert, that sounds like a good next step.  I'll try it out when things dry up over here.
Thanks to everyone's input!
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Offline VashonKbike

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #11 on: October 30, 2015, 10:20:54 PM »
UPDATE:  So I sucked out all the old fuel, put in some nice, fresh stuff. 

Got a friends who knows what he's doing to come over with some starting Fluid. 

Spayed it in, gave it a nice push out of the garage and popped it into 2nd gear and started it on the first try!  Ran it for a while, the headlight isn't currently working so couldn't take it for a long ride (And the tires still need to be replaced) but when I shut it down it started again without an issue, several times. 

So now on to the electrical.  More posts to follow!  Thanks for everyone's input.
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Offline Brad-Man

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #12 on: October 31, 2015, 08:33:35 AM »
Excellent!
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Offline johnny

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #13 on: October 31, 2015, 08:45:54 AM »
greetings...

engine running butts no headlight... low and high beam im thinking...

its gonna sound whack... butts the bugeye motobrick would run with no headlight... some will say this is impossible... butts when it would happen i would do this and all was well... unless my bulb was bernt out of course...

whack butts true...

j o
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Offline billday

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #14 on: October 31, 2015, 02:39:32 PM »
They say that running synth motor oil  prevents sprag clutch gum-up.
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  • New York State, USA 10977
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Offline Conrad325i

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #15 on: March 12, 2016, 09:39:08 AM »
FYI if you have a sprag thats really really stuck and you cant roll start it due to other problems bc the bike has been sitting for 10 years etc. just do the drill thing.

If you decide to do the drill thing... Drill a little further back than the center of that smooth area. The oil hole for the sprag is more towards the rear of the housing right before it kinda ramps up. If that makes any sense.

Like drill EXACTLY where you see the hole above in that picture. Not in the center of that area
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  • 1986 K75C
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Offline Conrad325i

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Re: 85 K100RS - Won't start. Starter spins but that's it
« Reply #16 on: March 16, 2016, 04:40:47 PM »
Then add a half bottle of seafoam with the oil.

Mine was fixed immediately after a 20min ride.
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  • 1986 K75C
-Isaac
The Hills and Valleys of East Tennessee
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