Hey Everyone

Just got a 1990 k100, first bike and I'm very excited.  Got it for a steal because of high miles but looks mechanically sound.

The question I have is about idling at a light.  It sounds like the engine struggles to stay around 1k RPM and sounds like it might stall.  It hasn't so far but I'm wondering if theres an adjustment I can make.

Clean filters, no clogs, pulls hard through rev range and gets great mileage so far.  There is 1 or 2 SMALL cracks in one of the intake boots but I doubt it goes all the way through.  Thinking of putting some RTV on them to see if it improves.

Very new to bikes and BMWs so any info is appreciated

Thanks!


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There is 1 or 2 SMALL cracks in one of the intake boots but I doubt it goes all the way through.

This is probably your issue.  Easy to test.  At idle spray some starter fluid around the boots between the throttle bodies and the cylinder head. If the idle increases then they're leaking and need to be replaced.

When these cracks are starting, the bike will idle roughly but run fine at higher revs because the vacuum temporarily seals them.

The other thing you can do to smooth out a K is sync the throttle bodies.

http://classickbikes.com/ckb.tech/0.ckb.tech.files/tbsync/tbsync.htm

Thats perfect thanks for the website

Also check the crankcase vent. hose, S shaped, at the rear end of the plenum chamber.

Make sure the rubber blanking caps are on the vacuum take off points on the injectors. Or they may be cracked.
Check the rubber hose on the rearmost take off too.
I once put one of the blanking caps on to an adjuster screw on the TB's by mistake and caused the problem you describe.
I know that at least one other person on the forum has had the same senior moment.

Haha good idea, i think one might be missing...?

Any suggestions for a temporary plug while i order some parts?

Chewing gum? Insulating tape?
As long as it stops air getting in.
Just had a thought. Remember, there are only 3 caps. The rear take off should be covered by a rubber pipe.

A short piece of soft rubber hose with the correct id., bend it 180 degr., add a zip tie.

Thanks for reminding the whole world about my senility Comberjohn. Easy mistake to make really. WEAR YOUR GLASSES.

So that's who it was!
Couldn't remember. Another symptom of impending brain fade.

You are free to speak John he already fessed up.

Finnigan, what sort of 1990 K100 is the bike. It makes quite a difference sometimes, the RS had a 16 valve engine and the LT and Naked had the 8 valve in that year.
Also we find that putting the model and year etc in the signature line helps because you don't need to tell us (see Comberjohn's brainfade post) every time which it is.

Fess up?? It was my confession that made RT come clean.
Anyone else wanna get it off their chest.

Oh maybe I better not laugh too much 

my newly aquired 85 k100rt has kept me busy. i did the clutch spline,driveshaft spline,eng diff fork and trans oil,brake fluid, cleaned every connector and ground, put some rancho gaitors on it. new crank vent hose, new clutch rod boot. synched the throttle bodies but never liked the ROUGH IDLE and hard cold start. changed the injector O rings and that helped. today i replaced the throttle body to head intake rubbers. i have a new bike !!!! the cracks on the old ones could not be seen until out, then if i flexed em i could see the mess. being old and brittle i don't think they seated well up against the head either. my gosh what difference in personality. well worth the time and effort. still a youngster with only 25k.

So now we have another happy customer.
Now off you go into those hills and have heaps of fun 

RicK G wrote:So now we have another happy customer.
Now off you go into those hills and have heaps of fun 

with only 25k  there are heaps of fun left in her....

kartooo wrote:

RicK G wrote:So now we have another happy customer.
Now off you go into those hills and have heaps of fun 

with only 25k  there are heaps of fun left in her....

     

Got into throttle body syncing this weekend:  Found that one vacuum plug was missing, but hooked up my carb vacuum gauges anyway.  All of them seem to be off in one way or another and its impossible to get them all the same so this makes me think its an air leak on one or more boots.  Got it to idle smoother but not near perfect and it had a little trouble -even with chock on- when I first started her up this morning.  Ran to work great though.  Tomorrow I'll get some starter fluid and RTV for a patch job while I save up enough money to get the 50/each rubber boots

Also look at the engine breather hose (tucked up above the TPS between the airbox and the TBs) as it can be cracked causing no end of idle dramas. Another thing to look at is the engine oil filler plug's o-ring. While the engine is idling remove that plug and see what happens. Lightly spray a not-too volatile propellant at the intake boots above and below the TBs to see if the idle RPM changes. This indicates an air leak. The entire airbox system must be tight and leak-free.

BTW, you can only 'sync' the TBs at idle, not running RPM without some expensive, complex kit. Sage advice is to not touch the adjustment screws in the linkage between the TBs.

don't forget the injector seals finnigan  
also a source for air leaks

I couldn't sync my injectors until I checked the valve clearances and replaced three shims.
No problems syncing afterwards.
Might be worth checking if you don't find any air leaks.

Comberjohn wrote:I couldn't sync my injectors...

They're easy to juggle though you must have them out of the fuel rail.
 

Time for a Guinness, I'd say.

replacing the injector O rings did make my idle nicer but no real progress until i replaced the throttle body to head boots. they look good to the eye but once you actually take them out and flex them the cracks really show them selves. carb or brake cleaner with the little tube attached will tell you whats going on.