Greetings,

A couple of times lately, my '84 K100RS has started having cold start problems. I mean cold atmospheric - single digits. As I work to 2am and it's winter here in not-always-sunny Queensland, this has been a nuisance, and threatened to be embarrassing at the Mingoola rally a few weeks ago. (out of four bikes, only my girlfriend's '84 K100RS started easily).

It will need to be cranked a few times before catching. Tonight, it just wouldn't catch. At all. I fiddled with the choke lever, used a touch of extra throttle - nothing. Fuel pump was spinning. I am gratified the battery didn't die - I was wondering about that (it's a sealed BMW unit that was in it when I bought it over a year ago now).

Then I tried something I could vaguely remember from Charlie Boorman's Race To Dakar - with the ignition on, slowly open the throttle all the way, then slowly close it, then hit the start button.

It started instantly, barely turning at all before catching.

Then, all the way home, it ran as smoothly and sweetly as it ever has, with no hint of the slight unevenness I've been attributing to dirty injectors needing cleaning.

Excuse me, but: What? Does anybody have any idea what just happened, and why?

Yours in bafflement,
Jonathan

jonathan, I don't know how many times I have said this...it aint a choke, it just opens your throttle slightly. Second, never let the battery get too low or your relay will weld its points together. You can always bump start it if in trouble with a low battery. Does the starter engage OK or does it just spin???Suggest you drain your oil and fill with 5W30 semi synthetic. this will clear a sticky starter clutch. There will be others to help here but give us as much info; as possible. Ajays

amazing ........

ive also had similar start issues recently johnathan .

i attribute it to the cold that we are experiencing just lately ...i find that if i start ....with choke on first notch and a slight amount of throtle opening beyond this ...it catches almost first go and settles back to a slightly lower idle than normal till it warms up a little .
durring the day when the temp is up to at least our normal overnight summer range ...normal operation and starts.

as ajays suggests it could be time for a change in oil durring this unusually early cold period .

Mine is a real Canadian bike and it like the winter time
Colder it is, better it starts.
However, I have to push the starter a bit longer when the temperature is warm or the bike is hot.

I whack the 'cold start lever' to full chat and leave the throttle alone, then press the starter button and she fires and runs immediately without assistance from the throttle. I close the 'cold start lever' to its halfway detent and let the bike warm up slightly (at about 1200-1300 rpm on that setting) for as long as it takes to pull on my gloves, then just as I'm riding away I close the 'cold start lever' fully. A strong battery helps. Like CF's, my bike has to crank a bit longer in order to fire when it's warm. (Edit: This technique I only use when the air or the bike is cold. I never have to use the 'cold start lever' above a certain ambient temperature or when the bike is warm).

Once I ran for 1,000 ks on diesel oil, mine started much more reliably, although I have now done about 3,000 on normal oil and am noticing a reluctance to engage first go. Time to do it again methinks.
RT

As Bert said the choke lever is a fast idle but also when you open it fully that is the self return bit it is supposed to give a super rich mixture for cold start.
The lever has two distinct operations one is the first part which gives fast idle and the second as you push and have to hold it there will or should give a very rich mixture.

If you are having trouble starting in moderate cold then check the temperature sensor for correct readings.

My K100 and K75 both start with no choke and no throttle. The K100 loses pressure in the fuel rail quickly and so needs priming and that is done by a tap on the starter button so the pump runs then press the starter button and bang she fires where the K75 holds pressure for days and usually starts on the first firing stroke. With any of the bosch L Jetronic or the later Motronic Fuel injection holding a bit of throttle above what the choke lever gives (which is very little) causes the system to override the signal the temp sensor gives the ECU for cold start. All the manufacturers that use Bosch EFI say DO NOT TOUCH THE THROTTLE WHEN STARTING in the owners hand book. Apparently even operating it and releasing it once after the ignition is turned on will cause problems.

The cold start part of the choke lever should only be needed in extreme cold ie below freezing.

I havent got my copy of the bible on Bosch EFI (written by Bosch) as I lent it to a friend and havn't got it back yet but from memory that is the gist of it.

I won't say that it is always like that but that is the way it is designed.

ah !!!.....good thoughts ....must try that ....i thought there was something wrong with mine and was looking for a second detent in the choke mechanism ...but i could only find the first one.

so....hold the choke fully open when starting ... or prime the fuel rail with a quick start button press first .

good work, thanks for the update guys

always learning here

Alrighty then:

Oil is fresh plus less than 1,000km.
Starter clutch is engaging and cranking the engine just fine.
Yes, I was aware it's not a choke, but it's a convenient short-hand.

The thing is, this was a completely new phenomenon, and what baffles me is that slowly opening and closing the throttle with ignition on but the starter not engaged should then give instant start.

I don't usually need any of the cold start lever to start, but lately I think the injectors have been getting a bit gummed and it needs some help. May not be the injectors, of course. I find it runs better if I idle with the lever engaged for as little time as possible - gumming the injectors, perhaps?

In other threads, people have said BMW advise against letting it idle to warm up at all, just ride and be gentle until it's happy to rev. I find that results in better running.

Nobody has any ideas about the slow throttle twist, then?

Jhepburn wrote:Alrighty then: Nobody has any ideas about the slow throttle twist, then?

Charlie B wasn't likely on a 25 year-old K bike at the time. Carbies? Modern fuel injection? I'd stick with what K Freak mentions about the Bosch EFI manuals recommending no throttle AT ALL when starting from cold temps. I think we're all slightly tempted to prime it a bit as though there's some magic enrichment device like a pumper carbie in the days of old. But this does nothing on our bikes. Perhaps you're right about cleaning the injectors, but of course how is the rest of the system as far as its state of tune? Valve clearances within specs, ignition timing spot on, air filter and fuel filter cleanliness good, sparkies gapped correctly and clean, oil of sufficiently 'thin' viscosity, and etc? Winter and the accompanying colder temps do highlight weaknesses. I know my bones feel a tad more brittle and I am more likely to wanna tuck up under a thicker doona.

Two Wheels Better wrote:Charlie B wasn't likely on a 25 year-old K bike at the time.

Yes, you're missing the point there was a distinct difference.

I serviced it less than 1,000 km ago - air, fuel, oil filters all good, plugs new and gapped correctly, injector state is only a supposition, I went to a slightly thinner oil.

I am familiar with engines, including this one, that start reluctantly and need a bit of coaxing, and the way it behaved last night was distinctly different - after failing to even catch, it started instantly and well after twisting the throttle open and shut.

I'll keep looking for possibilities.

jonathan,
I use an additive in the petrol to clean the injectors on occasion. Sounds as though you know what you're at and no novice.
Ajays

No point missed, mate. Like everyone here does, as a part of a dialogue in an attempt to narrow things down a bit, I'm merely trying to deduce what I can about your unique situation. You've given us a bit more useful information to mull over. Now let's see what the collective can come up with for you.

the only thing that i could think of ....was by opening the throttle and then closing it was .....to activate the tps switch from open / closed states ....whilst the ignition being on the efi computer may see this as a change state ......

i noticed after deactivating my tps ( much smoother round the twisties and especially down hills ) i have this tendency to not start so well ...

i wonder if the tps switch is a state read by the system.....and if yours is gumming up johnathan ?

just a thought

you never know ...

So:

I've put a cleaning additive in the petrol - do so occasionally - but it's in the current tank so I'm not sure if it's having an effect, or even if it's dislodging something that clogs an injector until it can be dissolved by more additive.

I asked a friend who develops EFI systems for a living about using injector cleaners or about pulling and cleaning them properly and his response was "Yes, well, um, it might help, if that's actually your problem."

The TPS possibility interests me. I've had problems with mine getting wet - not the switch body itself, which is thoroughly sealed, but the connector on top. As a consequence, I now keep a small can of WD40 under the seat (I have no room under my seat any more, with all the extra tools, tape, rags and 1st Aid Kit I carry as standard).

I haven't tried disconnecting it to see what would happen, but my understanding is that it assists with starting and it assists with smoothing out throttle response down low, so I am reluctant to try disconnecting it. I may have to clean and seal the terminals again and see if that changes anything - they were quite corroded before I cleaned them the first time I got the old TPS no-revs problem.

The one thing I don't like about the K is that it's old but very electrical. I understand electrics least, so I'm happier with either carburetors or a more modern bike with an extra decade of development and testing experience behind it.

Jonathan,
TPS is much better without the 1st switch stage, My bikes are set so the first click doesn't function but it still has the top end fully active. I can assure you that this setting gives better handling. You may experience a poping in the silencer on closed position now and then but much better.
As Charlie says, try disconnecting the plug and feel the difference.
Ajays

johnathan .....wd 40 is great ...but for cleaning electrical issues ...(mainly connectors ) there is nothing i have experienced with better effect than "deoxit"

basically, as you would know the tps is a micro switch ...and that type of switch can often become contaminated ....usually the actuall contacts start to corrode ..(as small fragments can enter the switch via the button mechanism) but more likely the contacts of the joining connectors may well corrode ...i have found that by useing this stuff ..many probelmatic issues have dissapeared ...(speedo sensor ...etc )

the tps activity/signalling whilst great for sure ....does make the change from 2000 and above revs down (throttle closed ) a bit severe for me ....and at the suggestion from ajays and many others ....i have mooved the position of it ... so that its still there ...but not active on throttle closure (by rotating it slightly anti clockwise in relation to the shaft ) but not disconnected it .

im sure that it was installed to comply with emmissions laws and trends...but there are other reasons for it as well .....i just chose to ignore that at the moment ....grin...

charlie99 wrote:johnathan .....wd 40 is great ...but for cleaning electrical issues ...(mainly connectors ) there is nothing i have experienced with better effect than "deoxit"

basically, as you would know the tps is a micro switch ...and that type of switch can often become contaminated ....usually the actuall contacts start to corrode ..(as small fragments can enter the switch via the button mechanism) but more likely the contacts of the joining connectors may well corrode ...i have found that by useing this stuff ..many probelmatic issues have dissapeared ...(speedo sensor ...etc )

the tps activity/signalling whilst great for sure ....does make the change from 2000 and above revs down (throttle closed ) a bit severe for me ....and at the suggestion from ajays and many others ....i have mooved the position of it ... so that its still there ...but not active on throttle closure (by rotating it slightly anti clockwise in relation to the shaft ) but not disconnected it .

im sure that it was installed to comply with emmissions laws and trends...but there are other reasons for it as well .....i just chose to ignore that at the moment ....grin...

Deoxit, eh? Haven't heard of that, may have to give it a go. I've had to pull my instrument panel apart and clean and check the connections, and I now need to get a friend of mine to weld a solder back in place to restore my speedometer (yes, it really is down to that one wire, I am very sure of that!) so, given the age of the bike, the fact I'm only the second owner to actually care for it, and other issues, I may have to investigate this Deoxit of which you speak.

I may also have to play with the TPS a little. I haven't had any problem with a 2,000 RPM transition while the engine is running sweetly, but then I don't usually go that low anyway.

One thing I keep meaning to try but haven't is to just plain disconnect the TPS and see if it makes the slightest difference.

try a trip up and down nebo johnathan.....after and before

whilst cruising along the highways its not quite as evident ..... in fact the braking effect is good ....no ?

try jaycar for the deoxit ...i bought the two pack bottles version youll see what i mean.... if you read the instructions

good luck !!!!

My two cents worth...

DeoxIT...like Charlie said, doesn't just clean the contacts, it "coats" them as well, reducing/eliminating further corrosion. The ProGold stuff is for brand new connectors that are gold "flashed". Not much cleaning agent in that. There's more cleaning agent in the Power Booster stuff.
The aerosol cans have saved me from pulling apart switchblocks and brake light switches. Yep, I'm lazy...

Jaycar, everywhere in Bris Vegas.

Got a quiet Saturday arvo? Use it on every connection on the bike. Pull all of the connections, bulbs, relays, switches, dodadds and thingos.

If I had this stuff when I had my Ducati 860, I would have been a happier man back then!

I'm a bit of a fan of JayCar, have to make another visit, obviously!

I've seen that BMW recommend a complete disconnect-WD40-reconnect of every electrical connector every 6 months (I think it was 6 months) and I am steeling myself for that coming up. I've got a quiet fortnight work-wise coming up. I may have to do a full clean and DeoxIt session.

Incidentally, I had a problem with my right rear indicator being intermittent - I pulled it apart and found epoxy sticking the bulb into the connector. WTF? I cleaned the epoxy off, found no cracks, breaks or loose fittings, put the same bulb back in and now the indicator is fine. I keep finding little things like that which make me wonder about previous owners.

That's what I hate about buying used bikes...what was the previous owner(s) thinking?

Speaking from experience, forget the WD40 trip...really. Use DeoxIT. You may need to do it again in twelve months, not six.

I also love Jaycar.

First of all - never mind how it works, on the cover BMW calls the lever 'choke' and as we are here to help each other lets make sure we call it what the makers have called it. There's already confusion enough. The TPS has various functions dependend on to operations mode of the bike. It allows some enrichment for starting the bike and switches off the injection if the throttle is closed until the engine is below 2000 rpm (and therefore allow full braking on the engine which some find uncomfortable). At full open it again enriches the mixture for full power and preventing a too lean mixture. There is no link between the choke and the ECU so there is no enrichment resulting from a choke position. The choke opens the throttle shaft; have a look what it does while you look at the throttle bodies. If you need to keep the throttle open in order to be able to start the bike you need to look at the adjustment/setting of the various parts, as it should not be necessary.

I agree that it is mildly pedantic to fret over what the lever is called, and what it says its function is, but reckon most here are simply making an attempt to clue others in about what the lever actually does (which is not a choke at all) as all of us have now done in some fine detail.

The point is in understanding what is happening when we flip that handy little lever labelled 'choke'.

BTW, the very same part is fitted to the left hand controls of '80s-era onward Airheads which do have a choke - it's BMW's shared parts bin engineering.

I hope we all appreciate that not all are BEng or higher qualified to appreciate the idiosyncrasies of the actual working of the thing. It's not really important to solving any real issues with the bikes.

Of course, the whole debate over what to call it is made infinitely more entertaining by the realisation that, in my experience, very few people actually know what a choke even *does* (in the wider community, of course, I'm sure we're all more knowledgeable in here).

And, completely sideways, I *like* BMW's shared parts bin engineering. It gives a sense of continuity and familiarity, and makes parts easier to find.

And I thought I was giving info; to a newbee in newbee language. Sorry chaps, keep it lighthearted. And Renez, I most certainly respect your knowledge and have benefitted from it in the past as so of others. Have a good day.
Ajays

Sounds as though you know what you're at and no novice

Ajays, I wasn't having a dig at you, I really value your posts. I'm on various forum and it seems that every post where choke is mentioned people feel the need to go to great length to explain that the handle shouldn't be named a choke, whilst most don't know at all what a real choke does. There is no information as they all jump at the word, but no one explains the difference/actual working of a choke. The reason it irritates me somewhat is that most posters do not know enough about engine mechanics to understand it and might feel uncomfortable asking further questions if we get picky about 'proper language' or make them feel stupid for not speaking 'our' language. It says choke on the cap so that is what they will call it.
And yes, I feel a lot better now

cheers rene

Folks RFI (request further information)...concerning riding the bike tomorrow to a 15k away hiking gig at a local park.  My truck is down for a day or two.

Rode the bike yesterday at 0/C 32/F and all was well.

Bike is kept outside....(I know and am working on renting a shed because Santa might be bringing me an '88 RT)...

Temp is now -7/C 19/F and went outside to see if it would fire.
Fired happily up.!!!  Then started thinking that I might be doing it harm because it has 10w40 in it now and turned it off to come inside and see what our mob has to say on the issue...

My plan is to go ahead with the ride in the morning....but to be kind to the bike shall at least put a light bulb under the tarp near the motor....?

And the rider has considerable climbing/winter camping/military winter survival experience...Alaska...etc....so that is not a problem...probably....

Await and appreciate thoughts on the matter.
Thanks.

Well acording to BMW that temp and oil is fine

Thanks Rick.
Am good to go.

perhaps the globe under the sump jim ?

Worked just fine Charlie thanks.
Now the rider needs to get some warmer gear!