Hey all, new to forum

I just bought a 1985 bmw k100 (german model), which seems to run great, and smooth, etc etc. I'm coming from a 1968 BSA Lightning that I restored from the frame up, so when I see posts about "unbearable vibration", and the such, I sort of laugh to myself; aka, I really don't know much about what to expect from these bikes, only that they consist of more modern technology and, as such, have a ton more parts. I generally know how things work overall, it's just that with the amount of sensors and computer components that can effect each other, it gets a little overwhelming. Also, I'm not all too knowledgeable about these things on a bike.

Okay, the problems:
1.) Random, intermittent engine cut-out, scary.
-This has only happened to me about 3 or 4 times since I got it about a month ago. I believe it only happens when accelerating, around 4-6k RPM, but the engine will just cut out completely for about a second and then come back without my doing anything. This can be, and is, scary when accelerating in a turn due to the engine braking that occurs. And I'm too busy going "oh crap, oh crap, oh crap" to notice if I still have instrument lights, fuel pump sound, etc.

-Things I have tried:
--tighten up battery connections
--reseat and tighten up the connection to the FI computer
--try heating the Hall Effect Sensor with hair dryer while bike is idling (hair dryer sucked, should probably do again with heat gun)

-Things I have not tried:
--probably a ton of things, honestly no idea where to start, any suggestions or ideas?
--replace ignition switch (ignition switch at the moment has a couple "on" positions, and then if you push it a little farther, more "off positions")
--could it be anything with the ignition computer?
--could it be anything else?? I'm totally stumped on this one... and it's dangerous.





2.) Gas mileage:
-Riding around town, I went through three tanks and got ~105mi per tank... aka, under 19mi / gal. I'm using 91 octane pump gas, all tanks from different stations.

-Things I have tried:
--Make sure each cylinder is firing (started, got it warm, and unplugged each cap from the spark plugs one by one to listen for RPM drop) Passed test.
--Check air filter and air supply connections from intake to air box. (Blew out air filter with compressed air, only a little dust came out, can see light through it, and can feel the compressed air come through it) Put filter back in, it seemed fine. Connections are all good.
--Checked tire pressure (tires were about 8psi low each, pumped up to recommended)
--This problem might relate to #4.

-Things I have not tried
--Freeway mileage. I haven't been on a long freeway ride in order to determine highway mileage, but town mileage is so low, it seems like it wouldn't be a ton better on the highway.
--Valve adjustment (Clymer manual says to have a BMW dealership do it due to special tools ><) I do hear a quiet but easily audible tapping sound from valve side of engine.
--Check in injectors in any way (no idea what to check for / how to check)
--Diagnose FI computer? The guy I bought it from told me he had just recently had the fuel pump changed; could the computer need to be set for a different pump?
--Could it be clogged exhaust? If so, is that just something that I check by pulling the pipes and muffler off and shine a light through them?

-Is there anything else I can check? Some of these things don't seem like they'd cause such a drastic drop in gas mileage from the average of 40-55 i see people claim from these bikes around the web.






3.) Battery Drains when bike is off
-Part of me thinks it's just a dud battery, as I had a brand new battery (maintenance free) on my BSA burp acid all over the bike all the time. New battery fixed it for that bike.
--If I don't ride the k100 for a day or two, it either won't start due to low battery, or starts very roughly / slowly due to low battery.

-Things I have done:
--unplug battery (disconnected positive terminal) while I worked on and painted the bike for a few days (had to bump start bike when I finished, battery had died).
--Ordered a new battery, to be here on July 4-5. I ordered an Odyssey PC925L.






4.) Engine misses at high RPM?
-Not too sure about this one. My brother was riding behind me and told me the bike sounded "sick" (in a bad way), like it was missing at high RPM (around 4-7k)

-Things I have done:
--Tried cleaning inside the spark plug caps (can't think of correct term, but the cords that come from the coils and give power to the plugs) The inside of them look like they have some copper color showing, but are mostly silver / grey colored where the spark plugs would contact.

-I haven't tried anything else






5.) Engine seems to "drop", "lug", and "bog" when I try to grab a small handful of throttle from idle (in neutral).
-I realize it probably has a giant flywheel in it, so I'm not too concerned about this one as that's probably normal behavior, but if not, any idea whats going on?






6.) Noise when letting clutch in, sounds like it's from the clutch area. It sort of sounds and feels like something is "slipping in to place" when I let the clutch in *sometimes*. It doesn't do this all the time. I called the BMW dealership and asked if it needed the splines lubed or anything and said I had no idea when that was last done. The mechanic, who was very knowledgeable and helpful, told me that if I'm coming from a multi plate wet clutch system on a lower power engine (the 1968 BSA set up) and coming in to a single plate dry clutch system on the boxer engine, that's what it will feel like; and that it will feel strange at first, but that it's expected behavior.
-I haven't done anything about this as the mechanic said it was fine, but I figured I'd ask here too as it's not a comforting sound. It doesn't sound "bad", but I suppose I'm just not used to something like that. Any ideas?




Thank you in advance, from the K100 Newbie!!

Hello wellcome, in cca ten years with K 100 1983, only problem I had with cutout was due to o a bad connections under the tank which connects right handlebar switch with el. system. My advice: remove tank check all joints, specially round one that goes to tank on the left underside. With little screwdriver tight every connection and clean it. Secure tank connection with tape. Clean ign. switch, switches on handlebar, check and clean wires under HT leads.

Consumption? The best way is to check engine in some jetronic programe equipped workshop. Its not expensive and you will see everything. My consumption is cca 6 liter/100 km on freeway, in the town could be 7- 8 per 100 km.

My experience with this old (150 tkm) engine: only electrical problem was bad battery, no malfunction on any sensor, computer unit, switch... Once it stopped by cloged fuel filter connected on wrong way for long time.

Usually dirt and corrosion cause only electrical problem.

Safe ride

I have found that one place to check for what you describe is the 4 pin plug connector to the fuel tank. the female receptors often get expanded out of shape and go intermitent O/C also the fuel pumps do seem to have similar behavior when dying.

Check the 4 pin plug that the connectors fit together tightly. Many of the fuel pumps come from used parts and they are just as old as the ones that fail. If you replace the pump get a new one and NOT genuine there are many aftermarket ones for around $50 that are quite good.

I doubt it would be the hall sensor as when they go they don't work till cooled.

Go over every plug connector you can find even under the tank and the earth connectors, one under tank on left side and other just above the coils on the gearbox and remove the starter and clean it and replace the brushes if worn down.

The ignition switch certainly has problems and needs a good one or new. They are notorious for trouble and only have the one key on the ring any more makes the problem worse.

With the rich running have a search on the forum under temperature sensor if they are bad then the computer thinks it is cold and adjusts the mixture to suit.
Check for vacuum leaks around the rubber components of the fuel injection. This system has to be a sealed system from air filter to engine any air getting in except through the air flow sensot will make for bad idle and running.
Use a propane torch unlit and flood the area with the gas, if the idle smooths out there is a leak.
The rubbere under the Throttle Bodies and the ones above and the crankcase vent tube are the prime offenders.

The valve clearances are quite easy to do with the correct tools and need to be right to get a good running K but you should check them to be sure they have some clearance

The battery sounds shot, take it to an auto store as they will load test it for free (thinking a new battery sale is comming their way). If it is shagged get a new sealed one, they are good and charge it before using.

The missing and bogging under throttle could just be the mixture problem.

The clutch problem needs to be seen to.
I think it could be described as a loud clack which I have found to be a diaphram spring/pushrod problem (where they interact is worn) If it is you need to remove the gearbox and do a spline lube as well as check out that noise.

I had a same problem,my engine cut out, I changed the 4 pins connection to the tank(fuel pump & Level sensor). I used a block connection and the problem was solved.

Andy

The thing is, just out of curiosity, I warmed the engine up and, while it was idling, I unplugged the 4-pin connection to the tank. All that happened was the fuel pump shut off (expected). The engine kept idling just the same. I only had it unplugged for a maybe 5 sec before I plugged it back in and then shut the bike off.

Check the switch on the right side of handlebars. Start the engine, move handlebar left and right, move cable, if engine stops......Bad connection on right switch caused cut out on my mike. Simple and easy to fix. Check the ignition switch too.

Regards

nino wrote:Check the switch on the right side of handlebars. Start the engine, move handlebar left and right, move cable, if engine stops......Bad connection on right switch caused cut out on my mike. Simple and easy to fix. Check the ignition switch too.

Regards

If bike was german type you need more octanes. In original manual for that bike gasoline 98 ROZ is needed. I use 98 gasoline

A different octane rating system is used on the other side of the pond
(AKI, anti knock index).........but anyhow still a bit low, 91 AKI ~ 95 RON
good point Nino.

I figured I'd try a couple things today, so here's what happened:

I tested the ohms from the temp sensor on the EFI connection, pin 10, as I've read around the forums. I wasn't sure which one was pin 10, so i counted from each end and tested the according pin (so two pins total)... like this: ---(10)-----(10)--- I tested those ones since I wasn't sure which side to count from.

One started at about 1500 ohms with the bike cold, and dropped to about 200 ohms after about 15min of 4-7k RPM riding. Is this how it's supposed to be, and is there anything else I need to check to make sure the temp sensor is working?

The other initially gave a reading of around 2500 - 4000 or so, but then in under a half second, dropped to nothing on the meter. Same with bike cold and warm.

I also noticed pressure (quiet whining sound) coming from gas tank key hole, as Ive read is how it's supposed to be. I opened the gas tank and it all released in one burst (expected, was making sure I was really hearing tank pressure) Is this normal / expected??

Please have a look at the site's portal, where you will find good fault finding info and where to measure what. (It'll show you where the actual pin 10 is ;-)). It'll also show you a temp/resistance graph.

You have a US bike, which I assume has this flap in the tank to prevent venting off into the atmosphere, so a little bit of pressure build up could be expected (but just that!). Maybe one of our American members with a similar arrangement could comment. The sound you heard was no doubt the fuel pump, which is fitted inside the tank.

Yeah, it has the little spring loaded metal flap in the gas tank. When I opened the tank, the pressure released making the flap.... well... flap around for a second as the pressure passed by it. Bike was off when I did this, so fuel pump was not on.

Some good news here!

So I rode about 85mi on the highway today, and the gas tank is still above half full. It looks like I maybe used 1.5 - 2 gallons, which would put it at 42-56mpg without the full fairing, so doin' good! This tank has quite a bit of injector cleaner in it, and it seems to already be running smoother. Could be my imagination, but it definitely seems to run smoother and better.

Also, I think I *might* have tracked down the random cut-out issue. I think it's the on/off switch on the right side of the handle bars. I've been keeping it in the "other" on position (which I believe is the only on position that's supposed to be there) and it hasn't cut-out in awhile. So I'll probably be looking in to getting a different switch.

Still hearing "grinding" noises from the transmission area at around 4.1k-4.8k RPM, so I'll have to look in to that.

Thanks much, all.

Rabidchiwawa007 wrote:Also, I think I *might* have tracked down the random cut-out issue. I think it's the on/off switch on the right side of the handle bars. I've been keeping it in the "other" on position (which I believe is the only on position that's supposed to be there) and it hasn't cut-out in awhile. So I'll probably be looking in to getting a different switch.

Good to hear that you got progress in the positive direction.

But.... "other" on position....???

Here is a "how to" dismantle and clean the RHS switch assy.

Awesome, thanks Inge!

Yeah, I know the switch is only supposed to have On and Off positions. Right now, it goes a little like this: \ = off | = off, but still on coming from the next position... / = on. and then everything after that, which obviously shouldn't be there, = off

I just need a new switch

From your description it sounds like the contact on the rear side of kill switch knob
has moved a bit out of position.

Should be a easy fix, with aid of the provided link and far cheaper than a new switch.

Cool, thanks for the switch idea, I'll be doing that.

Last thing I'm having happen: I read this elsewhere on the forum, but it said that rear wheel play when in gear should be around 80mm. I just went through all the gears and tested rear wheel play... it's at least a 1/2 inch forward and back (1 inch total movement) in each gear. In first, it's probably more like 1.5 inches. Is this a sign of terribly horrifyingly bad / dying splines?

Thanks in advance.

Rabidchiwawa007 wrote:Cool, thanks for the switch idea, I'll be doing that.

Last thing I'm having happen: I read this elsewhere on the forum, but it said that rear wheel play when in gear should be around 80mm. I just went through all the gears and tested rear wheel play... it's at least a 1/2 inch forward and back (1 inch total movement) in each gear. In first, it's probably more like 1.5 inches. Is this a sign of terribly horrifyingly bad / dying splines?

Thanks in advance.

Quite the reverse actually it means there is very little play in the driveline which indicates very little wear.

Isn`t one inch ~25 mm?............your drive assy seems to be in remarkably good condition.

Hahaha, I suppose I should have checked my conversions before posting

Thanks much