1. Here's the big one. It won't start when the bike is hot. The starter is turning the engine. The fuel pump is pumping. But it doesn't start. I can think of lots of things that would cause that, but most of them would also cause the bike to run badly. Before I shut it down the bike was running GREAT. Smooth solid idle, up to tons of power at high RPM, and everything in between. It seemed to run perfectly until I shut it down, and then 20 seconds later it would not start. I tried just starter, starter with a bit of throttle, a lot of throttle, some choke, full choke. Nothing. And it starts instantly when cold. The only thing I can think of is vapor lock. It is winter gas and I did get the bike pretty darn hot. Do Ks even suffer from vapor lock? What else could it be?
   
2. The rear shock is leaking BADLY. I don't need any help with this issue. Just sympathy. The shock is already in the hands of UPS on its way to Works Performance. They say they'll need it for 3-4 weeks.  
   
3. The engine got quite hot while I was riding. I suspect this isn't a problem. I've heard the Ks get pretty hot. And it reached a hot temperature and then just stayed there. It cooled down on long descents. I feel pretty sure that it was normal. I'm just wondering how to differentiate between normal hot and problem hot. Does the temperature light on the dash light up for too hot in addition to cold? If the engine was too hot, could that have caused issue #1?
   
4. Is my battery charging? While I was trying to start the bike as described in issue #1, I noticed that over the course of a dozen attempts to start the bike the starter sounded noticeably less emphatic. Is that normal? Should a battery be able to power minutes of starting attempts without diminishment? How can I check that the battery is charging while riding? The battery light turned off while the bike was running. Is that a solid indication that everything is okay? Or could I still be having alternator/charging issues even if the light turns off?
   

Bikesmith wrote:Hi everyone!
    Well, I got my bike running. It's a 1985 K100rs that my wife gave me for my birthday. I spent the last three weeks getting it running. Hall sensor, fuel pump, bad wiring connections, relays, tires, switches, final drive splines. I've been all over that thing.
    So I got it running a couple days ago. The first couple of rides revealed a new batch of problems and questions:

1. Here's the big one. It won't start when the bike is hot. The starter is turning the engine. The fuel pump is pumping. But it doesn't start. I can think of lots of things that would cause that, but most of them would also cause the bike to run badly. Before I shut it down the bike was running GREAT. Smooth solid idle, up to tons of power at high RPM, and everything in between. It seemed to run perfectly until I shut it down, and then 20 seconds later it would not start. I tried just starter, starter with a bit of throttle, a lot of throttle, some choke, full choke. Nothing. And it starts instantly when cold. The only thing I can think of is vapor lock. It is winter gas and I did get the bike pretty darn hot. Do Ks even suffer from vapor lock? What else could it be?
   If the engine over heats it will keep running but if stopped it will not restart until the temp falls to within the operating range because the FICU disables the start circuit. So, one of two possibilities. Your engine is over heating or the Temp sensor is kaput and gone closed circuit. First test the resistance between pin #10 and #13 on the FICU plug. When cold should be 2.5KΩ @20 ̊C. Then test when the engine has over heated (won't restart). Should be around >200Ω. If it's zero the sensor will be dud.
   If the sensor is ok, your engine could be overheating. Valves, air leak, coolant obstruction (thermostat), fan not working. Have you removed/tested the thermostat?
   
2. The rear shock is leaking BADLY. I don't need any help with this issue. Just sympathy. The shock is already in the hands of UPS on its way to Works Performance. They say they'll need it for 3-4 weeks. Bugger.
   
3. The engine got quite hot while I was riding. I suspect this isn't a problem. I've heard the Ks get pretty hot. And it reached a hot temperature and then just stayed there. It cooled down on long descents. I feel pretty sure that it was normal. I'm just wondering how to differentiate between normal hot and problem hot. Does the temperature light on the dash light up for too hot in addition to cold? If the engine was too hot, could that have caused issue #1?...Yes. If the engine is actually overheating the FICU will prevent restart
   The temp warning lamp lights up when too hot. Mine has never come on except for initial ignition/engine not running.
   
4. Is my battery charging? While I was trying to start the bike as described in issue #1, I noticed that over the course of a dozen attempts to start the bike the starter sounded noticeably less emphatic. Is that normal? Should a battery be able to power minutes of starting attempts without diminishment? How can I check that the battery is charging while riding? The battery light turned off while the bike was running. Is that a solid indication that everything is okay? Or could I still be having alternator/charging issues even if the light turns off? Not a good idea to keep turning the starter over too much. If your battery sounds like its getting tired put it on the charger.
   To check the alternator voltage output just measure the voltage across the battery terminals at >2000rpm. If voltage drops while riding, the charge warning lamp will light up.
   

   Other than those things, the bike ran INCREDIBLY. The engine sounded so, so smooth. Man, what a fun bike. I can't wait to take it out again (I don't suppose anyone in the Boulder, CO area has a rear shock I could borrow for a few weeks?).
   Thanks, as always, for all your help! This community is fantastic!

Bikesmith wrote:From Kaptain Holister:
If the engine over heats it will keep running but if stopped it will not restart until the temp falls to within the operating range because the FICU disables the start circuit. So, one of two possibilities. Your engine is over heating or the Temp sensor is kaput and gone closed circuit. First test the resistance between pin #10 and #13 on the FICU plug. When cold should be 2.5KΩ @20 ̊C. Then test when the engine has over heated (won't restart). Should be around >200Ω. If it's zero the sensor will be dud.
If the sensor is ok, your engine could be overheating. Valves, air leak, coolant obstruction (thermostat), fan not working. Have you removed/tested the thermostat?

I haven't done anything about this issue yet. Is there a way to check the temp sensor without the bike running? With no rear shock, it'd be tricky to get the bike hot. Can I just put the sensor in hot water? Can I do the same with the thermostat? It seems that the sensor being faulty might explain why I'm not getting a temperature warning light. Am I correct in thinking that?... not sure about that. The feed for the temp warning light comes from the temperature controler in the electrical box and the controller is on a different circuit off the sensor (it has two connections plus the earth body). I'm on the road atm and away from my resourses so maybe someone else can chime in on that.
You can test the sensor in hot water but you'll only get it to 100 ̊C. Engine can get a little higher than that under pressure. I can't remember what temp it cuts the starter circuit. Anybody?? The temp sensor is a little difficult to remove anyway.
Just run the motor for 10 to 15 mins at idle with a little choke to get her up to operating temp and see where you get to from there. Switch her off and try to restart. Have a few attempts. Measure the pins on the FICU plug.
Remove the thermostat and stick it in a sausepan on the stove with a themometer and see what temp it opens at. The manual will have the service specs for that. I can't remember and I'm on the road atm.

If the engine is actually overheating the FICU will prevent restart
The temp warning lamp lights up when too hot. Mine has never come on except for initial ignition/engine not running.

My temperature light is on when I first turn on the ignition, then goes off shortly after I start the bike. It never came on after that.
That's how it works

Not a good idea to keep turning the starter over too much. If your battery sounds like its getting tired put it on the charger.
To check the alternator voltage output just measure the voltage across the battery terminals at >2000rpm. If voltage drops while riding, the charge warning lamp will light up.

I know. I don't like stressing the starter. I wasn't running it continuously. Just a few seconds at a time, with 10-20 seconds break between attempts. So, checking the voltage across battery terminals: what will I expect to see if all is well, and what will I expect to see if there's a problem?
13.6V to 14.4V. Typically around 14.0V. Things that will affect the alternator output voltage will be the voltage regulator. Remove from the back of the alternator, check the length of the brushes (refer to manual for service specs), give it a clean, replace. Try cleaning the alternator connector. Good earth connections are needed for the charge to get to the battery terminals. If voltage is sustantially lower the rectifier diodes are probably gone.

Thanks so much!

Motorbike Mike wrote:I hadn't used thread tape and all is well.

Ooooh you guys!

Bikesmith wrote:.....
Every few minutes I would shut it down, check the resistance from the temp sensor at the FICU, and then try to start it up again. Initial resistance reading (cold) was 2.5K, then .93K, then .56K, then .33K. Seems normal, right? The bike started instantly each time.
   It really seems like everything is working fine. The fan never came on, but I wouldn't expect it to.

......

Kaptain Holister wrote:The readings look good. Did you put the new one in or put back the old sensor?
If you leave your enginge idling for about 10 to 15 mins while stationary the fan should come on. If it doesn't, I'd check out the Temperature Controler (the fan's been replaced, the sensor checks out).
If your engine IS overheating, that could be difficult to track down.... so many possibilities. Look to valve clearances, air leaks etc. What do your spark plugs look like?

Cheers

Bikesmith - #21 wrote: I left the old sensor in. Since it was reading perfect, there didn't seem to be any reason to pull it. I removed the connector and cleaned the contacts.

Bikesmith wrote:Post #17
Next issue: The battery. As a couple of you suggested, I checked voltage at the battery while the bike was running. At 2000 RPM, I'm getting about 13.3 volts across the terminals, which seems to be lower than you've said I should see. I was mostly seeing the same voltage when I revved even higher, except for one time when the voltage dropped to about 12.5 (fluctuating) at 3000 RPM. That time, though, could have been just because of my inability to hold the meter leads steady. Mostly it was staying at right about 13.3 no matter how high I revved. But overall, it seems low. Is it problematically low? If so, what's my next step for addressing that?
Post #21
Any thoughts about the alternator situation? My gut feeling is that my battery is giving out. It strikes me as weak even after being freshly charged. the best I can get in a static test is just a touch over 12 volts. If the battery is going, would that give me a low voltage reading at 2000rpm?

Bikesmith wrote:.........

A couple questions about the battery/alternator issue:
   First, The Clymer manual says that at 2000rpm, any reading between 13 and 14 volts is fine. Is that wrong? Does it definitely need to be at least 13.6? Yes.   You'll see 13-14V across the interweb on various sites but its not correct and I'm surprised to see that in the Clymers manual. For a standard automotive battery/charging system like we have on our Ks, the alternator output has to be 13.6V to 14.4V. Below that and the battery will begin to discharge as it's used for starting etc. Once it cycles down to empty the battery plates will be damaged and the bat will never be the same again. Over 14.4V and the battery begins to out gas hydrogen. That will eventually lead to a damaged battery but is also potentially dangerous. At 14.6V the electrolyte will begin to boil. Around 14.0V is the norm. My alternator is consistently on 13.9V at 2k rpm. My static battery charge (after a good rest) is always 12.9V. I never need to use a charger to top up but I ride most days. I have an AGM battery
   Second, my battery seems only borderline. Fresh off the charger, it's putting out only 12.1 volts. Could that be the only problem? Could a bad(ish) battery explain the low charging voltage? No.  The exact opposte. The low charging voltage from the alternator explains the bad battery. 12.1V is not "badish"... it's practically dead. A 12V (nominal) battery is considered empty at 75% charge which is 12.45V. Below that the battery begins to sulphinate leading to rapid degradation. At 12.1 your battery has 25% charge and is damaged. That's why it won't hold a charge. If you use the battery in this state to crank the motor you run a good risk of frying your starter relay. Very common.
Sounds like the votage regulator is kaput which has led to a damaged battery. The VR is reasonably cheap. I posted a link in my previous post. Replace the battery with something like a 25Ah AGM type for trouble free electrics. There are quite a few recent posts on the forum about battery selection.
  
   -Jon