Trying to revive a sleeping bike

[Swampyankee]

I'm trying to sort out an start my "new" 86 K100RS.  Got a new battery, resealed the leaking fuel level sender port, went repaired broken wires to temp sensor, and pulled fuel pump and bench tested it with success.

The tank had very little gas in it and presumably old so I put a couple gallons of fresh gas in it.
After much cranking over it would try to start and eventually got running but wouldn't idle. Then would no longer start. I noticed fuel dripping and traced it to the low point of rearmost header pipe. Felt around and thd pipe is dented and perforated, probably rusted thru. I pulled the plugs and they all were wet. I dried them and checked and got spark. Reinstalled them, but the bike is not starting.

Any tricks to bringing an old K100 back from the dead? Or is there something amiss I should be looking for?

[daveson]

Just to pick up on your comment about fuel dripping from the rear header pipe. The fuel pressure regulator is connected to the rear cylinder by a vacuum hose. The regulator might be leaking, and fuel getting to the cylinder from the vacuum hose. Crank it then pull the hose from the throttle body at cylinder four, if it's damp or has signs of fuel, the regulator is leaking and needs to be replaced.

If it was a small leak and not noticed by the previous owner, the sump oil level could rise over time as it gets contaminated with fuel. That's one reason the oil level wants to be below the top of the sight level glass. If it was a big leak, it could be even worse, like hydraulic lock bending a con rod.

[Swampyankee]

I can check that but I had that hose off - it doesn't have a relly tight connection - and it was dry at the time. I checked because after running but not being able to idle i looked at the vacuum taps on all 4 throttle bodies and 2 were open. Not having the proper plugs, I improvised with short pieces of tubing with a screw plugging the end. Classic shadetree mechanic bodge, I know.
Now that I mentioned that, it was after that "repair" that I couldn't get it started again.

[daveson]

The hose might be dry if it wasn't started for a while. The hose and plugs want to be tight. Check that the vacuum hose is connected to the pressure regulator. Check also the hose for leaks between the plenum chamber and engine case.

It might be running rich on all cylinders, and run better temporarily with the fuel pump unplugged.

[Swampyankee]

I looked for the regulator thinking it was the reason for the gas leak but couldn't locate it. I need to invest in a manual. Where does the regulator reside?

[Laitch]

I need to invest in a manual. Where does the regulator reside?

There's a downloadable BMW Repair Manual in the Service Manual section of this site. That will be cost free.    The fuel pressure regulator is behind the throttle bodies. See Chapter 13, p13.

[frankenduck]

I looked for the regulator thinking it was the reason for the gas leak but couldn't locate it. I need to invest in a manual. Where does the regulator reside?

The Fuel pressure regulator (FPR) is located on the back of the throttle bodies.



You need to remove the airbox to access it.

How to:
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/k75pa.rehab/k75parehab.htm#fuelair

Note that you don't need to take the mass airflow sensor out of the top of the airbox if you're just trying to get to  the FPR.

[Swampyankee]

I attempted to remove the air box just to trace the fuel return line looking for leaks. I couldn't get the intake air plenum off the airbox before I ran out of time. Gotta get back to it.

[Swampyankee]

I failed to mention that this bike probably had not been started in at least a year. Battery was flat dead and wouldn't take a charge. It also looks like it had been left outside for an undetermined amount of time.

I'm out of town for the rest of the week but I hope to look at it again next weekend.

[TommyT]

You wrote: "The tank had very little gas in it and presumably old so I put a couple gallons of fresh gas in it."

Did you get the ALL of the old gas out before you added your fresh gas? In my past experience just a little bit of old gas in a MC gas tank will not mix well with fresh gas and will make any bike a no start or not run much above an idle. 

[Swampyankee]

Back at it after a week away. I drained the tank and got out over a gallon of amber colored fuel and about 4 oz of water.
 
20221113_132739.jpg (47.65 kB . 768x576 - viewed 378 times)
I mopped out the tank as dry as I could and added some fresh gas.
After alot of turning over and purging the filter and lines I managed to start it but no better than my first attempt, and as before it would not idle nor restart. Gas is draining from the exgaust via the pinholes in the low point of number 4 header pipe. I'm beginning to suspect the injectors so i pulled them and they don't look great externally.

20221113_132708.jpg (55.29 kB . 768x576 - viewed 405 times)
Is there a way to test them and clean them, or am I better off just replacing?

[frankenduck]

Whenever I get a "new to me" K bike I send the injectors to:

https://www.mrinjector.us/

He'll not only recondition them but also repaint them. I've sent him some really beat up injectors before and they came back not only working great but also looking great.


I got a K100 once that had been sitting under a tarp in Seattle rainy for so long that the water had separated from the gas.

[Swampyankee]

Whenever I get a "new to me" K bike I send the injectors to:

https://www.mrinjector.us/

He'll not only recondition them but also repaint them. I've sent him some really beat up injectors before and they came back not only working great but also looking great.


I got a K100 once that had been sitting under a tarp in Seattle rainy for so long that the water had separated from the gas.

Thanx for the referral. For what its worth I just went ahead and ordered a set from Mr Injector.
BTW, the bike you mentioned sounds alot like the condition I got mine in. Lots of weather on frame and alloy parts.

[Swampyankee]

Got the new injectors installed but motor is not any better. After much cranking with fuel pump plugged in as well as unplugged with a few pops and false starts, i pulled the plugs and tried the oil in the cylinders trick to no avail. Plugs are quite sooted up so I cleaned the electrodes with a bit of sandpaper. Got it to run for a bit but it died. Thinking it may be just out of gas I put 3 gallons of hi test in it, plus i hit it with some starter fluid. That seemed to do the trick and it ran for maybe 5 minutes and eventually settled into a rough idle but would pop and crackle with black smoke when revved as if it were running rich. I experimented with pulling the caps of the vacuum tubes and then sprayed the intake boots with carb cleaner looking for a leak. At that point it died and would not start even with shots of ether. I pulled plugs and found weak or no spark at the plugs, although I could feel the voltage even through the insulated handle of the pliers holding the plug when i lifted it from grounding on the block.

At this point I'm completely miffed. Maybe this is the real reason the PO was selling it, even if he did play up the saying goodbye to an old friend bit.
I will get some new plugs and see if that would improve the sparkulation. Any other suggestions??

[frankenduck]

Here's a good K100 troubleshooting write-up by the frog over at the K100 forum.

http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/k100tshoot/K100.Troubleshoot.Start.2018.pdf

First things I would check:

Resistance across ignition coils. Page 15


Also check the water temp sensor resistance between L-Jet pin 10 and ground.
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/tempsensor/tempsensor.htm

[The Mighty Gryphon]

What kind of spark plugs are in it?  NGK D7EA are pretty common and work well, BUT they need the terminal nut on the end to make a good connection to the BMW plug wires.  If you use them, and many of us do, get the nuts.  I have got them from a shop that repairs lawn mowers.  They will often have a bucket of old Briggs and Stratton plugs that you can get a few nuts from.  Another source is to contact NGK USA tech service and ask.  A few years back I got a dozen from them no charge.   

[frankenduck]

There's a good chance that your crank case breather hose is shot and needs to be replaced.

http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/ccb/ccb.htm

[Swampyankee]

What kind of spark plugs are in it?  NGK D7EA are pretty common and work well, BUT they need the terminal nut on the end to make a good connection to the BMW plug

The plugs are Bosch but I did not take note of the type. They do have the caps on them.

[Swampyankee]

There's a good chance that your crank case breather hose is shot and needs to be replaced.

http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/ccb/ccb.htm

I can check that but explain how that contributes to a no start or hard start condition. I should mention again that gas  is overflowing a enough that it dumps out the exhaust. Of course the only reason I know is it drips out of the pinholes in number 4 cylinder header pipe.

[frankenduck]

I can check that but explain how that contributes to a no start or hard start condition. I should mention again that gas  is overflowing a enough that it dumps out the exhaust. Of course the only reason I know is it drips out of the pinholes in number 4 cylinder header pipe.

If you're over-fueling that much then my first suspect would be to check the water temp sensor resistance that I referred to above.

[Swampyankee]

I believe one of the things the PO was something about the fan relay, which could be more akin to a temp sensor malfunction.  But you also need to elaborate on the crankcase breather hose comment.

[Laitch]

You've indicated there is fuel excessive enough that it dumps into the exhaust system. Why?

1)The crankcase breather hose is allowing so much unmetered air into the system that the mixture is too lean to ignite and injected fuel is not consumed and dumped into the exhaust system.
2)There might not be enough air in the mixture to permit combustion.The air snorkel could be clogged or the air filter could be clogged. The fuel mixture is too rich to ignite; fuel is dumped into the exhaust system.
3)The coils might be damaged so not providing hot sufficient spark for ignition to consume fuel.
4)The primary coil wires might be loose or corroded so the coils cannot supply sufficient spark to ignite the fuel.
5)The plug wires might be degraded enough that they cannot provide sufficient energy spark for ignition so fuel isn't consumed.
6)Degraded throttle body connections are leaking unmetered air into the system so the fuel mixture is too lean to ignite.

All the un-ignited fuel is being dumped into the exhaust system.

[Swampyankee]

Thanx for the explanation. I will investigate. One supporting thing to note is that it runs better with all the vacuum plugs removed from the throttle bodies.
One thing to add - when i pointed out a pair of wires with bare ends the PO said he thought they had been chewed through by a rodent. I traced them to the temp sensor at the bottom of the radiator. I pulled the connector and soldered the wires back together and heat shrink tubed over the splices. But it looked like the mouse had done a very clean job of cutting and stripping the wire ends... think. The other thing was the pair of wires were the same colors - purple and yellow IIRC. Since I couldn't tell them apart I assumed it didn't matter which went where. Am I wrong there??

[frankenduck]

Unlike many temp sensors that have a temp sensor wire and a ground wire, the K100/K75 temp sensor is a dual temp sensor that grounds to the threads it's screwed into and has "outputs" to both the temp relay and the L-Jetronic. That's why both wires are the same color (violet/green) and they should output the same resistance.

[Swampyankee]

So I need to check resistance to ground at both contacts in the temp sender. Good to know. I'm piecing together my understanding of the operating system on this bike. Let's hope I don't screw things up too badly before I get it figured out and running. Although for what I paid and the condition this thing is in, it's probably not a bad bike to learn on. The more I work on this thing, the more discouraged I am with the work needed to restore/renovate. The bike really is pretty ratty, with rusted rear frame section, bad paint on bodywork, etc. I may end up getting it running and then sell it as a good candidate for a cafe/rat/brat bike conversion, and find a better example for running in original condition.