Hi all,

I thought I'd share my experience in trying to get my K100rs started in the hope that it may help others down the track. I trawled through heaps off threads on this forum and others in trying to gather info and found that a lot of threads were never solved or maybe they were and some forgot to update their thread. 

When I purchased my bike I knew it would not start. It is a good clean bike. Only 44,000km. Hardly used. I thought it can't be too hard to get it going. It had been sitting for 8-10 years I estimated after looking at the date on the tyres and the state of the inside of the fuel tank. The bike looked great on the outside but inside of the tank was terrible! The fuel pump was gummed up with gunk and it didn't even have a vibration damper around it anymore. It had disintegrated into a gooey mess on the bottom of the tank. The strainer was also shot. 

I got stuck into cleaning the tank. Replaced fuel pump, vibration damper, strainer, all fuel and breather hoses. I had the injectors serviced and found 2 of the 4 were not that great and further testing found a third not playing the game all the time. It was on the way out. So I started researching injectors and reading lots of threads here again. I ended up running with injectors out of a Hyundai. 

So with a fresh Motobatt battery, spark plugs, fluids and filters it was all systems go. Time to crank her over for the first time.....

Well that didn't go to plan....

She seemed to start for a second or so and then cut out. I tried again. Didn't want to start at all this time....Hmmmm. I then noticed fuel dripping out the end of the header pipes. This isn't good. Out came the spark plugs to dry everything out. Next day I did the same and the bike behaved the same. There was way too much fuel being delivered.

I studied the forums some more and subsequently cleaned all electrical connections and ordered a new fuel pressure regulator as I didn't have the testing gear to test mine. Given there had been stale fuel in it for years I thought it was possible that the FPR had been damaged. It was the only part of the entire fuel line I overlooked when replacing it all. I whacked the new FPR on and got all excited ready to start her up. Hit the starter and the same symptoms as before were still present. She'd start for a second and then flood. Bugger....

Next came testing the coolant temperature sensor. Many threads spoke about this being a problem along with ground/earth issues and electrical connections. The coolant temperature sensor tested ok but I purchased another one just incase and it tested the same (I now have a spare). Rechecked and cleaned all connections and earth/ground wires. checked coils and leads and tested for spark. All good. I got all excited again and hit the starter. Still the same symptoms. Backfired and flooded. Damn you bike!!  

I pulled the injectors out but still attached to the fuel rail to see if the injectors were pulsing. I could almost guarantee that they weren't given the amount of fuel dripping from the header pipes after a couple short starts. Yep, the injectors open for the full 1.5 seconds or so while the pump was working after hitting the starter. There was no pulsing. Heaps of fuel! It was dumping in! Ok what next I thought....

Back to the study  ...

The ECU is getting a wrong signal from somewhere or the ECU is shot. The ECU was a quick and easy test so that was what I tried first before the next on the list, the Hall sensor and air flow meter. I called a mate of mine and asked to try his. Plugged it in and got everything ready for a start. Well I got the shock of my like when it started up with what felt like a half press of the start button. WOW!!!! I couldn't believe it. There wasn't even that much smoke. No where near what I was expecting. I'm up and running. Ended up being a very easy fix. 

Just goes to show that even though it may not be common for an ECU to fail....they do. A simple test may save a bit of time and money.... 

All the reading and study has equipped me well for any future problems I suppose....

Great stuff mate, can't wait to go for a ride! 

Good to hear it's up and running and thanks for posting the results. I am starting to notice a few ECUs going down the drain so it may be signaling that their life span is up and that going on yours and a few other posts it seems time related more than distance travelled.
I like it that you headed your post with the problem so that anybody looking doesnt need to trawl all the posts that say "Help this heap of S**t is driving me nuts". It makes it easy to find relevant posts.

RicK G wrote:Good to hear it's up and running and thanks for posting the results. I am starting to notice a few ECUs going down the drain so it may be signaling that their life span is up and that going on yours and a few other posts it seems time related more than distance travelled.

I haven't been into any of my ecu's, but I wonder if there may be some electrolytic capacitors in there that may be breaking down. 

I am an amateur musician, and some of the guitarists I know play through vintage amplifiers from the 50's and 60's.  One of the first things they do when the find an old amp is to replace the big capacitors that have gone bad over the years.

Could this be what we are seeing with these old Jetronic units?  Has anyone been into one of these units and taken any photos of the components?

I also recall reading that there is a transistor that switches the injectors that causes problems as well.  Supposedly, it handles a bit of power and is a weak point, but is fairly easy to replace.  With the heat these engines generate, it's easy to see how that transistor could be vulnerable.

Electrolytic Capacitors are renown for doing that. They dry out. Many computer motherboards now have the old fashioned paper capacitors, they haven't got as high a rating but go heaps longer. Some only last 4 to 5 years.

Rob Mack's next project?! 

Point-Seven-five wrote:

RicK G wrote:Good to hear it's up and running and thanks for posting the results. I am starting to notice a few ECUs going down the drain so it may be signaling that their life span is up and that going on yours and a few other posts it seems time related more than distance travelled.

I haven't been into any of my ecu's, but I wonder if there may be some electrolytic capacitors in there that may be breaking down. 

I am an amateur musician, and some of the guitarists I know play through vintage amplifiers from the 50's and 60's.  One of the first things they do when the find an old amp is to replace the big capacitors that have gone bad over the years.

Could this be what we are seeing with these old Jetronic units?  Has anyone been into one of these units and taken any photos of the components?

I also recall reading that there is a transistor that switches the injectors that causes problems as well.  Supposedly, it handles a bit of power and is a weak point, but is fairly easy to replace.  With the heat these engines generate, it's easy to see how that transistor could be vulnerable.

yes your right .75 ...but youll probably find that those big capacitors are big because of the voltage  not their capacitance rating ...some typical values used in those amps are 47 uf ..but at 450 volts ..a 47 uf capacitor at 25 volts measures just 6mm thick but at 450 volts could well be 30m thick and maybe a couple of inches long ..its all about the insulation properties

I'm my experience its the small value capacitors 47 uf and smaller .used for timing or coupling and some times rectification that die first in most modern electronics ...they just dry out because of cycles of charge discharge  and just plain heat  the dielectric just fizzles to a stop.

but a worthy reminder that many age related issues are not just all about rubber eh ?

I have the old ignition ecu from  kjustin and will be exploring the internals  to replace the switching transistor that operates the fi relay ...that died on his ..(I suspect that the current limit resistor on the collector
 is open circuit from a possible short circuit at some time in the fettling)  ...but
it will give me a better understanding of the components inside ...in many cases the electronics are not that sophisticated ...(but there is a chip with predefined operational functions inside )  but all depends on signal processing and electronics that feed it ...and signals that it controls

As is being said worth having a spare unit. What also happens is the part of the unit that retains the hook end of the plug from the loom cracks and you get a less than good connection. Last time I had running problems a swap of the unit cured it....I have this box with spare relays, all the units and ABS unit and if you have any space its worth grabbing and storing some of these. Most of the time you end up with a parts wait when in fact you can change things in the time it takes to make a coffee.

Now you have the K running its time to enjoy it and prepare for its stable mate I mean shed mate.

And then there's the rock and a hard place to add to this: new capacitors will last for years if not used but as soon as you start using them and if you then stop using them, they will fail. Many of our bikes have been stored for multiple years so yes, I agree that many of the ECUs are probably teetering on the edge.