Hi folks,I've hit a bizarre problem on my 84 k100.

She runs real nice,until you hit about 5200rpm then it's just like it's hit a rev limiter.If you try to hold the throttle at this point the rev fall away then pick up til they hit 5200 again.Very much like a spark cut rev limiter,but not quite as sharp.

Have replaced ecu and ignition unit,with no change.I'm thinking coils but haven't got spares with me.

Any ideas,anyone had a similar problem?

Thanks for looking.

battyone wrote: Have replaced ecu and ignition unit,with no change

Sorry, I am confused...

The 1985 K100(2v) has 2 separate units: The Fuel Injection Unit (L-Jetronic) and the Ignition Control Unit.
When you say "Have replaced ecu and ignition unit", are you talking about these 2 Unit?
Generally ECU (engine control unit) is referred to a single unit controlling both Fuel Injection and Ignition Timing.

The K100 has a rev limiter but it's supposed to disable the signal at pin #8 of the Ignition Control Unit only when the engine reaches 8905rpm.
If pin #1 of the LE-Jetronic doesn't receive this signal , the fuel injection is disabled.
When the engine speed is down to 8900rpm, this signal is re-enabled.

If the problem is persistent and occurs even if the engine is not under load you could use these 2 methods to identify the source of your problem.
With the bike on the center stand:
Connect the inductive lead of a strobe light over the spark plug wires to visually monitor the ignition.
Install an LED on one injector to visually monitor the signal from the LE-Jetronic.
Try to rev your engine over 5,200rpm and see what fails.

Let us know what you find.

sorry for confusing you.Yes I have replaced the injection control unit and the ignition control unit.

Will try the strobe method shortly,I have one of those with me.

Have tried the strobe method,with no obvious break in spark.
Therefore must assume -for now- that fuel injection is being cut.
Have tested water temp sensor and appears fine reading 450 ohm with engine hot.
Will investigate further.

Almost solved,low fuel pressure!

So either pump or regulator.I suspect regulator as clamping return hose had the bike running better.

I have the spares just got to dig 'em out a try them.

Regards Nige

Hi Nige,
Sounds like you are on to it and homing in on the problem good thinking!
Regards,
K-BIKE

Thanks K,not sure it was good thinking just went thru everything until I ran out of things to replace.

What really confused the issue was the fact that I had wideband O2 fitted.When this "rev limit" was hit the display was resetting itself.This indicated that something electrical was going on...the sensor was powered by an ignition +12v.

Then I decided to change spark plugs again,found 1&2 black and sooty,3&4 spotless,just like new.this pointed to fuel probs.i swapped the O2 sensor to no4 pipe and lo and behold it was off the scale lean?????

I thought it might be a fault on the injector harness...no signal to 3&4 but that all checked out.so I stripped the fuel log off incase of blockage.Nothing there either.Put it all back together and was about to load her on the van,when a friend suggested clamping the return hose.Bike instantly sounded better then went thru the previous 5200 block.That really suggests the regulator,but why that would then give 2 rich plugs and 2 lean I'm not sure,I can sort of get my head around the 1st 2 injectors getting a bit more fuel but not the last 2 getting almost nothing in comparison.

Well a pressure test on the pump and the system will tell the story-I hope.

Thanks folks Nige.

Better have a look at your coils and the hall sensor as well.

Hi Rene,output from coils was tested on all plug leads with a strobe.No sign of any problem at the 5200 choke point.
Coils and leads were all checked for resistance and everything swapped around to check for any differences
Plus would expect coils or sensors to affect 1&4 or 2&3 not 3&4 as was found.

Now I'm home there's no panic and I have spares for everything.Soon I'll even have another one up and running so I can swap parts knowing they work.

Pump pressure relief valve failed.Pumped 150psi + and broke my pressure test gauge.From CF's excellent how to's i understand should be 65psi.

2other pumps tested one does the same,other doesn't spin.
I have one more to test,but it's in an old tank-with no key-so I don't expect much joy there.

Time for a new one...unless there's a repair for the pressure relief valve.
Or could I rig another regulator in line to limit the pump pressure???

Open one of your faulty pump. The pressure regulator may be stocked with "guck" and a good cleaning may solve your problem.
I am surprised that you didn't burn the fuse.

Bert

Thanks Bert,it did blow a fuse when I tested the pressure output.

I had wondered whether the valve was just stuck,the current unleaded fuels over here do seem to be particularly unpleasant,I had the float needles on my bonneville "glued" shut recently the tips had softened.

The one pump is completely dead,I was going to rip it apart to examine the internals.In the meantime I'm going to order a new pump.

I'm still a little suprised at my symptoms though,I had a similar problem with another bike, a couple of years ago, and it flooded the bike with fuel.

Have managed to salvage 2 pumps.

I had one pump that was obviously beyond help,so I used the excellent instructions posted here to dismantle it so that I could better understand the pressure relief valve.

Pretty simple really,just a sprung "ball",even in the damaged pump there was no accumulation of gunk to prevent it's working.So they must just "stick" to their seats and refuse to budge.

While exploring methods of freeing the valve on an intact pump-the "ball" has a very useful "stalk" which allows, with very fine needle nose pliers, you to pull it off it's seat-I realised that you can quite literally "screw" the spring out and remove the valve.This allows a good clean.It's a little fiddly "screwing" the spring back in but I now have 2 working pumps.

Pressure testing shows them to still be a little high,85 and 80 psi,but the pressure relief can be heard bleeding off.When connected to the complete system normality has returned with 36psi.

Alas the problem has not gone,I suspect that injectors 3&4 have failed,so back to the workshop later.

SORTED!!!!

Replaced 3&4 injectors and normal service was resumed.

Both of these injectors appear to work when tested,but in the end I resorted to reconnecting the fuel rail with the injectors out of the head,not the safest thing to do,but short of building an injector test rig???

1&2 good healthy spray,3 intermitent and 4 dribble.So problem solved

Whether this is connected to the overpressure from faulty pump or just one of those things???? guess I'll never know for sure,maybe the regulator was actually coping with the overpressure and the only fault was the injectors??

Now I can refit all the extras that I use for racing,as I disconnected everything when the original problem occurred.

Launch limitter,shift light,shift kill and all of the nitrous kit.I have 2 potential chances to run on the track left this year,fingers crossed for good weather.
It's time this thing ran in the 11's,she's been too close for too long.
Next year a purpose made track bike will be sorted,longer,lower, lighter and possibly I'll get the turbo sorted!

Great site gents some very useful info and especially the how to's.
Hope my trials can be of some use to someone.

all the best Nige

You cant leave without pix!

Don't panic I'm not going.

I'm on my notepad-no pics on here,as soon as I get chance to hook up my desk top I'll post some pics.

Can I post from facebook???quite a few on there.

I'll get something sorted...it's a long story but I moved house couple of months ago

A little appetizer,keep you going til I sort some more out

"Hope my trials can be of some use to someone."

Doesn't matter what you do to a K, if you post it on this site, it will help someone.

I'd be interested to see how the splines on the final drive stand-up to the drag strip environment.

Clutch is the first thing to cause trouble.Has to be in pristine condition or slips quite easily.Going to look into making my own replacement with sprung centre.
Rear suspension has to go otherwise the shaft jacks up the rear end and unloads the tyre.
This one wheelies off the line quite nicely now,launching at 6000rpm with a wide open throttle.

In the past the only real trouble I've suffered from is piston related.Kept breaking ring lands and 2nd ring.And have had a couple of small issues with the nicasil bores.

The piston prob was related to my method of nitrous and additional fuel injection,with the fuel being separate from the nitrous.I have now returned to "fogger" style injection.The bore trouble maybe down to age,we have to see if I have anymore probs.

As far as the shaft splines go,I'd have thought the rubber shock absorber would be more likely to give,but I've seen pictures of clutch splines in pieces so who knows.I plan to make an extended shaft using later paralever parts so I'd actually be adding another set of splines too.

The K is cheap fun,bits are easy to come by-I've just bought another motor for £30.A lot cheaper than my bonnie,where 2nd hand motors fetch £1500.
I really like trying to go quick on something that isn't supposed to.It's much more of an achievement,I even had panniers on for a while and hid the nitrous bottle inside.

Excellent stealth rocket ship to wipe the smile off the faces of those who might initially sneer at a BM. Really well done for flying the flag for us to show what can be done.
Regards,
K-BIKE