K100 cut off at 5000rpm

[VanBulck]

Hi Guys!

Long time reader, first time writer 

I have a problem that I can't seem to find an anwser to. My K100 cuts off when I rev above 5000 rpm. In top gear this is at about 125 kph. It would just kind of hesitate at firs, and then completely cut off for about 3-4 seconds (no power at all), after which when I close the throttle and wait for a few seconds, everything seems fine again...
There is only a problem above 5000 rpm, under 5000 rpm everything seems fine and the bike pulls good, no problem at al. It's only when I rev above 5000 rpm that the engine starts to hesitate and eventualy cut out.

This problem just started about 200k ago. Before I had no problem at all.

I recently (600k ago) did a clutch spline lube and replaced the water/oil pump.

Does anybody have an idea what the problem could be? Something with the ignition maybe? I don't think there is something wrong with the fuelsystem, since I have full power untill I reach 5000rpm...

Thanks!

Greatings from Belgium,
Pieter

[Howard64180]

I know the rpm is different, but I wonder if it has anything to do with this 'Hint and Tip' from Motobins' website:
'A K-Series Which Will Not Exceed 50 mph or so is not fun, and the answer could be that the throttle switch is jammed, so telling the injection unit that the throttle is closed; in this case, it will shut off the fuel supply above engine speeds of about 3,000 rpm.'
Hopefully someone with more knowledge will be along soon.

[VanBulck]

I just adjusted the throttle switch, and I can hear it clicking when I open/close the throttle, so I don't think there is anything wrong with it, at least not mechanicly...

Things went from bad to worse yesterday when I rode home from work. I was driving on the highway at about 110 kph, when suddenly the power was gone completely! I could only rev until 2500 rpm. So top speed in 5th gear was 60 kph  :yow I was lucky I was near an exist, so I left the highway and limped home at 50-60 kph. Even when I rev in neutral, I could only rev until 3500 rpm. So my bike is not driveable until this issue is fixed.

I'm going to pull the spark plugs today to see what they can tell me...

[rbm]

Clogged fuel filter?  Possible bad fuel regulator?

[VanBulck]

Just changed the fuel filter 600km ago.

I don't think it's a problem with the fuel system since I had no problem at fuel throttle until I reached 5000rpm. Torque was good until the 5000rpm mark was reached...

[rbm]

Then possibly the ignition control unit under the tank is acting up.  But first check the HES for proper operation.

[Scott_]

Robert, did all K100 have the ignition amplifier module or only the later 16V versions.
I haven't seen where the OP has said what year he has.

[rbm]

Scott, His profile says only k100 with no year so I can't say whether it's 8V or 16V.  I was referring to the ICU near the headstock, which all K75/K100s had.  I was not intending to refer to the ignition amplifier for use on the K1100's with Motronic.

[Scott_]

Scott, His profile says only k100 with no year so I can't say whether it's 8V or 16V.  I was referring to the ICU near the headstock, which all K75/K100s had.  I was not intending to refer to the ignition amplifier for use on the K1100's with Motronic.

Yea, I know you were referring to the main ICU. I was just asking for my knowledge if all 100's had the amp.
I know the '93 1100's had it as well as the 16v 100's, but didn't know if any of the 8v 100's had it or not.
I have heard of heat related issues with these amp units when the heat sink paste dries out.

[VanBulck]

It's an '85 K100 8v...

Started pulling things appart this weekend, going to test the HES one of the following days!

Found another issue, but I don't know if this is the culprit or not. When I removed the TB's and airbox, I noticed there was a lot of oil inside the airbox and on the TB's!  :dunno There is actually a little pudle of oil inside the airbox! How is this possible? I noticed my crankcase breather hose was cracked, but I didn't think this could cause such a problem... Is the cracked hose the culprit here or is there something else wrong with my engine? I'll post some pics of it later today...

[VanBulck]