Hello from Perthshire Scotland to fellow K owners.

I’m a relatively new member and I’ve sent a bit of time reading up on previous posts regarding an issue I have with my 1990 K1. I’m actually the proud owner of two of these bikes, both in blue and both UK original specs. One bike has done just under 10k miles and the other 24k miles.
 
Strangely it’s the less mileage 10k bike which causing me problems.
 
Basically it runs rough and a bit lumpy but the main thing is a massive flat spot.
 
On the road, from tick over to 3-3.5k rpm the pick-up is painfully slow and rough. Above 3.5k rpm it seems fine (or better).
 
So, from trying the basics and reading stuff from the forum, this is what I’ve done so far –
New plugs
HT leads changed from another bike
Coil packs changed from another bike
Fuel tank cleaned, new fuel filter and internal hoses (there was a split hose).
Good steady flow of fuel returning to tank thru’ the rev range
All air & vac hoses/pipes checked from cracks (as best I can)
Injectors removed, cleaned, checked and new seal kits
Carbtune showed everything was in reasonable balance
Output side of fuel pressure regulator checked.
Throttle body switch checked (using 3pin GS-911 tool)
Ignition Amp module removed, cleaned and new thermal paste added
 
All of this has got me absolutely nowhere, not a single bit better or improvement!
 
Any ideas?
 
 
PS – due to work commitments it might take me a while to try any suggestions.

Next thing I'd try is swapping Motronics with your other K1.

K1 has a flat spot near 3500/4000 rpm. It's the design of the engine features that create it, to benefit more "brutal" power in high RPM.
It's very sensitive on my K1 with sidecar.
I'll get rid of the K1 camshafts one of these days to replace them by K1100 camshafts, with more torque at lower RPM and no flat spot.