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.

Thanks Duck & JBT for your reply.
 
Yes, it was on my to-do list to do a Motronic swap.
Managed to do that today but unfortunately it’s no different.
 
Also just to clarify the flat spot, in 4^th or 5^th gear lower revs (sub 2k rpm) it basically just doesn’t want to pull, there’s always a prolonged hesitation until you eventually reach 3.5-4k rpm.
This is very noticeable compared to my other K1 which in 5^th will pull from any rpm/speed.
It’s like a misfire or fuel starvation but I can’t see how it be either of these with the work I’ve done.
 
Any more thoughts?
 
K-put

Why are you running a K bike in gear under 2000 RPM?  It's not a Camry.

You really shouldn't have it in gear below 2500ish.

The power curves that BMW published don't even start until 2000 RPM.

K1 power curves:

K-put wrote:All air & vac hoses/pipes checked from cracks (as best I can)

Did you use propane, Mapp or carb cleaner to check for leaks while the engine was running?

Laitch wrote:

K-put wrote:All air & vac hoses/pipes checked from cracks (as best I can)

Did you use propane, Mapp or carb cleaner to check for leaks while the engine was running?

 The inlet manifold stubs are notorious for hairline cracks that cause vacuum leaks. Especially in a 30+ year old motorcycle.
You spray around the manifolds and see if the idle increases. That's why Laitch suggested spraying around the manifolds.

Thank you again for the reply.
I’ve tried crab cleaner today and there was no noticeable difference in rpm fluctuations.
 
K-put

But did it improve the cleanliness of the crabs?
Regards a puzzled Martin.

Soonds a wee bit crabbit tae me.

(Yes, I did have a Scots girlfriend at one point...)

Doh!!
Aye sorry, I did of course mean carb cleaner.
Although cleaning crabs might be more successful.....


I did go back later and try some propane but again no difference.

All a bit of a bummer really!!

K-put

If you remove the oil filler cap at idle, does your bike stall?

No, removing the oil cap at idle don't do anything.

Just as a matter of interest, what was the purpose of that test?

K-put

Not sure if this is relevant, not sure about K1 bricks. Does yours have a Z hose between the crankcase and the plenum chamber?

My K100 does, therefore if l remove the oil filler cap, a large amount of unmetered air will get sucked into the plenum chamber and my brick will stall. I feel that you might have an air leak somewhere. Try spraying starter fluid around the Z hose, if you have one.

Here's another test I sometimes used to do to check for a lean mix. Remove the snorkel from the air filter box. Cover the opening by fifty percent, the revs will probably remain the same. Cover it by seventy percent, if unchanged cover it by eighty percent, if unchanged cover it by ninety percent. At some point the revs will change, if the revs increase, the air fuel ratio is lean. This might even work at the start of the snorkel, so then no need to remove it.

K1 dont have afm 

More likely needs a touch of advance on the hall sensors plate 

Did a k75 with similar flat spot last week

Good luck

charlie99 wrote:K1 dont have afm 

More likely needs a touch of advance on the hall sensors plate 

Did a k75 with similar flat spot last week

Wisdom and experimentation in this forum says not more than 6 degrees. If you face the HES plate that equates to rotating it clockwise 4mm from the normal timing position, where 4mm is a straight line from the edge of the notch in the normal timing position to the edge of the notch when the timing is advanced. Damn but I hope that made sense!

It works, BTW. It's not internet snake oil for once.

OK, just to be clear.
After I remove the T plate, I can slacken the two screws on the sensor plate and rotate no more than 4mm clockwise – correct?
 
I do have a different sensor plate from a spare engine so I could replace the unit completely (of course I’ve no idea of the history of the spare).
Is that just a case of remove/replace using the cut-out as the guide or is it more involved than that?
 
K-put

K-put wrote:After I remove the T plate, I can slacken the two screws on the sensor plate and rotate no more than 4mm clockwise – correct?
(...)
just a case of (...) using the cut-out as the guide

That's it, spot on. Put a pic up when you've done for us to confirm it's correct.

2mm is enough for that one 
From my experience

Heed Charlie. He's done far more versions of the K than I have.

It appears you have gone through the basics. I encourage you to check both ends of your HT wires. I had a similar issue and found one HT cable at the coil end was not fully plugged in. The bike would idle fine and at higher RPMs the symptoms were masked, but mid-range - especially with the engine pulling - it was very noticeable. Little things are easy to overlook but they are usually easy to resolve.

Well sorry to disappoint but once again absolutely no improvement after rotating the HES plate about 2mm.
 
I did quickly check the HT leads but as these are from a different bike and using a different set of coils I can’t see how it can be them.
 
Something else to add, if I slowly open the throttle and let the rpm pick up and keep doing this as the bike increases rpm and speed its actually OK.
However, if I open the throttle move than the rpm has picked up the lag / flat spot is painful.
 
Going to take my other K1 to work tomorrow (150 mile round trip!) so I’ll remind myself how much better it is compared to the sick one!
 
 
K-put

K-put wrote:Something else to add, if I slowly open the throttle and let the rpm pick up and keep doing this as the bike increases rpm and speed its actually OK.
However, if I open the throttle move than the rpm has picked up the lag / flat spot is painful.

Maybe you've got a worn cable connection at the throttle grip, or the cable is compromised somewhere along its length.