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Occasionally losing power!

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Farshad

Farshad

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Joined
Mar 16, 2026
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12
Location
United Kingdom
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Bike
R18 Roctane
Hi all, I have noted occasional power loss not on motorway speed, but instead on city ride on a hot day with a lot of stops and starts on the first and second gear. I think the engine became hot and then on the take off from stop, the throttle revs but it does not transmit immediately to wheel. it became very sluggish to take off and more throttle, rev goes up, no response, and all of a sudden a spin and a bit of losing balance because of sudden rear spin! I mentioned it to the dealers on its running in service and they said they couldn't see anything wrong, but report if it happens again, then again it happened on another hot city ride day! Strange thing is, on a normal ride, it is ok and no problem!
Anyone else has had similar issue? mine is 2026 Roctane
 
Sounds weird. It’s not easy to see the instrument cluster warning lights sometimes (in bright sunlight), have you been triggering the traction control by giving it a handful of revs away from the lights perhaps?
 
Interesting thing is that the warning sign does not give any clue! and no, never touched the traction control button to be honest, never take this bike off road, not that it is designed for one anyway. I think instead of dedicated traction control button they could have added loads more basic functionality, like fuel and temperature gauge or engine temp, but that is a different topic
 
Perhaps your clutch lever needs to be adjusted, or perhaps your hanging a finger or two on the clutch lever and not letting the clutch to fully engage and transfer the energy to the rear wheel?

Did you do any work that required new or longer hydraulic lines? Maybe air in the clutch line?

You can open up the reservoir and finger the lever rapidly and see if you get any air bubbles; position the bike, so that the clutch line is as vertical as possible, it order to allow any air to travel straight up and out. Try to remove any bends and such...

Just a thought.. I haven't experienced anything along those lines though..
 
Star-Lord said:
Perhaps your clutch lever needs to be adjusted, or perhaps your hanging a finger or two on the clutch lever and not letting the clutch to fully engage and transfer the energy to the rear wheel?

Did you do any work that required new or longer hydraulic lines? Maybe air in the clutch line?

You can open up the reservoir and finger the lever rapidly and see if you get any air bubbles; position the bike, so that the clutch line is as vertical as possible, it order to allow any air to travel straight up and out. Try to remove any bends and such...

Just a thought.. I haven't experienced anything along those lines though..
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Thank you Star-Lord, I thought of the clutch lever and have adjusted it, but that was not it. No work to the hydraulic lines, the bike has only 700 miles on, the air bubbles I will check.
But as I mentioned it only happens when I have been riding in over an hour in hot day. The only mod I have done, since day one, was to drill out the muffler end, after reading on one of the forum threads that it was safe to do. To be honest, I had no issues with that, the sound got throatier and i have had almost 600 trouble free miles till this problem has showed up. Not sure if the engine needs tuning to the new air flow after the mod?
 
It doesn't sound like you mentioned a difference in the engine's performance; however, after re-reading your post, I did note that you mentioned starting in 1st and 2nd gear...

1st gear is definitely the way to go, when starting from a dead stop.. 2nd gear would be struggle for a Model B/TC; I'd avoid starting off in 2nd gear...

The mention that possibly the issue is temperature related; perhaps, expansion of the clutch fluid due to a temperature coefficient is related to the issue? Sorry for being so clutch related focused...
 
Star-Lord said:
It doesn't sound like you mentioned a difference in the engine's performance; however, after re-reading your post, I did note that you mentioned starting in 1st and 2nd gear...

1st gear is definitely the way to go, when starting from a dead stop.. 2nd gear would be struggle for a Model B/TC; I'd avoid starting off in 2nd gear...

The mention that possibly the issue is temperature related; perhaps, expansion of the clutch fluid due to a temperature coefficient is related to the issue? Sorry for being so clutch related focused...
Click to expand...
Sorry, I probably did not explain it well. I meant it gets sluggish on the first and also on the second gear,- not starting on the second gear. So, when it happens, say I stop at the traffic light, then about to go, engage first gear, then more gas than usual for the take off...and it moves slowly as if the clutch was still engaged, I rev more, but no speed transmission to wheel. then i go on the second gear at lower rev and still the same delay in power transmission when i speed up. I think you might be correct about the clutch. I will have a look later this evening on my ride back home, as it happens it will be about 17 degrees here in London! so relatively warm day. the problem might present itself again
 
emgarciax said:
Could it be a limp mode to avoid overheating?
Click to expand...
Interesting point. Didn't know it had one. You mean to protect the engine in case of catastrophic F failure of sort. Not sure. Because you would expect the dash or warning lights go Christmasy if that happens. There was no fault in the warning panel then. But the feel of it was exactly that. Massive loss of power at reduced or limited rev. I guess i have to take it back to dealership and leave it there for them to do some long running test.
 
As a bit of an outlier, one possible cause is that the clutch master cylinder has an adjustable "piston" that closes when the clutch is pressed so that tne clutch line is presurised..... and when the lever is released it opens so that the clutch reservoir and line are connected and fluid can "equalise". If the piston doesn't travel far enough to open the "port" on release, the clutch line is effectively sealed and the trapped fluid expands with heat and applies some pressure so the clutch can slip..... keep in mind the r18 has a slipper clutch as well so it can be a bit weird.

This has been discussed somewhere here before. I''ve adjusted mine (brake is the same) to fine tune "take up point" but that is another matter.

Generally, a check to see if the piston is set ok is to remove the reservoir lid, press the clutch a few times and see of there is a ripple in the clutch fluid indicating fluid is traveling betwee the line and res.

As far as how this could be so? 1. Not set correctly when manufactured (you bike is newish) 2. The relevant "lock scew" has relased a bit allowing the piston to migrate (lock screw does normally have threadlocker on it). 3. New levers added and piston position not set correctly.

Old man recall suggests someone had this issue 2-3 years ago.

Here ya go..... https://www.r18forums.com/threads/clutch-issue-for-r18-transcontinental.523/#post-56160

Manhatten matt posted this in there......

"Noelpolar's advice is true and very accurate. The clutch on my 2023 R18 Pure with under 5,000 miles began slipping on a recent 4-week trip to the eastern Canadian provinces. It was diagnosed in New Brunswick to be a slave cylinder issue, but they would not make repairs because USA and Canada warranties are not reciprocated. I "limped" the bike back into Maine, then rented a U-Haul to take the bike to Pennsylvania where I had trailered my bike to meet up with my riding buddy. Once back home in Texas, I took the bike to BMW San Antonio, and the tech there correctly diagnosed the slipping clutch problem to be caused by a misadjusted clutch lever friction point. Such a simple solution for a major problem. Bike is still in the shop awaiting new clutch lever parts under warranty, but I'm assured the problem is fixed. To the OP, please read this post and share with your dealer/service manager."

I only reposted this because no one has ever said I give "true and accurate" anything..... and it wasn't that long ago, though since we adjusted our clocks for daylight savings a few weeks ago time has definately slowed down.... so that explains the 2-3 years.
 
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Another possibility is that one of the wheel sensors is bad - this would cause the anti-lock/ traction control to reduce power. It would be odd however that this does not happen on the highway. I have seen wheel sensors get fouled up with dust/ dirt especially with soil having high iron content. This was off-road however.
 
Thought I'd chime in after Noelpolar reposted my comment about "loss of power" due to a slipping clutch. On a long 6,000 mile trip to the eastern Canadian provinces last summer, my bike started to "lose power" in all gears and in all modes on acceleration. The bike would rev, but was sluggish to engage. Techs in Canada thought the problem was the master cylinder, but the eventual diagnosis and simple fix was that the clutch lever friction point was not adjusted correctly. Don't know if this is the solution for Farshad, but happy to complement Noelpolar on his memory retention. Ha! :)
 
Star-Lord said:
ever, after re-reading your post, I did note t
Click to expand...
Manhattan Matte said:
Thought I'd chime in after Noelpolar reposted my comment about "loss of power" due to a slipping clutch. On a long 6,000 mile trip to the eastern Canadian provinces last summer, my bike started to "lose power" in all gears and in all modes on acceleration. The bike would rev, but was sluggish to engage. Techs in Canada thought the problem was the master cylinder, but the eventual diagnosis and simple fix was that the clutch lever friction point was not adjusted correctly. Don't know if this is the solution for Farshad, but happy to complement Noelpolar on his memory retention. Ha! :)
Click to expand...
Thank you for your input, I will sure to pass that on to the dealership in case they can't diagnose it correctly.
 
Noelpolar said:
As a bit of an outlier, one possible cause is that the clutch master cylinder has an adjustable "piston" that closes when the clutch is pressed so that tne clutch line is presurised..... and when the lever is released it opens so that the clutch reservoir and line are connected and fluid can "equalise". If the piston doesn't travel far enough to open the "port" on release, the clutch line is effectively sealed and the trapped fluid expands with heat and applies some pressure so the clutch can slip..... keep in mind the r18 has a slipper clutch as well so it can be a bit weird.

This has been discussed somewhere here before. I''ve adjusted mine (brake is the same) to fine tune "take up point" but that is another matter.

Generally, a check to see if the piston is set ok is to remove the reservoir lid, press the clutch a few times and see of there is a ripple in the clutch fluid indicating fluid is traveling betwee the line and res.

As far as how this could be so? 1. Not set correctly when manufactured (you bike is newish) 2. The relevant "lock scew" has relased a bit allowing the piston to migrate (lock screw does normally have threadlocker on it). 3. New levers added and piston position not set correctly.

Old man recall suggests someone had this issue 2-3 years ago.

Here ya go..... https://www.r18forums.com/threads/clutch-issue-for-r18-transcontinental.523/#post-56160

Manhatten matt posted this in there......

"Noelpolar's advice is true and very accurate. The clutch on my 2023 R18 Pure with under 5,000 miles began slipping on a recent 4-week trip to the eastern Canadian provinces. It was diagnosed in New Brunswick to be a slave cylinder issue, but they would not make repairs because USA and Canada warranties are not reciprocated. I "limped" the bike back into Maine, then rented a U-Haul to take the bike to Pennsylvania where I had trailered my bike to meet up with my riding buddy. Once back home in Texas, I took the bike to BMW San Antonio, and the tech there correctly diagnosed the slipping clutch problem to be caused by a misadjusted clutch lever friction point. Such a simple solution for a major problem. Bike is still in the shop awaiting new clutch lever parts under warranty, but I'm assured the problem is fixed. To the OP, please read this post and share with your dealer/service manager."

I only reposted this because no one has ever said I give "true and accurate" anything..... and it wasn't that long ago, though since we adjusted our clocks for daylight savings a few weeks ago time has definately slowed down.... so that explains the 2-3 years.
Click to expand...
Thanks for that Noelpolar, I have booked it with the dealership for a check up, I will pass this to them too.
 
I didn't read everything posted above but after reading most your original post this is the exact same scenario that my friend and I have when we were stuck in traffic on i-95 in Florida in the 88° temperatures with the bikes overheating. I tune my s1000rr 2024 model and I can tell you there is a timing table that is designed to protect the internal engine components when heat becomes a factor. There is about 10 different timing tables off the top of my head. So yes it sounds like a factory designed limp mode.

P.S. theoretically one way to help with this would be remove the valve in the exhaust. So at low RPM the valve isn't restricting the exhaust from exiting the bike for the stupid sound emissions. There is a video that goes into detail about the operating parameters of the BWM exhaust valve.
 
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And when you take the bike in for a check-up, make sure the tech gives it a thorough test ride long enough to get the bike up to running temperature before making a diagnosis. When I was having the slipping clutch problem on my R18, it only manifested itself once the bike had warmed up. Keep us posted on what you find out.
 
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