Flat spot in the rev range...

[RWH_900]

Hey All...

New on the forum, desparate for some mechanical advice.

I have a rather pronounced flat spot in the rev range. Most noticable in 2nd gear between ~2,000 & ~4,000 rpm.

Is this likely something I could diagnose and fix myself or should I seek professional help.

Cheers,

RoB.

[3alfa3]

same here (stock 2020 Z900 with 50.000kms - noticed that at 35.000-40.000 kms, very slightly, but now is very pronounced. 2nd gear most noticable, between 2000-3000rpm. Even 3rd and 4th (possibly 5th and 6th, but i never ride in that rpm range except 1st and 2nd gear in city trafic). Over 3000rpms no problem at all.
1st gear: smooth as silk, no matter what rpm, and that is what confuses me.
Also, problem is there no matter what ride mode i use: sport, road, rain.....

No backfiring from the exhaust, no smoke, unburned fuel smell, nothing, just flatspot between 2000-3000 rpm in 2nd and higher gears. In 2nd, 1900-2000rpm: smooth, just as above 3000rpm. But in between..... not good at all

Going to visit Kawasaki dealer/service in next 30 days (with very good reviews, knowledge, experience for many decades) for opinion and resolving this issue which was not there before, so it must be something wrong, but never had check engine light, error codes etc displayed.

[RWH_900]

Think I'll do the same... 🤞they don't just blow me off or try to rinse me. Good luck!

[zed9]

Quite possible needs a throttle body sync.

[3alfa3]

Originally Posted by zed9

Quite possible needs a throttle body sync.

Could be, and that would be simple and cheap to fix at a Service. But, my Z900 idles smooth and there is no (even a hint) flat spot when riding in 1st gear. Could throttle body out of sync manifest in that way?
My thoughts are also about throttle body, TPS or some other sensor working out of specs etc.

[zed9]

Originally Posted by 3alfa3

Could be, and that would be simple and cheap to fix at a Service. But, my Z900 idles smooth and there is no (even a hint) flat spot when riding in 1st gear. Could throttle body out of sync manifest in that way?
My thoughts are also about throttle body, TPS or some other sensor working out of specs etc.

True. You usually feel the out of sync either at idle or just off idle.
Maybe plugs or sensor because the Z is inherently smooth so something is off. Mine is doing it lately too.
I have a sync tool but no time.

[3alfa3]

In my case, that definitely started barely perceptible and is getting worse, progressing linear (first noticed about 10000-15000 kms ago).
What i noticed is that at the begining, problem was in narower rpm range (2600-2800), now is in between 2000-3000 and much more pronounced.

[Cazzy_R]

Originally Posted by 3alfa3

.......there is no (even a hint) flat spot when riding in 1st gear. Could throttle body out of sync manifest in that way?

 If the ETV mapping for 1st gear is different it might be masking the problem apparent in the other gears.

[zed9]

I just recently started noticing a slight hesitation rolling on the throttle from maintenance throttle that was never there before. It’s probably in second or third gear. I haven’t yet pinpointed it as it just started.
I noticed it rolling on throttle as I was negotiating a tight corner in a low gear at lower rpm. During straight line riding under normal acceleration while shifting up through the gears it’s not obvious.

[3alfa3]

UPDATE:

51.000km, official Kawasaki service with excellent reputation for several decades.....
New spark plugs, new air filter, throttle body taken out and cleaned thoroughly and synchronized after reassembly (it was dirty, seen it with my own eyes, deposits ("sludge") everywhere, idle speed was 500rpm higher after cleaning - i had to correct idle speed twice in last 51.000km - it got to low twice so i bumped it up to 1100).....

I replaced air filter at 28000 km, it was dirty, but not much. This Hiflo air filter after 23000 km was clean almost as new. It is dry from the factory, OEM filter is oiled (very lightly, but oiled) and filters more efficiently, that's why throttle body was dirty. Not worth the savings given OEM filter is good for roughly 25.000kms.

Did not solved the Problem entirely, it is less pronounced, but still there.


Still, one thing that confuses me: 1st gear is smooth as it should be, but 2nd is not good between 2000-3000 rpm (god for 1900-2000rpms then bad in between 2000-3000 and good above that), so is the 3rd, 4th but much less pronounced than second gear.