Reduced top speed in each gear

Skepkymann · 2025-10-11T17:34:07-0400

Hello everyone,

I’m having a strange issue with my bike and wanted to see if anyone has experienced something similar.

The bike:

Sym NHT 200cc (EFI single, stock) 2023
Fuel pump: new (3 months old)
CKP sensor: replaced recently (1week ago)
Stator: replaced recently( with ckp)
Battery/charging: 14.1V when running, 12.5V engine off.
- Whole Clutch replaced recently as well.

The problem:

The rev limiter behavior has changed: it used to sound like the typical “bwaaah bwaaah” fuel cut, but now it’s a rapid bursts of “atatatatata” ignition cut style similar to a machine gun.
Top speed in all gears is reduced compared to before.
Example: in 3rd gear I used to reach ~94 km/h at redline, now only ~75 km/h before limiter.
In 6th gear, however, the bike still reaches its normal top speedeasily but get limited in rpm
When i hit 75kmh in third gear i can hear the engine screaming and if i continue holding WOT the bike kind of still accelerate a bit while rev limiter is engaging. And this happens in all gears
The rpm doesn't show in dash because of a burnt diode( it's an unrelated issue with the instrument panel)

Other notes:

-Bike runs normally at low and mid RPM.
-No issues during regular commuting—only near redline.
Sometimes when bike is cold i can get the top speed in each gear to rise a bit
-Changed clutch kit, with an OEM.

Has anyone come across this kind of behavior?
Thanks.

DannoXYZ · 2025-10-11T19:19:14-0400

Did you replace CKP sensor with factory OEM stock unit from authorised dealer?
Does it still misbehave if you put original CKP sensor back in?
This is standard troubleshooting procedure.
Undo last operation and see if that was cause of change.

Is there an adjustment spec in manual for clearance gap between sensor and trigger?
I remember using matchbook for this in old days.

Skepkymann · 2025-10-12T08:15:57-0400

DannoXYZ said:
Did you replace CKP sensor with factory OEM stock unit from authorised dealer?
Does it still misbehave if you put original CKP sensor back in?
This is standard troubleshooting procedure.
Undo last operation and see if that was cause of change.

Is there an adjustment spec in manual for clearance gap between sensor and trigger?
I remember using matchbook for this in old days.

Yes i replaced it with the oem part, and it was replaced at the official dealership

DannoXYZ · 2025-10-12T13:54:07-0400

Did it do this lower redline cut-out before or after CKP swap?
Should always ask for any used parts back with bike after repair, especially electronics.

Skepkymann · 2025-10-12T20:40:42-0400

All of the changes were made hoping it will solve the misbehave, except for the fuel pump, that was unrelated

DannoXYZ · 2025-10-12T22:18:06-0400

Well, now it's looking like output related rather than input.
Test ignition system components according to manual:

ignition coil impedances
wiring and connectors of ignition system
plug wire resistance
inspected spark plugs for being countrefeit

Emily Smith · 2025-10-14T15:12:40-0400

Yeah, that does sound odd, especially since you’ve already replaced a lot of parts. From what you described, it really seems linked to the new CKP sensor or how it’s reading the crank signal.

I’d start by checking the gap between the CKP sensor and trigger wheel. If it’s off even a little, it can mess with timing and make the limiter act weird like that “machine-gun” sound. Also make sure the CKP plug and wires are clean and seated tight.
If you still have your old sensor, try swapping it back in just to test, if the limiter goes back to normal, that confirms it’s the new sensor or its setup.
Would also be good to check the ECU ground and charging voltage at high revs, just in case. Keep us updated, curious to see what fixes it.

Reduced top speed in each gear

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