Jerky movement low gear high revs?

[CBoz_imp]

When I stay in low gears (1/2) and take the revs up above 2000 and keep it there, the cb has a jerky motion, as if the fuel supply is not constant. The exhaust also sounds 'spluttery'.

Not noticeable in high gears and high speed (eg 100 km/hr in 5th).

Is this normal? EFI related?

6000 km service was 1000km ago, so the chain tension should be within tolerance.

Comments?

Thanks.