1999 YZ 400F flogging?

I have a 99 YZ-400F.

The bike has ran perfectly fine in the past. Recently, I started to shift without pulling in the clutch ( trying new things)

Now, all of a sudden, at very low RPMs, If I pin the throttle, the bike just bogs until a few seconds then starts moving again.

Again this only happens when Im going slow and I being to open the throttle all the way

Is this a jetting problem ?

Thanks