Penta aq151 eratic at wot

[robjen1019]

Ok, aq151 with weber single carb upgrade. Petronics ignitor, new cap rotor and wires and plugs.

Ive got it timed right on 6 btdc as the manual says. Runs great up to about 5000 rpm. at that point the tach gets erratic and fluctuates between 5000 and 6000 rpms and the motor feels a little sluggish. If I back it off to below 5000 it straitens out. Tried messing with timing didn't seem to make a difference. Disconnected tach, I could still feel the sluggishness.

Any Ideas what is going on?

thanks.