$16 - A9 in SB vs Karate Kid

[mattiesmat]

BB was 57/14.
I felt my hand was too good to fold preflop.
On the flop I decided to cbet, but is that good against a karate kid?
Karate kid here means a donk that thinks you are stealing (and bluffing on flop) and will not give up. (quote sence)

PokerStars No-Limit Hold'em Tourney, Big Blind is t50 (7 handed) by Hand Converter CG

CO (t1085)
Button (t5155)
Hero (t2110)
BB (t1415)
UTG (t1300)
MP1 (t1680)
MP2 (t755)

Preflop: Hero is SB with A[img]/images/graemlins/diamond.gif[/img], 9[img]/images/graemlins/heart.gif[/img].
<font color="#666666">5 folds</font>, <font color="#CC3333">Hero raises to t150</font>, BB calls t100.

Flop: (t300) 5[img]/images/graemlins/spade.gif[/img], J[img]/images/graemlins/diamond.gif[/img], 2[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets t175</font>, <font color="#CC3333">BB raises to t350</font>, Hero folds.

Final Pot: t825