Hey, I know this must be a common one, but I've searched all over and can't find the answer! I have just picked up a 51 plate Speedfight cheap. Open the throttle and it decides for a while what it should do, then revs up, but it's lacking in power. I presume it's over fueling? Checked the plug also - picture below. Main jet was a 60. It's a Gurtner 12, with a manual choke? It's running a Leo Vince TT pipe. Thanks!