i have the same problem but solved it.. firstly unscrew the engine from the chassis and put your engine a side for a moment. Align the starter box wheel with the flywheel slot on the chassis. After you adjusted the chassis mount screw or whatever you call them, put the chassis on the starter box, with the starter box switched off and press down on the chassis as if you are going to start your engine and try turn the starter box rubber wheel with your finger if you can't turn the rubber wheel keep trying but lift the chassis up, this should result in the starter box wheel being free. this means you have to get a file and file down the chassis to the desire size that your starter box wheel can spin freely while the chassis is being firmly pressed down on the starter box wheel. then put your engine back in and enjoy