I'm working through a similar issue with my VIP engine. I've tried shimming it a few different ways and have had it where the wheel will spin backwards without engaging the motor -but only with the crank nut relatively loose. I've read that the rubber clutches will swell in detergent oil, but I've also read that running the motor for a while will 'loosen' the tolerances between the first speed clutch and the starting plate / clutch drum.
Does anyone have any definitive experience with handling this issue? Thanks in advance!