I found one of your old posts about the idea of putting a manual clutch on a go kart. My brother and I are both engineers and we've developed a product to do so. We are very close to production, please check out our forum below for more information.
http://www.oldminibikes.com/forum/engines-modifications/69119-manual-clutch-horizontal-shaft-engine.html
Feel Free to post on the thread and we will be happy to respond.
Thanks,
Mike