You could look into the whizzer complete engine kits available on eBay alot... Probably one of the more powerful complete kits...should just need a cruiser bike to slap it all on and be done.... 2 strokes...step aside please
If it means reliability and it will last for a long time, It's something I'm willing to work towards But if I later decide otherwise will definitely buy an R80cc engine kit from ebay and use some upgrades from sick bike parts.