some hoses will separate from the gas exposure, you can check for this by removing that section of hose and then look to see if it's beginning to separate or collapse from inside. I've used a pre bent section of radiator hose before to make a charge pipe on an old turbo build I did and the hose didn't seem to mind the fuel exposure, but not all hoses are created equally.
Also check everything from the carb to the engine's intake port for any hardware that worked it's way loose, check that there are no cracks in the manifold or the carb base, check th throttle to make sure it's closing all the way etc... Since these are only one cylinder there's not much that can go wrong and not a lot to check so finding the leak should be fairly easy. Also pay particular attention to the rubber hose connection where the carb connects to the manifold for any cuts or damage caused by the clamps as sometimes the clamp can cut into the hose as it's tightened down.