The reason they wont "cinch" up is the intake manifold is the same one used on the 50cc scooters that have a much smaller carb.
The manifold is called an "intake tube" and is listed as kymco part # 1711A. It is the tube that connects the carb to the engine (cylinder head).
Without exception EVERY Asian scooter that has this part will have a failure there. Depending on climate, and use they may last as long as 5-6 years without cracking but many fail in 2-3 years.
Everyone here look at yours for cracking. Pull the carb left/right, and up/down while connected, and see.
The crux of the problem is there is an aluminum inner core that has the molded rubber covering it. It is a BITCH to get that rubber off the core but with patience it can be done. I cut most of it off with a razor knife, and burn the rest off in a coffee can with a few ozs. of gas. Quick clean up w/ a wire brush, and you now have a proper part. All you need is a 2.5" rubber tube to re connect the carb to the engine.
The main symptoms are high idle after warm up, and a noticeable lag time on returning to idle when stopping. If you see red or Very light brown deposits on your spark plug that is also a sign of this issue.... vacuum leak. If left un checked this will lead to burnt valve seats, low compression, and poor throttle response.
check your manifolds guys... You all will be amazed at how many are bad. My guess is EVERY scoot that is more than 4 years old will have cracking
This is what I use to make the new "tube" (coupler)
http://www.wholesalemarine.com/mpi-reinforced-vinyl-tubing.html?gclid=CNb98M3-4r0CFSwV7AodsH0Ahg