Hi there. I see your post and might be able to answer your questions. The hot air system is designed to give quicker warm up and more consistent running due to constantly hot air being fed to the carb from the ducting for the fan forced air cooling this motor uses. If cold air is ducted in the motor it will run differently according to ambient temperature (i.e. cold day will be lean, hot day will be rich). To avoid seizure the factory would be obliged to jet safely rich for cold days which means on hot days it would be down on power. Also the correct air temp will be fed to the carb quickly as the motor heats up quicker than the inlet tract. One more advantage would be better fuel economy with the leaner jetting permitted. The disadvantage is less outright power which is why you will not see it on racing machines.
I am ambivalent about pod filters. All of my GP race 2 strokes have fully sealed air boxes fitted, one as an expensive aftermarket addition. While they have elaborate means to overcome the pressurisation of the float bowls stopping fuel entering, our TGB scooters probably don't go fast enough to have this problem anyway. The TGB system seems to offer some "Ram air" which is a good thing.
Air boxes act as a surge tank which helps mid range considerably with no expense at the top end IF you make sure the box has no restrictions. This recovers the fuel mist that spits out the carb, especially at wide open throttle. Apparently 1 litre capacity is sufficient for 15bhp. I would "die" for 15 hp and pretty sure the air box is at least that big! What I did was to cut out the ribs from inside the air box cover. There is one long rib running the full length of the air box on the half that the "hot air hose" connects to. I left the little ribs in place that help support the foam. I used a "renovator" type tool to cut them out though if you had the time side cutters and blade knife would do it. I tried disconnecting the hose and it ran fine but I have rejetted accordingly as I also installed a pipe. Once I have installed a 70cc kit (where I have to remove the engine so can get easier access) I intend to cut off the pipe from the cylinder head end, block off the hole in the ducting with a piece of aluminium and have the hose tied into the fairing close to the hole the side stand pokes through to get cold STILL air. This is similar to what the GP bikes from the early 90's used before pressurising their air boxes. It then still looks standard!
Don't forget to remove the "donut" restrictor at the entrance to the air box!
