Standard 50cc Dragsters are capable of around 35mph on average, after de-restricting expect to get something like a 10-15mph increase making this is one of the cheapest and most effective engine modifications for a 50cc Dragster.
 
Partial de-restriction. If you purchased your Dragster in the UK or any other country apart from Italy or Spain ignore this stage as this de-restriction will most certainly have already been done for you. UK Dealers normally do this de-restriction when they undertake what is known as a PDI (Pre-Delivery Inspection) before handing the bike over to the owner. Basically a washer or restrictor cone is removed from inside the exhaust down-pipe. With a restrictor cone fitted a 50cc Dragster is capable of a mere 24mph, Italian and Spanish laws dictate that this kind of restriction is necessary for teenagers to be able to ride as young as 14 years of age. Basically, the shape of the cone reduces the exhaust 'inlet' to around 1cm which restricts waist gases from escaping, with the cone removed an increase in gas flow is enabled allowing the engine to breath more easily. To remove the cone you would have to cut through the welding which holds it in place using a Dremel tool for instance.
 

 
1: Remove exhaust restrictor. This involves the removal of a closed-off restrictor pipe (or resonator tube) which protrudes from the side of the down-pipe (as seen in pic 2 and 3).
 

 
After un-bolting the down-pipe (pic 3), the next stage is to either cut the restrictor off (pic 4) and re-weld the hole, or squash the pipe together in a vice as close to the downpipe as possible. Removing the restrictor pipe altogether and re-welding is the recommended option as squashing the pipe will fatigue the metal making it more prone to cracking which will allow gases to leak and in the end won't do your engine any good.
 

 
5: With the exhaust restrictor now removed the hole on the down-pipe now needs to be re-welded.
 
6: Remove pulley spacer. The next stage of de-restriction involves the removal of what is known as a 'pulley spacer' or 'variator bush' as it is sometimes called (the terminology often varies). To locate this restrictor you will need to remove the transmission casing by unscrewing all the bolts.
 

 
Inside the case (pic 7), look between the two halves of the front pulley (variator) to see if there is a spacer. If there is, this is what you need to remove. What this spacer has been doing is limiting the gearing to a low speed ratio which prevents the bike from reaching 'top gear'.
 

 
Undo the center nut from the variator (pic 8), here we used a 17mm air gun, although you could also use a socket tool. Pay attention to the order in which the parts are removed so that you can put them back in reverse order.
 
Now remove the spacer (pic 9), it's a coincidence that the spacer also happens to resemble a wedding ring. Technically what's happening is the front and rear pulleys both slide in and out varying the position at which the variator belt runs between them. The spacer physically prevented the pulleys from coming fully together therefore limiting the highest available gearing.
 
With the pulley spacer now removed, re-assemble the variator in reverse order (pic 10). Re-fit the transmission case, bolt the exhaust back on securely and check all fasteners, go for a test ride.