Hi Albula,
Sadly all Whizzer models need upgrades, some more than others. The release date of the 2007 model will determine the upgrades needed. If it has the aluminum intake manifold it will most likely have the mushroom lifters [very important]. If it has the mushroom lifters they will need to be modified because they are way too heavy and the base needs to be reduced in length.
The late 2007 motor may need to have the aluminum cylinder re-cured to soften the threads [too brittle].
Milling the head, reshaping the combustion chamber, and modifying the restrictor plate will almost double the power, and make the motor start easier, idle smoother, improve gas mileage, and will accelerate quicker.
If the bike has an automatic clutch, it will need to be upgraded with a hardened bearing sleeve.
After the minor upgrades are implemented the motor becomes very durable and makes a very nice motorbike.
Have fun,