Hi Go,
In order to make the 2005 model reliable several changes need to be considered. It is VERY important to convert to mushroom style lifters right away. When I tested the original NE5 motor the lifters "ate" the camshaft lobes. The reason this happened is because of poor engineering, no quality control, and little [or no] tesing a new product prior to release for public use. When I contacted the main office in TX and explained the problem, I also told them of the fix. Because of the size and angle of the lifters, the 10 MM lifters are too small and "dance" down the camshaft lobes, cutting deep holes in the lobes. The cure was simple, just increase the size of the lifter that rides on the lobes [mushroom lifters], however that would cost additional money to change. Instead of fixing it correctly, they simple softened the lifters and hoped no one would catch the problem during the warranty period. In late 2007 they started fixing the problem by using the mushroom lifters, however they altered the original design I offered them in late 2004. I even supplied them with modified lifters to use as a pattern, but something got lost between the USA and Tiawan. I used a set of Whizzer "vintage" 1/2" lifters and cut the area that rides in the crankcase down to 10 MM [.393"] and left the bottom 1/8" the original size [1/2"]so that the lifter would stay on top of the lobe longer, and then "roll" over easily onto the ramp. The original 10 MM and the vintage lifters were center drilled [approx. 80% of the length], however the current product mushroom lifters aren't and are way too heavy, the base is way too long and often cut at an angle [causing the clearance to change as the lifter rotates]. Because the current lifters require so much additional machine work to make them correct, I commisioned an American company to make them correctly, but the demand is great, and most are already sold [less than 25 sets will be left in stock].
Another area that needs attention is the head gasket, the original steel unit often blows, and should be replaced with a copper version [the current offering from Whizzer will not work on the earlier cylinders unless modified]. I suggest contacting the nearest dealer and try find the earlier version copper gasket [I will need to have some special made in the near future].
I noticed the bike you purchased has the rear coaster brake, also an item that may need your attention. The rear hub has the outer flanges "pressed" on, instead of being part of the actual hub, and the flanges work loose and cause the wheel go "limp". The spokes affix to the outer flanges, and when they work loose the spokes no longer hold the wheel together. A simple visit to a bike shop and have them replace the hub with a quality unit is the long term cure. During the visit to the bike shop you might also want to replace the original tubes [I have had many split at the seams] with the thorn resistant versions for safety reasons.
It is important to note that my infromation isn't intended to "bash" or "discredit" anyone, or any company, just want everyone to be safe and enjoy owning a Whizzer.
Have fun,
Hope this information is helpful