I sold this last winter.  This is a log of the fun I've had with a 2002 Yamaha BWS-R scoot.  Don't hesitate to contact me if you have any questions.  This is the version just before the "Bug-eye" models.  Unlike prior models there are no speed restrictors to the CDI, or variator.  It also has higher gearing than models from a few years ago.  Top speed is about 70km/h as indicated on the speedo (You know that most 2 wheel motor speedos are optimistic about 8km at speed. Right?)

Basic Tuneup Specs
Plug - NGK BR8HS 0.5-0.7mm (B8HS to BPR8HS works) - 1/4-1/2turn past finger tight or 20 Nm (14 ftlb)
Transmission - 10W30 0.11L when only drain hot, - torque drainbolt 18NM (13ft lb)
Tires - 15f/18r psi for under 200lb.  15f/21r psi for over 200-335lb max
Fuse - 7A cylindrical style
Gas -  Best to use 89 octane or higher especially if run hot. ~80mpg
Oil - 1.3L injector lasts about 500km
Air filter - reuseable foam element. Use the injector oil.

Reference Sources and Suppliers
Yamaha USA's website has PDFs of  owners manuals for free.  Parts diagrams are also found there.
www3.telus.net/dougsimpson
www.mototek.com
www.mopedhospital.com
www.badmotorscooter.com
www.taffspeed.co.uk
Yahoo Groups - BWS Zuma group, pre-bug group

Initial Impressions
Costs
Purchased for $1500 used with 4800km.  I thought this was pricey because my last car cost about the same and my first 50cc scoot cost a bit over $500.  Insurance including $2million liability, theft/vandalism, ownership transfer, GST is about $450 (chop about $100 for reoccurring insurance).

Used bike check-over
Check brake operation - Front is hydraulic disc, rear is cable drum.  Don't start it before trying these.
Check injector oil level - It's under the seat.  Run it dry even for a few moments and say goodbye to your engine.
Check tires - Everyone knows this.  Pressure, cracks, bulges, oil spills?
Start the thing - Use the kick starter if the battery is dead.  Starting requires rear brake applied, choke on for cold.
Try the cutoff switch - Before you even run the thing make sure the cut-off works in case the throttle jams.
Straight run and brake - Check for suspension damage by making a straight run and brake.  Damaged bikes pull to sides.
There's more but these are the basics.

Riding
The BW is quite fast for a 50cc scoot.  Compare this to the Honda Spree I had which had a top speed of 50km/h in full tuck on flats, and 35-40km/h on hills.   I can ride this up steep hills at 50km/h and moderate hills at 60km/h.  On flats in moderately tucked position I can reach 73km/h.  The disc brake is more than adequate but the drums lock easily in the rain because they are more difficult to modulate.  The acceleration in stock form is decent.  Don't expect to drag motorcycles but it is quick enough to surprise most cars.  One thing I've noticed is some car drivers seem to think I'm dragging them.  This is probably because of the quick initial acceleration and the exhaust note.  Dude, you're awesome.  You just out gunned a 50cc scooter.  Usually I see them at the next stoplight. :)   Riding in the rain is ok.  Like most scooters the front shield keeps your shoes and lower pants dry.  If this thing had a higher top speed of about 85-90km/h it would be great for day trips out of the city.

Maintenance and Modifications Done
- Drained old dark tranny fluid and refilled with 110mL Mobil1 10W30. (15 minutes, $7)
- Replaced nearly finished stock front disc pads with EBC standard (15 minutes, $40)
- Replaced old plug.  Tan coloured deposits is a good sign of correct jetting. (10 minutes, $6)
- Drained cloudy anonymous injection oil and refilled with Belray Si-7 (15 minutes, $13)
- Replace drive belt at 5200km.  OEM one ($40) See the photos
- Replace exhaust pipe with Leo Vince SP3 See the photos.  Initially, I ran with the stock 6.85g variator rollers.  This gave a slower than stock acceleration from stop and similar top speed.  4.3g weights were swapped in because the manual recommended it (the photos.)  The acceleration with this was odd.  The starts were high reving and made much fan-air noise.  The medium-top end acceleration slow enough to feel dangerous.  3x 4.3g and 3x 5.8g rollers were used and this finally produced the desired result.  The acceleration is back to normal but the top speed is now past 80km/h.  The exhaust note is a lower tone than stock and has less of the "splat, splat, splat" sharp noise.  It is more pleasant on longer rides.