If it runs with the choke on, and then- just won't with the choke off,, gas flow is restricted..
Try replacing your current 2 stroke oil with 100 percent synthetic 2 stroke oil. Available at any motorsports dealer. Worked for my Razz. Has not smoked since.
If gas is leaking from a Yamaha Razz muffler, then the float may not be set correctly. This means that it is not shutting the intake off.
2 places
Here's a link for the Razz repair manual-http://www.mediafire.com/?xibwfty2mtj
Yamaha Razz Service Manual (found through Google and another WikiAnswer question) http://www.mediafire.com/?xibwfty2mtj Also available at http://scootertime.net .
.039-.043
There are several reasons why a Yamaha Razz may quit running. These include issues with the engine, its age, issues with spark plugs, lack of gravity, lack of oil, lack of gas, etc.
http://www.scootertime.net/viewtopic.php?f=39&t=954
Does it run on choke? Is it starving for fuel, if so is the needle valve set for the float?
Bad needle/seat valve on carb.?
10th digit of VIN is always model year; use common sense to determine decade.
It can go upto 45km per hour depending on weight and weather, which is about 72 Km an hour.