I've had this Riva for a few years now with no problems. However, while riding it this spring it began bogging down/stalling while I was riding. I stopped, killed the engine. A few moments later I started it and took off, within minutes it began stalling again. Again, a few minutes rest and off I went. Anyway, now it starts and idles fine, but sputters/stalls out whenever the slightest bit of throttle is applied.
I took it to my local Yamaha shop (a friend works there) he cleaned the carb, checked stator, etc. with no change... NOBODY at the shop had any clue why it did this. He mentioned it could be the BCV (BiMetal Control Valve), the CDI, or a vacuum line issue. He worked on it for several days with no results. After some research on my own, I thought it could be the MCV (mix control valve) or the Auto Fuel Petcock too...?
I'm personally not much of a mechanic, but I LOVE this scooter. The CDI is a $300 replacement and he couldn't guarantee that would fix it. If any of you folks have ideas, I'm all ears.

The bi-metal switch is a known problem with the rivas as well as a over complicated carburetor system they abandoned.

Thanks donny. I'm planing to do a petcock bypass next week, if there in no change, I will attempt a BCV bypass. Once I understand the procedures and acquire the parts needed.

Pretty looking ride.

I'm having same issue: starts and idles well, but when I apply throttle, it bogs down and stalls. By sticking my finger into the carburetor intake while at idle (until I can feel the fuel entering carburetor) and applying throttle, I am able to get it to run normally. This tells me the engine is running lean (not getting enough fuel) at higher throttle and thus stalling. By restricting the air being introduced into the combustion chamber, I am essentially enriching the fuel/air mixture.

vacuum leaks and air leaks possible from old tubing,may try replacing?

If you can stick your fingers right in the carb, it doesn't sound like you have the airbox in place. The airbox typically poses a significant restriction in airflow, so the scooter may run normally with this installed.

If I'm mis-understanding you and you're just sticking your fingers in the airbox intake, then I agree your engine isn't getting enough fuel and an examination of the carb jets is likely in order.