Motorcycle Repair: 1989 yamaha riva 200 carb problem, yamaha motorcycle, accurate diagnosis

Question
I have been working on the above scooter and the problem is you can start and ride the bike but it runs perfect up to about 2/3 throttle opening and when you get to that point it quits if you roll back on the throtle it will start running again the carb has been cleaned and reassembled properly several times but performance is the same. Any help please I am not new to the business,but this one is it. It has been to three yamaha shops before me.Any help .I am considering installing a different carb .Is this a normal problem with the 200's Thanks a lot in advance.  

Answer
Hi Ron,

It's not common with any Yamaha motorcycle or scooter.

I suspect one or more of the following: the main jet is not the correct size, fuel supply restriction, fuel service limit out of specs, or other.

Unfortunately, I would need to be present and inspect the problem to offer an accurate diagnosis.

I may be able to help if you could send me images of the carburetor internal parts.

Respectfully,
Mark Shively