I bought a used 85' moto 4 200 recently. Would not run correctly or start. Rebuilt carb and I believe all my settings are correct. But it wount start or run correctly unless I hold my finger over the inlet of the carb covering the two 1/4" holes. Which I can feel a strong vacuum coming from. When I do this it starts and runs perfect. But otherwise won't start or run properly. Any expert advice.

 

sounds like the main jet or pilot jet is too big. double check the numbers on the jets to make sure they were the right size

 

Thanks for trying to help. But, I finally figured it out. I had missed a very small jet that is in the bowl when I rebuilt it. I also realized that the new 3" throttle needle was longer than the original so I put the original back in. The combination fixed all of the problems.