Starting issuea RE C-350

Hi, I have a C-350, recently there appears to be a starting problem. It's actually the stage after starting, so after the vehicle starts and I let it heat for a minute or two. The problem is after I put it in first gear the vehicle switches off like it does when you ride without fuel. But there's fuel and moreover if I'm riding over a speed breaker I have to accelerate almost 3/4 or half so the vehicle doesn't turn off. You can the change in sound when I accelerate slightly Any ideas that might have caused this or other RE people have experienced this?