I have two questions re my Yamaha TTR50

1. When you reve the engine thier is a delay before the rpms come back down. What could be the cause?

2. Why does the choke always have to be on before this thing will start? Seems even if warmed up, it wont start without the choke on??

Any info would be helpfull

I have two questions re my Yamaha TTR50

1. When you reve the engine thier is a delay before the rpms come back down. What could be the cause?

2. Why does the choke always have to be on before this thing will start? Seems even if warmed up, it wont start without the choke on??

Any info would be helpfull

Both symptoms suggest its too lean with closed throttle, maybe the air screw is too far out or the pilot jet is blocked or fuel level in carb is too low