Check your power piston, it should move up and down easily. Try lubricating with silicon spray lubricant.
There will be a relief hole somewhere on the side of the pump well. Try spraying lubricant into the relief hole.
The aisan power piston works using the carburetor vacuum. At idle the vacuum is at it's strongest which pulls the power piston up off of the power jet. This cuts off the extra fuel.
As the engine is powered up the power piston starts dropping, pressing against the power jet allowing extra fuel intot he main fuel supply.