I have a zetec fitted with zx9 carbs however I thought i was down on power however today when i was playing about i noticed that when i rev the car the piston inside the carb is not moving, any ideas?, the butterfly is moving and i have checked the top cover and greased before put back, im not sure whats at fault

Check it's not sticking and check the diaphragm for splits.

Stu

Also check the plastic cap / carb body seal

I've checked and found no splits, don't think the tops leaking, I've put grease around the rim to check for a good seal