FPS Issue in iPhone4 iOS 4.3

I am testing a build/app on iphone4. The FPS of my app is dropping down to 10-12 in iOS 4.3 but it is running fine(35 to 40) on iOS 5.0
Can anyone suggest what can be the reason?

Are you running on simulator or on device?

I’m running my game on device one with iOS 4.3 and another with iOS 5.0.

Just for more info, if i comment particle system and progresstimer used in my game fps on iOS4.3 increases to 25-30