The problem you are having is that the flash needs time to recycle after a full discharge. What you need to do is either move closer to the subject so that the flash does not have to discharge at full power to expose the subject properly or bump up your iso or use a larger aperture or a combonation of all three.
The usual recycle time of a speedlight is somewhere around 2-3 seconds you can speed it up by getting a battery pack that goes with the speedlight which could drop the recycle time to 1 second but still if you have a fast action scene and need to burst 3-4 frames off the best thing is to make sure the flash is not shooting at full power.
Also be careful with shooting too much in burst with a flash as they can overheat.
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Rex K
The view from my "office" doesn't suck. 
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