jQuery.post

Hello,

I guess I figured out the problem, but I somehow can't solve it.
I try to POST an base64_encoded image via ajax. As long as the image is small, it works perfectly, but as soon as the image gets bigger, it fails, though jQuery fires success and no error messages appear.
I already watched my php.ini and the post_size_limit is set to 2GB.
Does any one has an idea how to solve this?

Thanks