Read from what and how do you know there's supposed to be 433 bytes available? Is this a serial instrument? If it is, you should be using the VISA Bytes at Serial Port to determine how many bytes are actually available. If this function says that there are more than 166 bytes available, do you have termination character enabled in your serial port config? If you do and the termination character (by default a LF character) is in the data you're trying to read, then VISA Read will terminate when it's detected.
If this doesn't fix your problem, provide some details on what you're doing. Post an example VI if you can.
