SDFS3, sd card logging, periodic long delay

Greetings all,
I have a question about writing to a sd card using SDFS3.bas program from MELabs. I'm writing a string of data from an ADC with a time stamp, and delaying between writes. Each line of data is 32 bytes, and every 16th line the write takes an extra 100 ms. 16 X 32 = 512, which is the sector size on the card. Is this delay due to addressing a new sector, erasing the next sector, or something else? Any way to eliminate the delay. Throws off the timing of everything! Any help or ideas greatly appreciated.