ePub to Mobi - file size leap

[lenz117]

I have an epub file that at 0.7mb that when converted jumps to 3mb. I have played with calibre 0.8.8 with varying results. I am using optimised gif files.
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If I do a straight epub -> mobi conversion then the size increases 4 fold.

I just changed the mobi output settings to generic rather than Kindle and this then created a mobi at 1.5mb - but now cant replicate that on other book files (I have 5 I am trying to publish)

I beleive that when you convert to mobi - epub also gets bundled hence some increase in file size - but 4 times?

I know there was a script to remove the epub aspect from a mobi - but the script I have has no effect with these new files.

Has anyone else had any experience of optimising mobi files - naturally to try and reduce delivery charges for books