If I recall, someplace in my fogged memory, I remember that the big "K" made the statement to NOT USE BIO DIESEL in your tractor, but things may have changed
I purchased my B2650HSDC last year, and in my owners manual it states that biodiesel can be used under certain conditions. One being more frequent oil changes, and changing the fuel filters more often. It does state that the use of any problems that arise from the use of poor quality fuels that fail to meet the above requiements, whether biodiesel or mineral oil based, are not covered by the Kubota warranty.
I happen to live in Minnesota, the first state to mandate the use of biodiesel. And currently, during the summer months, I can only purchase a mandated 20% blended biodiesel. So unless I stockpile my fuel from times during the winter where I might be able to use less than the mandated 20% biodiesel, if I could find a source that had less than the 20%, I am forced into the situation.
So far I have had no fuel related problems with my tractor. I treat all my fuel with an algicide, and anti-gel in the winter. Hopefully, I don't have any problems.
With regards to how fast my B2650HSDC starts, with proper use of the glow plugs, two to three revolutions and it is running.