Well, I'm not too sure about biodiesel, but my Fourtrak (2.8 non turbo diesel) runs without any problem on 50% fresh veg (rape) oil with no other modifications.

I guess it should run ok on 100% biodiesel as I thought biodiesel was a direct replacement for dino diesel:

According to http://en.wikipedia.org/wiki/Biodiesel

"Pure, non-blended biodiesel can be poured straight into the tank of any diesel vehicle. As with normal diesel, low-temperature biodiesel is sold during winter months to prevent viscosity problems. Some older diesel engines still have natural rubber parts which will be affected by biodiesel, but in practice these rubber parts should have been replaced long ago. Biodiesel is used by millions of car owners in Europe (particularly Germany)."

Also,

"Biodiesel is a better solvent than petrodiesel, and has been known to break down deposits of residue in the fuel lines of vehicles that have previously been run on petrodiesel.[17] As a result, fuel filters and injectors may become clogged with particulates if a quick transition to pure biodiesel is made, as biodiesel “cleans” the engine in the process. Therefore, it is recommended to change the fuel filter within 600–800 miles after first switching to a biodiesel blend."

Soon after using veg oil, I had to change the fuel filter, so maybe the above is correct!

1985 Veg oil burning Fourtrak "Rocky".