@james: correct with the ring gumming, though it shouldn't happen with a twin tank system. If I was just chucking it in the tank or mixing it, then I'd expect this. Interesting what you say about the cylinder temps, don't know masses about diesels. I also agree with the switching over if idle for a prolonged period, but still wouldn't expect 30secs to one minute to puff out smoke.
@reb: the lift pump only pumps the veg oil, so I'm ruling that out at the minute.
@jimmy: what I've read, from those who have been doing this for years, is that this smoking issue we experience often occurs when using injectors that have done more than 60k. He suggests a full service and new nozzles. When I had them checked at the weekend the bloke said they were fine. But perhaps it's worth a second opinion?
Redex probably isn't a bad idea. Next time I'm passing Halfrauds...