been making bio for 4 yrs + now and about to try it in a p38, only had a prob once with citroen van, cheap french piece of ****e!
no need to buy any kind of anyones processor, look up gl processor and take yer time, at least you will know its made properly. never buy one from ebay!!!!
venturi's easy enough too, it's all about reading the instructions properly several times before attempting to build.
mine cost about 300 quid using brand new parts and has saved me many thousands of pounds. you can make them on the cheap using second hand bits, but why would you?
vegetablebiodiesel.co.uk is a good source of info but some of the clique on there have thier heads up thier arse, take what you need info wise but cross them and they will bite!