I am running my 1990 Suburban 6.2L on waste vegetable oil. I do a cold start-up on petrodiesel and switch over to oil when engine is up to operating temp. At the end of the day, I switch back to petrodiesel and purge the fuel line of oil so that in the morning I can start up again with diesel. When I first completed the conversion, the engine ran remarkably smoothly on the oil, but occasionally there were little rough spots. I read that even if your engine runs well on petrodiesel, dirty injectors may cause a rougher ride when running on the oil, and also that advancing the timing slightly will help with oil combustion. I had the injectors cleaned and the timing advanced, but there is way too much 'clacking' noise now, and I have not noticed that power or performance on the oil is any better. I cannot stand to drive the vehicle with that much clacking. I am new to diesels, and I want to learn to fine-tune the timing myself. Is it as simple as loosening the 3 screws on the injector pump and rotating it slightly in a trial and error approach? Are there any other things I need to consider? (I read somewhere that one should not adjust the injector pump with the engine running). Also, does the engine need to be warm? Any help is greatly appreciated. I am happy to share any information on WVO and biodiesel (I run B20 in the factory tank) to anyone who wants to know more. Many thanks.