Greasy beast, I'm sure you've got a bad IP. I had exactly the same problem. Was very surprised to see two others (you and Pat Cain)with this problem of running great on veggie but not idling and very hard starting and power loss while on diesel. Pat said his problem was solved by replacing the IP. My symptoms started happening after running a tank of veggie that had probable water contamination. The problem was not air in lines or plugged lines/filters as one would at first think. I tried timing the IP, set valves and valve timing, etc. Replace the IP with a junkyard one and problem was instantly fixed. Power was back, idled like it used to on both diesel and oil and started just fine ever when hot and on diesel. Old IP had damage to ALL cylinders probably because of water injestion and was not pumping proper pressure when on diesel but with thicker WVO worked fine. Very hard problem to diagnose but I am 100% sure if you try that old IP you have in the junker out back the problem will be fixed. Now I've got to find a way to make sure no water is in that WVO as it seems to kill the IP right quick!

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'84 300SD, '87 300SDL, '81 300SD