Trying to start a cold engine, with cold oil in the pump system is hard, the oil isn't viscous enough to spray proporly from the injector, once the eingine is warmed up, the oil "melts" a bit and is then suitable for the injector to use.
I'm running my van on WVO and even with heated fuel lines, the oil that is in the pump when the engine cools overnight, is enough to give me serious problems to start in the morning if i forget to switch back to pump fuel before i park up.
I've been doing the WVO thing for years now, it's great when it's warm, but cold nights mean cold engines, cold engines mean cold oil, cold oil means you can dislocate your shoulder before your eninge will fire!