I've been running my Carby XF on LPG for a long time now, and I have ran out all the petrol that was in the tank from 6 months ago. I thought it was because of this poor petrol that my car didn't run well on petrol. It runs fine on gas. Anyway, I put in $10 of BP Ultimate today, and turns out its still bad. Idle is screwy and it smokes shockingly, thick black smoke. Good power though. If its anything thats expensive to fix, I'm just going to leave it and run it on LPG all the time as I have been, but im hoping that its just something simple like the idle mixture. But I can't find the screws to adjust it. If someone could give a good explanation or pic of which one it is, it would be a great help.