Disclaimer: someone on this forum might know better than me, so do speak up.
I think there is something other than fuel in the fuel tank, and it gets stirred up when you put fuel in. I don't know if
- it clogs up a filter near the tank, and the engine is starved of fuel, or
* something unpleasant has to work it's way through the whole engine.
I think you have to get all the fuel out of the car, pipes and all. Clean or replace the fuel filter. Flush out any mud, grit or tar. Put it all back together. Be careful where you buy petrol.
You will probably end up with a lot of suspect fuel. You could shake up some of it and put it into a tall glass, and see if any mud falls to the bottom. You might be able to put it through a filter and use it.