Impossible to start machine again ?

I have very strange problem with tempra 1.6 . It have monopoint injection and i use TNG gas too. Sometimes, when i stop machine, next minute it is impossible to start it again. When i look in the monopoint i can see fuel is ok- it comes from some kind of cone in the middle of monopoint and i can smell gasoline. There is the spark normally but i cant start the machine. Than, when i try with fuel pump turned to off (without gasoline-only with remains of it in the monopoint) and with selector turned to TNG-gass, machine starts to work! What can be the problem?

it seems, it was because of too much fuel... few months ago, i had fire near monopoint... fire didn't last too long but slightly damaged wires around ... after putting better insulation around wires (specially around 4pole cord on the top), sensors and injection starts to work properly..