I have bought the following bing carb: https://www.oldtimervergaser.de/de/bing-vergaser-dkw-nz-250.html Once fitted, it will run for about 2 seconds then die. The main jet is a 2.70 is this correct? It had a dellorto carb fitted, and when I put this back on it started easily and didn't die, so I kno...