Well Lynx is on the right track indeed, But how many tanks have you put through it. Less than 10 I guess. When you are breaking in the engine you don't want the shell on and you should be doing it on level asphalt (Tarmac etc) so you don't over stress the engine. It will cut out if you leave it for a while idling, as lynx said it is just loading the case with fuel so eventually it hydro locks and stalls. a way around this is to trim it with a little throttle, don't adjust the radio, just use the radio trim. When you start tuning it only adjust the LSN, when that is set to how you want it then you can set the HSN. There should be no need to play with the MSN as this will upset everything and you'll start having nightmares until you get lucky and find it's point again.