Any change in induction length/pressure can cause problems. The cold start is calculated on airflow which SHOULD go into the engine not what actually is going into the engine. What I mean is the coldstart is set at the factory using standard induction, if you try and improve that when the engine is up to temp it will effect it when on coldstart. And when you say it feels like its running out of petrol I take it you mean you open the throttle and you get a "burrrrrrr" sound and the revs drop? If so this sounds like too much air or not enough fuel, just like if you pushed the choke in too early on a carbed car. I would take it back and see if there is anything they can do on their kit to help, but if you gain driveability when cold you may loose performance when hot.