I have a 2002 5.3 with ported 706 heads with ls1 intake valves. Cam is 216/220 with a 111lsa at 601 lift. I can get it to fire off it revs up the dies then as soon as it dies you try to start again it will shot fire out the exhaust. Sounds to me like timing but can someone send me in the right direction in the tune. thanks