High RPM Backfire when fully warmed

Check your firing order.
If it were a needle n seat.. it probably would wanna die at idle from being drowned in fuel. The factory box .. I quit using those .. something about them pulling timing or duration about 5k.. I can't remember anymore. Is it the 5 or 4 pin?


Sometimes I assume people have the basic **** covered by the time they come here asking for help. If This Were your typical roller, those hughes Springs would not be enough.. but because it is a magnum core with a giant base Circle, the Springs work okay.. or should. Factory valve lift at about .420- .432 or whatever only used 90 seat and 200 open... so should be good you'd think.

Still confused as to where the 901 spring mentioned fit in.. as where you say you bought the Hughes springs, was that after or ... what spring is in the head???