Weird stuff with D24 engine
 

I began doing engine refresh for my D24 last week and I just adjusted the valves for it and I am putting the car back together.

I'm also making headers for the engine and my worries began when I did a test start with a test header pipe today which included the mounting plate to cylinder head and a small pipe from each cylinder.

So when the engine idled it sometimes sparked from one of the cylinders. The spark was very clear and it sparked when you touched the throttle especially.

Is the sparking just buildup burning and coming out of the headers?

Also the engine was running kind of rough and I just changed the injection pipes because they were leaking. Do I have to bleed each pipe to get the fuel to run through them?

Could be. Other possibilities: Overfueling, incorrect injection timing.

Normally it takes quite a while of cranking to bleed empty injector hardlines. Once the engine starts they finish filling up quickly when running.

Small flakes of carbon disturbed in the exhaust will exit as a spark