Puzzled by loud knocking from engine

Thanks for your addvise and sorry I haven't got back to you earlier, been working like a dog. It sounds like its coming from the number 1 cylinder but cann't make out weather it's top or bottom end. Checked the firing order of the distributor and when the crank shaft pully is lined up at 0 degres the distributor rotor is firing number 4, as an amateur it seems to me to be 180 degees out? Yet there's only one way to fit the dizzy back on, I haven't touched the timing and besides the knocking the old girls running real smooth. Also when inspecting under the valve cover I noticed a few small pieces of what I think is carbon(black grity and could brake to nothing between my fingers) don't know what the hell its doing in that part of the motor? I did do a STP chemical oil flush about 3 weeks ago before changing the oil and filter, prior to the recent works but the noise wasn't present before stating the works. Thanks for your help and much appreciate any ideas as this is starting to do my head in! Cheers