Need Help on my Hatch

I have a stock motor on my civic a d15b1 and i did the
oil change and the oil filter and it was running fine but
when i switch from first to second the car backfires
does anybody know what can i do to fix that

Could be a bunch of things. Just don't get too freaked about it start from the smallest (cheapest) thing first. Check the:
-Fuel filter(s)
-Fuel Injectors
-Clutch cable
-Timing Belt ETC...
My 90 was doing that but it would not even start. It would just backfire. turned out to be my distributor. GOOD LUCK!!