You don't say if the carbine is GI or by one of the post-war makers; some of the latter guns are not well made.
Misfires are often the result of failure of the bolt to close fully, due to the ammo or a dirty chamber, or (rarely) a short chamber. I would find a gunsmith with Carbine headspace gauges and make sure the chamber is OK before doing anything else. If it is, and ammo seems to be ruled out, the next step might be to replace the firing pin. GI firing pins are available from parts places like www.gunpartscorp.com
. If you decide to take the bolt apart yourself, do yourself a favor and buy a bolt dis-assembly tool as reassembly will be very difficult without it.