There are several reasons that you could get that incident.
I had the same issue on my A600 but it turned out my 3.1 kickstarts wasn't the correct. Also the speed of the EPROM is important.
I had same issue in an AMD 27C400 that I tried on an A500 and a normal 3.1 kickstart that only gave black. After burning it on a Toshiba 27C400 it worked like a charm.... Go figure :S
Also, have you doubled the 1.3 Kickstart (since it's 256KB)?
You need to just:
C:\> copy /b kick13.rom+kick13.rom+kick31.rom DualKick.rom
...and then Byteswap the image in an programmer and burn.
Then you need to raise EPROM's Pin 1 and tie it to either GND (for lower bank = 1.3 Kickstart) or +5V (for upper bank = 3.1 Kickstart).
If you put it on a 3way switch... make sure that Pin1 goes to Middle Switch Pin while the other Switch pins go to +5V and GND and you're set
