Delay of four characters using CBREAK mode on RS/6000

[Robert Lupton the Good]

I have some code that runs on lots of machines and reads keystrokes
in CBREAK mode, using a BSD-style tty driver. Compiling with 
	c89 -D_POSIX_SOURCE -Dunix
I get a delay of 4 key-strokes between when I type a character and when
my code sees and echoes it.

Any ideas?

				Robert