You're sending pulses for 200 microseconds, each pulse 26 microseconds, so that's 8 pulses. You then similarly delay for another 200 microseconds afterwards. From the Vishay datasheet: "After each burst of length 6 to 70 cycles a gap time is required of >= 10 cycles". Per the spec you need more gap time.
Grumpy_Mike:
Have you checked the frequency you are getting from the transmitter? You need a scope. Any miss match in frequency is going to affect the receiver's sensitivity.
I didn't really investigate it but in my experience I never noticed any difference in range due to frequency mismatch. Putting that another way, I built 8 transmitters using 555 timers and only bothered to set the frequency initially and never noticed any difference in range between my transmitters. Towards the end of my builds I was setting the pot for frequency adjustment simply by estimating and was still getting the same results.