It seems to me that the output level of your transmitter is too low. The printer port will normally require signal levels of 5V to work correct. Try the following:
100K
|-------------------/\/\/\------ pin 16
|
| c
| 2K2 b /------------ pin 10
Signal ------/\/\/\------|
\------------ pin 18
e |
Ground ----------------------------|
Transistor 2N2222/BC109 etc.