PTT problem

Hello list,
I'm new to packet radio and am not as good at circuit design as I should be!!:)

I've built a circuit to interface the serial port RTS signal to the radio PTT line.
The radio is an old ICOM IC-20 and I checked to make sure it has a positive voltage (+12V) on the PTT line . If I ground the PTT lead, it keys the transmitter, so I think the radio is working correctly.

The circuit I built uses an opto Isolator (NTE3040).
I tried to send the circuit lay-out but the server rejected my message...

When I check the current flow on the PTT side of the opto isolator with the computer trying to key the transmitter, I see about 14 mA and the transmitter on the radio does not operate. If I just connect the PTT line to ground through the ammeter, I see about 125 mA and the transmitter does send. Is it possible that the opto isolator is presenting too high a resistance and there's not enough current flow to activate the transmitter? If so, how could I correct the problem?