am i hearing detonation, pinging, or backfiring?

[1jimmy__d]

Can't tell what this is. here is what is happening:
when cold mostly- i accelerate I hear a popping sound like pop-pop-poppop-pop. if i let up a little and steadily accelerate, it will not do it, BUT i can tell that it wants to. it does it rhrough 1st and second mostly. i have to bring the rpm's up high before shifting or it will do it more in the next gear. it does it mostly in the lower rpms- basically low rpms. my last tank of gas was regular, but i just put in super and it did it today as well. timing is set at just under 13 i believe. I THINK WHEN THE CAR WARMS UP, IT RUNS FINE, BUT HAVENT DRIVEN IT ENOUGH THIS WEEK TO BE SURE. what can i do? thanks-

PS
IF ANYONE CAN GIVE ME A NUMBER I CAN CALL FOR A SPEEDO GEAR FOR A 90LX WITH 3.55'S I WOULD APPRECIATE IT! CANT FIND THE RIGHT ONE ANYWHERE!