i have the tower hobbies st-15 and has been running fine until yesterday..the car bogs down when i give it a bunch of gas. is my motor out of tune? also, it dies about half way through a tank of gas...do you think the motor is over heating?

The bogging out (at high speeds) sounds like the High-Speed-Needle (HSN) is too rich. However, if that makes it worse it could also be not getting enough gas. The dying at half tank sounds like its too hot so after it dies wipe a couple drops of spit on the cooling head. If it boils away in under 4 seconds its too hot. But if after 5 to 7 seconds it is still wet then your good. If it's too hot (and your high speeds isn't working-as you said) then turn you idle and Low-Speed-Needle down however if it is still cool after dying then it is flooding and richen it up.

P.S. Sometimes...right before it dies... if it goes really fast it is over-heating and if it bogs, "chugs," or pulses it may be flooding. Just a quick way to know what to tune!