71 mustang throttle problem.

ok. the cars got headers,intake and acell coil and points kit. ok what happens is that it seems like when the motor gets hot and it's in park and you floor it, it goes up to 4,000 rpm's or so and just stays there. when it's cold and if you rev it up slowly it's fine and goes past 4,000. the only thing i noticed and didn't know if it was norm but the sec's crack open about 1/8th of the way when you punch it. i didn't know if this was norm. the carb thats on it is a holley 3230 which is a modern 4160. i've pulled the carb back apart and cleaned it up and no luck. it's just strange how it only does it when it's really good and hot. the temps only at 190 but less when driving and if your driving it and drop it into a lower gear for speed once it starts hitting 3,500 it starts studdering. i've tried pluging all the vac lines (except the dis) no luck. and the dis is hooked up top the right port for it. i'm running out of ideas. and the power valve is good. my question i guess really is that should the secs crack open like that? i know if i push them open with the motor just ideling. even slow the motor starts shaking and blowing out smoke. and the fuel level in both bowls is fine. right where it should be and fuel pressure is 6-7 psi. any ideas?