not getting the power I thought I would get !

[adamrc29]

its a 67 mustang coupe ,c4 trans the compression is around 9.5 , this is my first dp mechanical secondary carb I have ever run , im use to 600 cfm vac-sec. , and I did set the float levels to were the fuel just trickles out the side the air fuel is set 4 turns out , I have a suspicion its the crane xr-i it ran close to what it should be running after I set the carb a little rich, it ran strong through the gears and a few minutes later I stepped into again around 3,000 rpm in low2 and it spuddered just like a rev limiter had kicked in I swapped off a set of wires too and it didnt make any differance , its like it performs good one minute and runs like shit the next .