What compression/gears/convertor/etc are you running? I have seen a lot of cars with big cams and intakes (and the 305 magnum is definately a big cam) that will pop back thru the carb if they have insufficent stall speed in the convertor or too high of gears...no torque and a lot of load dont go together very well. What is your initial/total timing, power valve size, jetting, etc. It could just need some tuning.
'78 chevy truck-355, 9.4-1, vortec heads, XE268, vortec rpm intake, 750 edelbrock, flowtech headers and terminators.
'77 Nova-slowly progressing project.
'78 Nova-parts car?
'95 Lumina 3.4L DOHC 210hp daily driver
[This message has been edited by travis (edited 12-07-2001).]