hi folks. i have run into a snag. i just put a new 600 holley carb on the 318 in my 74 roadrunner and i have run into an issue that baffles me. the carb will not idle down to anything less than about 1000 rpm. the motor has an edelbrock sp2p 318 intake on it and i added this brand new out of the box 600 holley to it. the idle screw on the side is completely backed off,the timing is set at 10 degrees initial,and to get it to idle down,i have to have the mixture screws on the metering plate jacked so far in,that the car runs terrible. you can actually grab the throttle arm and physically pull it forward and it will idle down,but it takes more force than the return springs can provide. and i have double springs on it now. there are no vacuum leaks anywhere,and i have checked everything. throttle liinkage has plenty of slack and the detent slide is not binding. even took the carb off,took it back and got another new one. car runs great otherwise. any help would be appreciated.