You're more than likely sucking in air through the oil pump since you don't have the nipple plugged after you removed the oil line. Plug that up with vacuum cap and see how it runs. Also, if you're not using the oil pump and premixing instead then you should remove the internal gear that connects the oil pump to the transmission and reinstall the pump without it. You can also remove the entire oil pump and install a block off plate. Make your own or buy the one they have on Treats.