I've got a 1974 260Z with the 260Z head on a 280Z engine block. what I can' figure out is why it won't run right. I can't get it to stop bakfiring and it has lost all low end power. I got the car with this enigine configuration and it ran fine for about 2 months. Could swapping the carbs help. Any help that you guys coul give me would be greatly appreciated. Thanks.