I over hauled this mazda va engine a week ago and just started it up now im hearing a load engine knock coming from rear of engine. the engine can be made to run pretty smooth when its cold but it will always sputter and die after about 30 seconds. its running on gas and im wondering if my carb is faulty. When i pull the number four cylinder wire the knocking stops. i pulled down the oil pan and checked the bearings and everything was nice and tight, is it piston slap? is there something wrong with the fuel air mixture that can cause a knock on just one cylinder. as i mentioned , my carb doesnt work real good , i can't seem to get it to accelerate. timing is right to the best of my knowledge, camshaft is new. could be the wrong one ? can anybody please help me with this problem thank you