Break-in went smoothly. I used Joe Hubbard break-in oil no problem. The carb just ran a little rich even with the eldelbrock carb switched to a sumitt brand still the same. The carb was running rich after break-in. I just started to drive it under load since removing the motor del my project car to my truck. Three days under load is when the backfire through the carb happened. Started back up then the sputtering started. Looked at my plugs all of them are black and these are new plugs.