340 lifter noise

I recently bought a 68 340 dart that had been sitting for several years. It ran fine but had a slight lifter tick at idle so i replaced the lifters. The cam showed no signs at all of wear so I didn't see a problem. I bought the lifters at NAPA and bled them out before installation. My problem is, when I start the engine after it has sat for even a day, The lifters clatter for a few seconds and then shut right up. The motor runs great after that, any ideas?:oops: