A cold engine needs a richer fuel mixture. If your accelerator pump isn't up to snuff the stumbling (burp) will be worse with a cold engine. The vast majority of cases of this type of problem I've experienced have been the result of a faulty accelerator pump.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.