West bend 100 idles on only one cylinder

[threswiftri]

I've got a West Bend (model 10482 / don't have a clue what year it is ) that when operating at low idle only fires on one cylinder. At high idle it fires one both cylinders with no problem except, a while ago it would only fire on one cylinder at high idle so I replaced the plugs and it fired on both cylinders at high idle again. Still won't fire on both cylinders at low idle. Would this likely be a compression problem, ignition problem, or, carbrator problem? Thks!