Horizon starts but won't catch

My husband is trying to help a friend of ours whose Horizon will turn over but not catch. Our friend is broke and we're not far from it. We towed it to our house and my husband has recharged the battery, made sure it has gas in the tank, cleaned the plugs, says the carburator and what all else is getting gas, the plugs are firing, he's cleaned the distributer cap and rotor (I am not very well versed in this stuff). The oil level was very low and dirty but my husband says it shouldn't affect its ability to start. Does anyone have any experience/suggestions? We'd be most grateful. THanks. Ellen

have him do a compression test and make sure the compression is not off or low. Bad cylinder compression will give you the same problem and that could be the result of a blown head gasket.