Assuming this rig sat for 6 months, then the fuel would be bad and the carborator likely gummed up a bit.
Since the carb was acting up 6 months ago, then it probably has other issues.... and it's almost 30 years old. Unless this PO let it sit a lot with old gas in it. If this were the case, I would double or triple treat the gas with Seafoam or some other good fuel system cleaner and see what happens after an hour or so of driving.
As far as the fuel filter, yes it could have some bad gas in it, but so would the tank and fuel lines. Since it's only 6 months old, I seriously doubt it would be plugged up. However, fuel filters are cheap and isn't a bad idea.
John & Clare - Buck & Zeus - Jack & Husky
2008 Fleetwood Bounder 38P
Towd: 2 HD Streetglides