The age of the fuel is a consideration as it degrades quite quickly now. Ninety days is considered the shelf life for todays gasoline. Beyond this, checking the engine vacuum with a gauge would be advisable. The vacuum reading needs to be a high steady reading at idle. If not steady, then checking the spark plugs, timing, and performing a compression check helps. And don’t rule out a vacuum leak either at the intake gasket or any of the vacuum driven accessories. And of course there’s the carburetor which could simply need the air bleeds cleaned or the fuel mixture screws readjusted.