The Universal Atomic 4 is a gasoline engine that, though out of production for many years, still powers a large percentage of sailboats.
Check out the Atomic4FrequentlyAskedQuestions. Also, check the lists of Atomic4PartNumbers, Atomic4Mechanics, Atomic4PartsSuppliers Atomic4EnginesForSale and Atomic4PartsForSale.
Eric Haberfellner C&C34 site has some manuals, and the parts list.
Captain Ron's Atomic 4 page includes a copy of the little owner's manual that came with the engine.
Robert Hess' history of the Atomic 4 Hint, it's not a jeep or tractor engine.
Theodore Enders describes adding a High Temperature Alarm
Sea Magazine has an article describing a tune-up online
A parts catalogue showing most of the atomic four engine parts and description of them is available in PDF format at http://www.pearsonvanguard.org
The Atomic 4 owners manual and repair and maintenance manual, in PDF format ftp://ftp.sailnet.com/tartan/Atomic4/Manuals/
Don Moyer has lots of information on his web site.
Be sure to check out http://www.alberg30.org/maintenance/MechanicalPropulsion/Atomic4/ and http://www.alberg30.org/maintenance/MechanicalPropulsion/Atomic4/updates.html too.
A catchall page for EngineRelatedInformation.