Would the USA ever join the Central Powers? Hmm.
The German-Americans were obviously in favour, and most Irish-Americans would support whichever side Britain wasn't on. However, the majority of US public opinion was pro-Britain and France (and Italy, after 1915) - and crucially, I believe President Wilson was strongly anglophile. You'd probably have to get rid of him through an election event to have a chance of moving the Americans towards the CP.
The fact that WW1 was a war of "democracy versus dictatorship" was important for US opinion. (Tsarist Russia being on the Allied side was something of an embarrassment!) For America to line up alongside militaristic Prussia against France, home of Lafayette and the Declaration of the Rights of Man, was almost inconceivable (and would certainly have caused huge dissent).
Germany made some crude errors, but Britain also organised a highly effective propaganda campaign to capitalise on them - perhaps the 20th century's first example of spin doctors at work making sure that the US news agenda followed Britain's lead. (This could be some kind of tech advance?). Much of this was done through nominally independent journalists and authors being given "private briefings" by the UK government, which they then recorded in print. There was also enthusiastic spreading of fake or exaggerated atrocity stories - most notoriously the Belgian Nuns, the Crucified Canadian and the German Corpse Factory.
Finally came self-interest. In crude terms, American bankers and industrialists had lent billions of dollars to Britain at commercial rates of interest, and if Britain went under they'd lose their money. On a more strategic level, Britain and France were "satisfied powers" - they felt their empires were quite big enough already. Germany was out to shatter the status quo and grab a better place in the sun - and if they managed to triumph in Europe, the security of the Monroe Doctrine would look a little shaky...