I found, in Franklin's autobiography, his personal thoughts on the controversy.
Samuel Hemphill was the kind of preacher Franklin appreciated most. Rev. Hemphill already got in trouble with the orthodox folks in his community for his "heterodoxy" and Franklin defended his heretical theology against a theological lynching.
Bad as that was, Rev. Hemphill had another controversy with which to deal and against which Franklin also defended: He apparently plagiarized one Rev. James Foster, a fellow Arminian unitarian, universalist, heretic. Indeed, arguably Rev. Foster was the source of Hemphill's heterodoxy.
Here is Franklin on the matter:
About the year 1734, there arrived among us a young Presbyterian preacher, named Hemphill, who delivered with a good voice, and apparently extempore, most excellent discourses, which drew together considerable numbers of different persuasions, who joined in admiring them. Among the rest, I became one of his constant hearers, his sermons leasing me, as they had little of the dogmatical kind, but inculcated strong, the practice of virtue, or what, in the religious style, are called good works.
Those, however, of our congregation, who considered themselves as orthodox Presbyterians, disapproved his doctrine, and were joined by most of the old ministers, who arraigned him of heterodoxy before the synod, in order to have him silenced. I became his zealous partisan, and contributed all I could to raise a party in his favor, and combated for him awhile with some hopes of success. There was much scribbling, pro and con, upon the occasion; and finding that, though an elegant preacher, he was but a poor writer, I wrote for him two or three pamphlets, and a piece in the Gazette, of April, 1735. Those pamphlets, as is generally the case with controversial writings, though early read at the time, were soon out of vogue, and question whether a single copy of them now exists.
During the contest an unlucky occurrence hurt his cause exceedingly. One of our adversaries having heard him preach a sermon, that was much admired, thought he had somewhere read the sermon before, or at least a part of it. On searching, he found that part quoted at length, in one of the British Reviews, from a discourse of Dr. Foster’s. This detection gave many of our party disgust, who, accordingly, abandoned his cause, and occasioned our more speedy discomfiture in the synod. I stuck by him, however; I rather approved his giving us good sermons composed by others, than bad ones of his own manufacture; though the latter was the practice of our common teachers. He afterwards acknowledged to me, that none of those he preached were his own; adding, that his memory was such as enabled him to retain and repeat any sermon after once reading only. On our defeat, he left us in search elsewhere of better fortune, and I quitted the congregation, never attending it after; though I continued many years my subscription for the support of its ministers.