The firm said it had taken steps to improve recognition of "bad links" and detection of Ascii art - drawings created out of punctuation and other characters.
The inclusion of web addresses and art in YouTube posts only became possible after the switchover.
Using Google+ has proved controversial.
An online petition has raised more than 216,000 signatures calling for the comments section to return to its original form.
It objects to the fact that tying YouTube to Google+ makes it harder to stay anonymous since members of the social network are supposed to provide their real first and last names.
That change was intended to combat spam, which the US firm said had "plagued" YouTube for years.
However, some users have complained that by allowing links and art in comments Google had instead exacerbated the problem.
Security blogger Graham Cluley wrote that by allowing links the firm had made it "easier than ever for spammers, make-money-fast-scammers and malware-spreaders to get airtime".
Meanwhile, the Ars Technica news site reported on the rise of what it called "comment pornographers" - people who post pictures of genitalia made out of dots, dashes and other symbols.
One of YouTube's most popular members, Swedish video game commentator Felix Kjellberg, had been one of those who had temporarily blocked comments on new videos as a consequence.
"Front page/top comments are filled with links to virus sites, advertisers, self-advertisers, spam, [and] copy-and-paste pics," the clip-maker known as PewDiePie wrote.
Google said it had now changed the way long comments were displayed, making it harder to show drawings, and promised to offer video creators more control over their viewers' posts.
"Bulk moderation has been a long standing creator request and we'll be releasing tools for that soon," it said. "At the same time, we're also working on improving comment ranking and moderation of old-style comments."
One company watcher said it was important for the firm to ensure the switchover was a success.
"There is the rationale that it will help drive the adoption of Google+, which I think it is fair to say has struggled against competing social networks," said Richard Broughton from the consultants IHS Screen Digest.
"It will also help with the monetisation of YouTube over the coming years.
"Having information about the people who are consuming the videos - thanks to them being linked to a Google+ account - provides an awful lot of information, which is of use to advertisers.
"But making this scale of change to a network that has more than one billion regular users worldwide will inevitably offend or annoy some of them."
Google has acted to tackle abuses of YouTube's comments system that were made possible by it tying the posts to its Google+ social network.