While the Robins defence has started solidly, conceding only four goals in six games, the strikeforce is stuttering on just five goals in that time.
"We've created a lot of chances but our conversion rate has not been particularly high," said Sinclair.
"It's not just the forwards' responsibility however, our midfielders have had opportunities and we need to start capitalising on attacking set-pieces too."
The winner over Casuals was scored by full back Ricardo Panton via a powerful header early in the second-half, while striker Kingsley Aikhionbare got the consolation against the Terrors.
"We played better against Worthing and lost to a goal which came completely out of the blue," Sinclair added.
"We didn't play as well against Walton but got another three points. These things happen in football from time-to-time but I feel we'll be due a big win sooner rather than later."
Carshalton play their first FA Cup tie with an away game against Mole Valley SCR on Saturday.