Wrong cap , it possibly should also be yellow also with an oil can symbol on the top
That is a fuel cap almost exactly the same as a couple of Ryobi I have , minus the holes
Have you checked the breather hose that runs into the air cleaner ?
https://www.ebay.com.au/i/1436467772...SABEgKHzfD_BwE
That is the cap I mentioned
Oz