While it is true that exhaust leak can cause this it is not always the culprit. The intake needs unobstructed air flow and sometimes "critters"
Hi y'all...yup she's a knocker...idles ok...starts ok...just seems to knock substantially more than any other 2 stroke I've ever owned. At the lower RPM's
Maybe you can download the operator manual or someone here may chime in. Just looking at the parts I would pump the primer twice and try and start it
Keep asking how and someone will guide you thru it.
You came to the right place ! These guys know their stuff! I have the dame motor, just a few years newer