The flame trap itself is a small black canister about 1 1/2" long, with a small perforated insert inside. It is usually mounted very inconveniently about halfway down the inlet manifold, just above the oil separator. They are often neglegted because so fiddly to get at. A useful modification is to get some longer hoses and re-position it on top of the manifold. Then you can easily pull it apart and clean at each service.
The small pipe to the inlet manifold is very important, together with the brass nipple it fits on. The restriction hole is very small, so easily clogs up remarkably quickly. It is an important part of the crankcase breathing system, and affects engine running too because of the pre-determined quantity of air sucked in all the time.