Yeah, I tried the screwdriver/piece of vacuum line trick and I still can't determine the source. It sounds like the top end to me. I adjusted the valves and no change. I didn't see anything abnormal while I was in there either. it sounds too high pitched to be rod knock but sometimes on start up it dose knock until it builds oil pressure.
One thing tho, when you put a finger on each valve cover bolt, the front one on the intake side has a noticeable taping in it. It could just be feedback from the mec-fuel pump as it makes quite a bit of rattle on its own.
The engine has a fairly new rebuild with only 15k on it so it shouldn't be the chain or guides but I'll check anyway. The sound started when I was snow wheeling and was revving her pretty high.
I've been wanting to put a slightly bigger cam in it so maybe I'll start there.
