OK, I've been thinking about his all day and have done some research, so I am going to express a much stronger opinion, and I understand that some may not be comfortable with it. I'm OK with that and I'll tell you why.
I believe very much in all of the Experimental aviation we do. However, sometimes there becomes enough data that points to a potential safety problem. I have spent the last year chasing down everything I could thing of that could be wrong with my engine, because others on this board, and even certain suppliers, stated that no one else is having this problem, so it must be me. I had occasion today to get some advice from "old-timers" who claim that this setup was tried 30 years ago by a number of them and they had nothing but coking problems, so they all removed them.
Looking back, I think one of the differences is not with my "setup" but the fact that I fly it A LOT. I fly 200-300 hours per year, and take long trips like this current trip to Alaska, where we will put 50+ hours on it. I believe I am seeing things that ALL of you with this setup are eventually going to experience, and that is coking within 30-50 hours. There are already a few of you in this thread who have reported it.
It is true that we are experimenters, and I also believe the axiom that "we stand on the shoulders of giants." It has become clear to me today that some of the giants have already had bad experiences with this setup.
Here's my concern for those of you running this setup, especially without a safety valve. With a lot of local flying, 1-2 hours at a time, maybe 20-30 hours per years, you won't see this issue rear it's ugly head until you decide to take that long cross-country to OSH, to the Bahama's, or to Alaska, where you will very quickly add the 20-50 hours where the coking WILL show up. Without the safety valve, the odds are you could have a very serious problem before you catch it, including a blown nose seal and the commensurate loss of oil pressure.
No, there is nothing wrong with the valves. There is most likely nothing wrong with the air/oil separator (I don't even have it installed this time. I have duplicated the problem with and without the separator). This is a problem with attaching the output of the breather tube to the exhaust system. And yes, Dan, mine is aft of the muffler on the RV-10.
Against my best judgment I made this change again before a long trip to Alaska. I broke my own rule of no changes at the last minute, but at least Dan's safety valve worked. Someone must be looking out for me. So I feel obligated to pass along the experience and the warning. Please heed them.
Vic