This was a tip I found on the RCU Reviews by their expert. I checked with the OS support forum and they confirmed it. We used this on both a 120 and a 160 and got them both to run great. With both tubes open neither would allow the mixture to set correctly. I know some people have been able to correct this problem without closing off one tube but the majority of folks I've talked with on this have found this to be the only way to correct the problem. I'm not sure why but I know it worked for us. May have something to do with altitude (we're at sea level) or just a slight difference in the engines but OS states that you should never replace the muffler with one that has a larger opening then the stock muffler. Slimline corrects this by putting baffles in their mufflers. He may have a different problem altogether, I'm just letting him know that this could be the problem in case all else fails. BTW I have seen Whaturi's video, very impressive. I run a APC 18x6W on mine and get 9000 rpm and 18 lbs of static thrust on the ground.

http://www.rcuniverse.com/magazine/a...article_id=262