Glad it worked out for you. I thought about using a dowel to plug one side but decided against it due to the fact that the pipe could hold fuel in the space above the dowel. I just crimped mine about 2/3 to 3/4 closed so this fuel would still be blown out. I run a APC 18x6W on PowerMaster 20/20 and with the engine boken in now get 9000 RPM +. My tank is in the stock location for the GP CAP 232 so that might be affecting your performance. We also did this on my son's OS 120 in his Cermark Pitts with the same results. Prior to crimping the pipe we couldn't even tune the engine. It was like the needle's weren't even connected to the thing. I don't think you need to do this with the SlimLine mufflers as they have internal baffles that create the back-pressure for the engine. Glad it helped you out! Happy flying!!
ORIGINAL: GMoneyPit
You know Lou55, I ignored the advice you give for quite some time. The reason I ignored it for so long is because everyone kept talking about the loss in RPM due to the restriction in the exhaust. I said screw that, I want all I can get out of the engine. But, at the same time, I didn't want to tap the backplate for a VP-30 or Cline. I had read a number of posts where people had used the Perry VP-20 (oscillator) with success (it doesn't require drilling/tapping the backplate) so I gave that a try. I knew it wasn't the right answer, but I got by for a while, constantly fiddling with tuning it correctly. You see, I mounted my tank back close to the CG in my CMP Giles 202 140. Anyway, I could set it very well with 1/4 tank, very well at 1/2 tank, and at full tank, but never all 3 at the same time. It was very frustrating and I broke my flights into 2 six minute flights on most occasions. I had all the "experts" try their hands at it, never with any success. I'm sure there are guy out there who could get it to run well, but I could not.