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.

To make a very long story not quite so long, I read Lou55's reply above (I read it from many people many times) and decided to give it a try. I plugged one of the two exhaust outlets with a piece of dowel. The first thing I did was bypass the VP-20 and put all the settings back to default per the manual...2.5 turns out on both the high and low needles. The engine fired right up (1/4 tank of fuel) after a generous prime, but ran extremly rich as I gave it throttle. It would idle nicely (glow plug removed), but bog way down with any throttle. I leaned it to peak and backed off about 300 RPMs. This worked out to exactly 1 turn out from closed on the high needle. I ended up closing the low needed 1/4 turn more (2 1/4 from closed) for smooth transition.

This ended up giving me 8500 RPM rich for flight. With the VP-20, I was running at 8800, so I lost 300 RPM. I realized that many of you are getting a lot more than the 8800 I was getting, so it leads me to believe I had it tuned wrong. But, it flew great with loads of power to spare (with the pump). It should fly just fine losing the little power I lost, I figured. One time I let it idle for 2 minutes exactly then jammed on the throttle. There was a very slight sputter before picking up to full RPM. There is no hesitation idling for 90 seconds or less. I repeated this with 1/2 tank and full tank and was able to maintain the same idle RPM of 1850. I did not have to adjust the high or low needle to achieve excellent throttle response from idle to any throttle setting.

I flew the plane to put this all to the test. After two tanks, I had tremendous performance from full tank to about 1/4 tank. I landed after about 12 minutes and each time I had about 1/4 of my 14 oz tank remaining. I did not fly much full throttle, but lots of 1/2 - 3/4 throtle. I could not be happier.

The bottom line is, I did not have what it took to get this engine to run well with the VP-20. I did not want to mess with drilling the backplate for the VP-30. I was not having fun with my plane/engine. I couldn't take it anymore. I refused to spend the countless months that some people had spent struggling. I went against all instinct to get this problem resolved "correctly" and went with the "quick fix" of plugging an exhaust outlet and it gave me the desired satisfaction. You can call me naive, lazy, stupid, or whatever, but it works now, I'm happy, and I'm flying.

My setup (pump the only thing changed):

CMP Giles 202 140 with clunk about 12" from carb
APC 18x6W
Omega 10%
OS #8 glow plug
medium fuel tubing (I know, large is better)
Warner Robins, GA, about 500' (?) ASL

Giddy Up! (Yes, I'm a HUGE Seinfeld fan, but I'm not Jewish, not that there's anything wrong with that :-)