ORIGINAL: Vern326

I have a new Webra Speed 50 engine. I have run about 6 to 8 tanks of fuel thru it and I have never got it to run correctly. All of the fuel lines are new. The engine has alway started easy but has poor transition from idle to high speed. It will sit and idle perfect. I can run it up to full throttle, adjust the high end mixture to rich and then back off to optimum then richen it a click or two. When i reduce to about 1/2 throttle, the engine will slow down and die. If I get it down to just above idle before it dies it will keep running. I have set, reset and reset again both the low end and high end needles. Yesterday I took the carb off and completely disassembled it, I found no dirt, O rings are soft and good, no nicks, all of the orifices are clean. Today I went out to the field, the engine started easy. I let it warm up, ran it up to full throttle, reset the high end needle and it seemed to be running pretty good so I took off, got about 40' high made a right turn, reduced to about 1/2 throttle, the engine died. I did this 4 times after making minute adjustments between flights. Another member came out to the field and he tried to adjust the high end to no avail. We tried several settings with the aircraft on the ground and never could get it to run correctly. Thinking this might be a fuel pressure problem, I was going to switch mufflers to an OS muffler but the bolt center distances are not the same. I took out the exhaust nipple from the muffler stem, filed an angle on it, thinking maybe the exhaust crossing the end of the nipple may be having a venturi effect causing a sucking action instead of pressurizing the fuel tank. I intend to try the engine tomorrow to see if this helps. Any Ideas?