Hello ,
I have an old 91 speed regular ring webra that was new when I bought it but no box or instructions. It was not drilled for muffler so I drilled and tapped it and installed a bisson Pitts style Webra 120 muffler. Before that I ran it on the bench for break in . Ran great , idled /transition to full throttle good. Mounted it on plane with muffler and it runs fine till nose is pointed skyward .... Instant die. I have a pressure line from muffler to tank vent. Carb has two needles , high speed needle on right facing motor is springy kind , low speed on left is part of rotating barrel throttle arm assy.
Was wondering if perry pump would help, also backplate has no boss for drilling and tapping for crankcase pressure.
Help! Thanks!