As a beginner with three months soloing under my belt I appreciate any assistance and suggestions. I think I'm having a fuel foaming/air in fuel problem. Background - I'm flying a WM Mach I high wing trainer powered with an Evolution Training Engine. Since getting my wings I've gone to a two bladed prop vise the three bladed that comes with the Evolution Training engine. My problem occured with both props and I seem to have the engine tuned properly and verified by club members. The engine runs fine at low and mid speeds, but when I increase it to 3/4 and full throttle, both grounded and airborn, it revs up and down, isn't consistent and air is visible in the fuel line. Additionally, the foward left and right fuse around the engine vibrates significantly. Originally, I didn't have any padding around the tank, so as advised, I pulled the tank, replaced the lines, checked the tank, reinstalled it with padding. Still zero luck. Again engine runs great at half speed! Is this a fuel foaming problem and should I replace the tank with a better quality one or is this the price of buying a $70. trainer airframe? Thanks for any help.

Nitro Dew