30 percent nitro is too much nitro for this engine. I believe you mentioned hearing metal noises when flying - that's pre-ignition from running too much nitro and running too lean. If this engine doesn't run well using 10 to 15% (with a 12x7 prop), then you have cooked the engine. One of the worst combinations you can run into is runnning a high nitro with too lean a mixture and a hot plug. Certain death for an engine.