bubbagates,

Not sure what the apology was for, if I sounded harsh, I hadn't meant to. BTW, all my gas engines have the line running into the fuselage. I don't think it is a clunk problem because of what I experience with the sudden, harsh, up or down movement. The engine hasn't had a chance to run low on fuel because it happens both upright and inverted. I'm going to switch back to Zenoah's straight velocity stack that came with the engine, replacing the beveled one, and see what happens. If that doesn't solve it, I'll replace the clunk as you described.

Chuck