Dont panic, remove the back plate, put a thin but unbroken line of RTV Oxygen sensor safe silicon sealent around the flange replace back plate and relocktite the screws in place. Make sure your cooling head is on staight the screws may have backed off. Relocktite them also. Remove your carb and use RTY sealent around its flange. Make sure your pipe is sealing up with two springs not just one. Air leaks will mess up all engines idle and tuning and some more than others. I do this to all my engines cause you cant trust the factory and you cant trust o-rings. I have never had a bearing leak in such a new engine and I own 14 of them. Make sure you fully warm up the engine before you tune it and start you settings off rich and work your way to lean.