I have a 30cc homelite that I converted w/ C/H ignition, it ran well for a while 9000 w/ 17x6 apc, but now it sputters at high rpm, or rather it runs dies out like like it looses spark then comes back but it does this quickly. I have cleaned the carb"walbro 167", and have torn the engine down. I do not see any signs of leaning or over heating. Could it be the plug or ignition?