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OS 91 surpass making a strange popping sound.

Old 08-28-2015, 08:06 PM
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twinster2
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Default OS 91 surpass making a strange popping sound.

This may sound weird, but I have a new but old OS 91-fs Surpass engine on my Topflite AT-6 that makes a popping sound from the exhaust as it flies past. You can not hear it as it approaches, but once it flies past it is very audible. The engine has about 2 hours on it and has made this noise from the beginning. Maybe popping is the wrong word, it could actually be missing. Anyway, I have tried different plugs and fuels with not change. Could this be a valve clearance or timing issue?
Old 08-31-2015, 06:26 AM
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If the engine is running well, we'd ignore random noises. Especially if the engine's at less than full throttle. You may be hearing the occasional misfire when at reduced throttle settings that have the sound amplified a bit by the exhaust system.

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