After some carb work/rebuild to fix some problems it started working great. All running good. Then suddenly after  running about an hour it started running rough and only getting to 4900 rpm at full throttle. Cable getting the throttle valve open equally. Upon further investigation with air filters off it turns out that as the throttle is increased, the piston lifting the needle jet up was not going up on one carb. Lifting it manually allowed the engine to go to full throttle. It appears that the carb piston that is not going up as it should is slightly heavier. Any idea what would cause this piston/needle jet not to lift? Any ideas/experience would be appreciated.




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