The RC Valve acts "strangely" in neutral. It's only when the bike is in gear, and varying throttle openings are used (and varying rev's), that it seems to work "as it should"!
It's often normal to see the Valves "twitching" a little on idle. They will open up fully until about 1800-2000rpm in neutral, then close, then as the revs drop a little they will open again, and keep repeating this cycle. This can be a real pain when setting the idle speed too if the carbs are not set up properly!
If you can get the bike on a dyno, you should be able to see the system working properly. Alternatively, start the motor with the bike on a workstand and run the motor up through the 'box to cheeck all is well.
It is strongly advised that you roll the bike up against a wall and secure the front brake when you do this!
Andy.
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