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The ACV valves are exactly for what you describe is happening. You may need to pull them and check that the diaphragm is not pinholed. Just hold it up to the light, you should be able to see the pinholes if they are there. Also check that the O ring is installed properly under the ACV cover. Honda designed these valves to meet EPA guidelines for a leaner burn. They do work when everything is right.

Some have bypassed the valve's function by installing a small rubber disk in lieu of the O ring. You leave all the parts inside intact. But the action of the diaphragm is stopped by the lack of vacuum thru the O ring hole. If this is done, you may need to richen the idle mixture up a bit to compensate for the fix. This can be used indefinitely, altho most replace the valve.
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