Larry - if the rotor and cap are new - quite possibly the coil is shorting out from the moisture. It cannot be a sparkplug wire as all cylinders are affected. Meter the wire from the coil to the cap as a precaution and run the motor in a dark spot with the hood up looking for stray HV when it is damp out and acting up. See if it will act up by increasing the throttle from under the hood and look for stray HV when it occurs. I would hedge towards the coil however. It may meter good on the primary, but could be jumping the HV internally because of moisture. Check the coil for any cracks in the coating that could allow moisture in. Let us know when you find it.