OK,,with engine at idle the carb throttle plates are closed so the cyl,s are still trying to take in air but throttle is closed thus it is creating a high vacum in the intake(((18 inches)))when you increase engine speed you have to push foot pedal it opens carb throttle allowing more air into the intake thus the high vacum falls because throttle is opened allowing air to flow freeley thru carb and intake so your vacum is down so the wipers slow or stop until you close throttle to allow vacum to increase,,so under full throttle you have very little vacum and high air flow,,at idle you have high vacum in intake and very little air flow...now I need a nap!!!!doc
