Vacuum is ported not manifold. Not sure on kick down. My guess is some one changes something over the years. I dont like the idea of a fast flush on an engine. IF the engine is sludged badly then you will loosen it enough to block the screen and blow it up. I like starting with fresh oil and 500 miles before changing it I add one quart of transmission fluid to crankcase and drive it easy. Not towing or racing. The trans fluid is High detergent and will slowly clean engine just as it slowly got sludged up. I have done this on all my old cars and never had a problem and have it has done wonders for oil consumption also.

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1964 Galaxie 428
1966 Mustang 302
1967 Cougar 390
1968 F250 Camper Special 390