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Old 06-19-2009, 10:20 PM
J.J. LASALLE J.J. LASALLE is offline
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Locating Methods For Air Leaks In Mechanical Fuel Pump Fuel Lines

I Recently Rebuilt The A-b Combination Diaphragm Fuel Pump For My 1937 Cadillac Lasalle, Along With The Carter Carb. I Also Had The Fuel Tank Refurbished By A Tank Re-nu Facility. The Car Runs Exceptionally Well Until I Lose Prime At 40 M.p.h. On A Busy 4-lane Inter City Highway. (not A Good Thing)

I Recently Noticed, While Working On This Fuel Problem At My Home, That The Glass Fuel Bowl Started To Boil With Air Bubbles After The Car Was At Idle For 5-10 Minutes. I Know That These Air Bubbles Indicate A For Sure Air Leak, And I Assume That The Air Leak Would Have To Be On The Inlet Side Of The Fuel Pump, But I Cannot Seem To Find The Leak. There Seems To Be Only Four, (4), Places For The Leak To Occur, Unless I Am Mistaken. It Is Quite Possible That I Am Mistaken Since I Most Often Am.

(1) Fuel Line Fitting At Tank Attachment

(2) Fuel Line Fitting At The Reduction Of 3/8 To 1/4 Line

(3) 1/4 Line Fitting Into Inlet Of Fuel Pump

(4) Gasket At Glass Bowl

I Have Already Stripped The Threads Once, Since Repaired, Fuel Line Into The Carb. Trying To Stop Any And All Air Leaks, From Over Tightening The Fittings.

Any Suggestions As To An Easy Way To Locate And Remedy My Nemesis, Mr. Air Leak.


J.j. Lasalle
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