Now that the subject of fuel tank venting has come up, I have a question, also. My coupe, a model CD serial 4169 has no vents in the wing tank caps. When I bought the coupe a couple years ago, there was no check list. So, in the process of making one I found NO VENT to check on pre-flight. I called Unvair, got a catalog and found there are two part numbers for fuel tank caps - vented and unvented. Unvented caps are for serial 4424 and up. Mine, then, should be vented, but they are not. I called an "expert" and asked how the heck air got back into the tank and he said "if it is working satisfactorily, leave it alone!". So far, that's what I have done. Works fine. But looking at the fuel diagram, it appears that the only vent is from around the cork wire in the cowl tank, thru the overflow line to the left wing tank only. How is my right wing tank being vented? Am I on borrowed time? The fuel diagrams on page 47 of the service manual show a break on fuel systems at serial 3221 and up. That doesn't explain the Univair part number break at serial 4424 and up. Anybody?? Wayne Hannah 415C/D Ser 4169, Shelton, WA
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