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This thread has generated much interest, and here's my convoluted addition, which to me is a bit of a puzzler. I have a fairly new s/s fuel tank installed by the PO but it has no opening for the fuel guage sending unit, just a small 5/8 inch opening with a bolt that the PO used with a dipstick to check fuel levels. Being a perfectionist, I wanted to have the fuel guage work properly. I wasn't prepared to remove the tank (meant dismantling half the rear end of my boat!) and have a new port cut into it, so I decided to install a small secondary tank with a syphon connection and containing a new sending unit. The syphon is a copper tube going to the bottom of the primary tank and a clear poly gas line to the secondary tank which is also vented (I wanted to use clear poly initially to check it all works). It all works fine but I noticed that tiny air bubbles could be seen coming from the primary tank and very slowly filling the syphon line with air over a period of 4 or 5 days, such that the syphon no longer works. I've checked for leaks and found none, so assumed this was dissolved air in the gas coming free (I'm no hydraulics expert!). I use a bulb to prime the syphon every time I use the boat. My question is: if this air is evolving in my syphon line, it must also be slowly filling the main line to the fuel filter as well and I wonder if sometimes the electric fuel pump cavitates until the air is eventually sucked through (main tank is above the engine and only about 2 to 3 feet from the carb), because sometimes the engine starts very rough when started and runs rough for about 10 minutes then runs fine. Am I way off course or is this possible?
Bob Griffin
C&C Corvette 'Saga'
Bath, Ontario.
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