lmc tank vent

[cameyer]

Ok so i have finally installed the under bed gas tank conversion from lmc in my 64 k10 but i went to fill it the other day and found i couldnt get it to fill unless i uncapped one of the extra vent lines on the tank. I am using a filler neck from an 81 c10 and it has a vent going on the the neck and i caped the other 2 vent on the tank but it wont fill unless i uncap one of them. Do i need to add a vent from one of those? if so what do i use to vent it?

[luvbowties]

Originally Posted by cameyer

Ok so i have finally installed the under bed gas tank conversion from lmc in my 64 k10 but i went to fill it the other day and found i couldnt get it to fill unless i uncapped one of the extra vent lines on the tank. I am using a filler neck from an 81 c10 and it has a vent going on the the neck and i caped the other 2 vent on the tank but it wont fill unless i uncap one of them. Do i need to add a vent from one of those? if so what do i use to vent it?

I'd run a hose vertically from a vent and install an in-line filter into the end of the hose; leave other end of the filter open to the atmosphere. Of course, secure the filter to avoid its sagging--need to keep its open end high above the tank.
Sam

[cameyer]

Thanks for the idea! Could I run it up the stake pocket in the bed or should I be worried about the vapors building up and igniting? Also is it bad to allow air to freely flow in and out should the tank still be pressurized? And should I worry about moisture getting to the gas?
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[Sharps40]

I'd mount it up inside the fenderwell. Use the bed to fender bolts as the route for the tubing by adding clamps for the filter and the tubeing. It'll be secure, high, plenty of ventilation and if you establish the open end of the filter pointing down,,,,, sort of an upside down "J" (like an upside down P-trap from under yer sink) no water will get in to the filter/down to the tank....

Modified followup.....

I believe what I had here previously was incorrect....looking at the 63 Chevy II that neck vent appears open to atmosphere....i.e. I don't think it ties back into a tank vent.

From some on line searching, those three lines on your tank should be supply, vent and return. Many of the GM tanks had some sort of antisyphon valve associated with the vent. In any event, it appears the best solution is venting the tank to a cannister as high as ya can. Evidently, the anit syphon valves are not avaialble as a repair item and unless the cannister is high, expanding fuel will run out the vent once the valve goes bad.

[Sharps40]

Bumped up, modified response.