Ian Posted August 18, 2010 Share Posted August 18, 2010 So here is the deal, I went with a 70 non vented tank and a 70 vented cap when I put the new one in last year. Have not driven the car much. I remember Steve (Monteman1971) said he drilled a small hole in his, how and where? It is building pressure in the tank with the high pressure fuel injection return style pump. So much that when I stopped to get gas the other day you could see it collapse when I took off the cap. Quote Link to comment Share on other sites More sharing options...
Ian Posted August 24, 2010 Author Share Posted August 24, 2010 Anyone? Quote Link to comment Share on other sites More sharing options...
monte70car Posted August 24, 2010 Share Posted August 24, 2010 Sorry Ian I cant help I know when we switched the Nomad over to the tpi setup dad just teed into the over flow tube for the return line and he dont have a issue other then the wrong chip Quote Link to comment Share on other sites More sharing options...
kc8oye Posted August 25, 2010 Share Posted August 25, 2010 drill a 1/8" hole right thru the center of the cap. Â but it would be better if you could vent the tank so you don't spill fuel out when you launch it. Quote Link to comment Share on other sites More sharing options...
wallaby Posted August 25, 2010 Share Posted August 25, 2010 1/8? Boy that sounds giant to me. I'd guess .030 would be plenty. The fuel in the tank isn't going to expand so fast that you'd need anything big. I think the vented caps have a one-way valve to let air IN, but not out...but I'm not 100% sure on that. Come to think of it, I think my old lawn mower has a filler cap with a tiny hole in the center...it's so small you'd hardly notice it. Start tiny and only enlarge it if needed. Quote Link to comment Share on other sites More sharing options...
Winston Wolf Posted August 25, 2010 Share Posted August 25, 2010 I have a 1/16th" hole drilled at the top side of the cap. I did have issues with venting before that. Too big of a hole and it will leak under heavy acceleration. Quote Link to comment Share on other sites More sharing options...
Ian Posted August 26, 2010 Author Share Posted August 26, 2010 The center of the cap is the rivet that holds the handle on. I was afraid to drill there and the handle fall off or start turning... I was thinking towards the top would work.. The center is also where the inward venting is. Quote Link to comment Share on other sites More sharing options...
kc8oye Posted August 27, 2010 Share Posted August 27, 2010 he's having pressure issues from his EFI system.. not because of the fuel getting warm and expanding.. that's why I suggested 1/8 Quote Link to comment Share on other sites More sharing options...
SS Haze Posted August 28, 2010 Share Posted August 28, 2010 My 70 has always had problems with tank pressure. If I take it out on a hot day, I have to make sure that I 'vent' it by taking off the cap each time I shut it down. I can't fill the tank because that will actually cause gas to flow out of the filler. A small hole sounds like a great fix. Â Mike Quote Link to comment Share on other sites More sharing options...
Ian Posted August 28, 2010 Author Share Posted August 28, 2010 I am going to try it the next time I get a chance to work on it. Been working 2 jobs the last couple weeks Quote Link to comment Share on other sites More sharing options...
kc8oye Posted August 29, 2010 Share Posted August 29, 2010 are the vented caps a one way valve? they will let air in, but not pressure out? Â Quote Link to comment Share on other sites More sharing options...
Ian Posted August 29, 2010 Author Share Posted August 29, 2010 Yep that is how they work Quote Link to comment Share on other sites More sharing options...
kc8oye Posted August 30, 2010 Share Posted August 30, 2010 i.c. that makes more sense then everybody having issues with them not venting correctly!!! Quote Link to comment Share on other sites More sharing options...
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