Drilling gas cap

[Ian]

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.

[Ian]

Anyone?

[monte70car]

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

[kc8oye]

drill a 1/8" hole right thru the center of the cap.

 

but it would be better if you could vent the tank so you don't spill fuel out when you launch it.

[wallaby]

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.

[Winston Wolf]

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.

[Ian]

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.

[kc8oye]

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

[SS Haze]

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.

 

Mike

[Ian]

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

[kc8oye]

are the vented caps a one way valve? they will let air in, but not pressure out?

 

[Ian]

Yep that is how they work

[kc8oye]

i.c. that makes more sense then everybody having issues with them not venting correctly!!!