Fuel Return on 69 Camaro

I have a 69 Camaro RS SS that I have restored to original. It has the fuel filter before the carb that has the return line. After running, it builds alot of pressure in the gas tank. When I go to remove the cap to put gas in, I have to do it slowly so gas and the pressure is relieved slowly. This surely can't be normal, why is there so much pressure. Can I just plug the return line to keep this from happening? Thank you, Chris  

The older cars had a vented gas cap. It vented to the outside of the car. I don't know if that will help your situation or not.
Try drilling a 1/16th hole in the gas cap and see if that does it. The only thing that you will notice is when your around your car you will smell gas.....
Thanks
Bob  

I have bought 2 new vented caps and put on, but maybe they are vented to let air in so it doesn't draw a vacuum. I can try drilling the hole in one of them when I get it back out for the summer. Thanks!  

please don't drill a hole in the gas cap...

it will just leak fuel all over the back of your car..

the gas caps are vented only on the suction side... so air will rush in as fuel is used up...   preventing the fuel from surging out the filler neck..

how close is your exhaust to the gas tank....

do you have an infrared thermometer.. where you can measure the gas tank temp in the bottom center before a drive.. and then after a drive... in the same spot.. below the fuel level..

just curious..   you should be able to see if you have a single line to your fuel sending unit... or a dual line version..



i am also taking that you have gone back to a transverse muffler  right in front of the gas tank..  is there a heat shield on it to prevent the infrared from the muffler from boiling the fuel in the gas tank..

or if you have mufflers under the car.. without downturns.. where the exhaust if blowing right back at the rear axle..  that may also boil the fuel...


more to come after some research..  

Some of the old muscle car gas tanks had a vent that was actually installed in the upper part of the neck when it was manufactured.It's a simple fix and what I told you is exactly what was done at the factory on muscle cars. Sometime the holes weren't big enough from the factory also.We see those problems today similar to yours because thats the way the tanks are made period.

It would go directly under the cap when the cap is sealed. (PLEASE NOT ALL GAS TANKS WHERE VENTED THAT WAY) most were vent to the outside.  If you wanted you can take a cap you have and drill and tap the smallest threaded barbed fitting in the cap and tie-wire the hose down the side of the neck and when you remove the cap to refill the tank just remove the hose first. What Wayne has said is correct if you over fill the tank and just park the car. The heat from the tarmac will make the fuel boil out.

True story when we started to really get into computers in the early 80's. We also started sealing off the fuel. Sometime the cars would run so crappy, and all we did was crack the caps a 1/4 to 1/2 turn problem solved. I was living in NJ at the time and they pressure checked the fuel system. I had guys drill a hole in one and purchase a new one for inspection. Change back and forth each year. The same thing with the EGR. If it bucked put a BB in the vacuum line to the EGR. Problem solved.

(On our Race cars now we have to vent all fuel lines out side and with a check valve in case of a rollover the fuel stays in the tank).
Thanks
Bob  

I have a new gas tank, a new dual line sending unit as you pictured and I do have a traverse mounted muffler as original. I have a Flowmaster muffler on it. I do not have any type of heat sheild between the muffler and the gas tank. I don't believe they had one originally did they? Thank you for your help.  

invest in a NON contact infrared thermometer..

most AZ stores have these hanging in the tool isle..



OEM/Non-Contact infrared thermometer  about 30 bucks..
Part Number: 25245
Point and click to determine temperature range
Temperature range: -35 to +365C / -31 to +689F
Distance to spot ratio of 8:1
Laser pointer

or this one from HF... and you might have a coupon in your printed issue.. about 40 bucks..



Non-Contact Infrared Thermometer with Laser Targeting ITEM # 96451
Temperature range: -4° F/-20° C to 968° F/520° C
Accuracy: +3° F/+2° C or 2% of reading
Distance-to-spot ratio: 8 to 1


with these you can measure the fuel temp before a test drive and after...


other later model cars have this EXACT problem...   they have various forms of heat shielding...  either a thin stainless plate to block infrared..  or some kind of thick water proof felt/rubber device that wraps the front of the tank where its exposed to the heat..

i ran across one car.. that did not have turn downs on the under car mufflers.. the hot exhaust flowing across the surface of the fuel tank was enough to boil the gas..  even with the exhaust dumping out in front of the rear end .. the heat soak in the tank was too much..  

looks like a heat shield to me... on the back of the transverse muffler from flowmaster...




they also have these..  i don't know which muffler you have...