On my '69 car, I have had issues with the fuel pressure since I've owned it. When I had the smaller V-8's under the hood, it wasn't such an issue, but now that the 406 is in place.... I have pressure building up in my tank. I did some research and found that there is a vent line on the forward passenger corner of the tank. I disconnected this rubber piece from the metal line coming from the tank and blew some air up the line that is supposed to vent. My buddy took a look up under the tank and said that I am missing the vent line. Now I am more confused than ever. :D What is the metal line coming from the front side of the tank (connecting to the rubber piece that shoots up into the inner 1/4 panel? Do I not have a vent tube because my car was originally equipped with a 307? Anybody dealt with this or have any answers on what I could do to keep the pressure down in the system?

Thanks! Dano:)

:thumbsup:Update: I think I have found both the root cause and the solution... The smaller v-8 cars and 250 6 cylinders all got non venting sending units. The bigger engines got 2 or 3 lines coming from the sending unit. I added a "bigger" v-8 and never knew to upgrade the sending unit. If you smell gas in the interior of the car, have a huge buildup of pressure in the gas tank, or similar problems, try looking at the forward passenger corner of the tank and see if you have 1,2, or 3 lines coming off the sending unit! Hopefully this will help some folks in the future! :beers:
Dano

I'm not familiar with 69 tanks, but here's some general info. Fuel tank vents have a check valve that only lets air in, they do NOT let pressure out. If they let pressure out, you'd fill up your garage with gasoline fumes. Pressure in the tank is completely NORMAL for any car that predates charcoal canister evaporative emissions systems (1974?). In fact, if your tank doesn't build up pressure on a hot day, it would indicate you have a leak somewhere (usually a fuel cap/filler tube problem).

Dan I never saw 3 lines but the Qjet engines got a dbl fuel line sender. The holley carbs in the Z's got single fuel lines so I wonder why your's is being fussy?

Well...all I know is that MarkLW was helping me wrench on the car a few days back and he said that the cap made a wooooosh when he removed it. I believe that this is normal to a certain extent, but when he let it sit again (in the sun) and started tinkering with the Holley4150, he saw that the vent tubes on the carb were peeing a healthy stream! I KNOW that this isn't normal. I am taking the car in for dyno tuning tomorrow am, so I'll ask the guru's what they think. They have 4 1st gen Camaros in their shop right now, and they all have bigger hp/tq than I do... I read some similar posts here on TC and saw that Click was having problems, along with a couple dozen other guys. Having too much pressure in the fuel system would sure explain the rich condition with the 327 I had in the car last year and the fact that the 406 is becoming a pita to lean out. I'll keep posting. My next plan of attack is to take the car back up to Marks in Canada and install a new tank and sending unit (which has the vent built in). Something will turn up and then I can make the proper changes...
Dano:)

Have you tried just going to a vented gas cap? I'm not sure if that is an option on a duel line sender.

On alot of the other posts I have read, guys buy a "vented cap" and turns out they are defective. I am on my 2nd one currently. I know that the one on the car is vented and working properly. I just got home from the dyno tune and the owner of the shop said that it probably wouldn't change a thing since it has no charcoal canister. It's "just the way they were" back then. The good news is that we did 4 pulls and I wound up with 400.2 ft lbs of tq and 288.3hp at the rear tires at 3800 rpm. I can live with that!:D
Once I get the new tank and sending unit in, I'll post back any changes I notice....
Dano:beers::thumbsup:

Dan -

As far as I know, there is no "vent line" on a 69 gas tank or sending unit. Some (all?) of the Q-jet cars had a pressure return line to the tank, but that's not a vent. The '69 tank is vented via the gas cap.

Al,
MarkLW was showing me in the manual where there were upwards of 3 lines coming off the sending units in '69. I don't know the rationale for it, but I saw it in the book, so it's gotta be... I am going to put on a new tank pretty quick here and add a new sending unit with 2 lines. One for the 3/8" towards the carb and one for a vent line shooting up into the inside 1/4 panel... I'll let you know how it works out.
Dano:)

My 69 has only one 3/8" line from the tank sending unit forward. My camaro was originally a small V8. When I release the cap I usually hear a whoosh. No problems. Maybe the issue is farther forward (fuel pump or carb). If you think the pressure in the tank is causing it, how is it getting by the fuel pump? Wouldn't the diaphram in the pump stop the forward flow? Maybe the fuel was just expanding in the carb causing it to pee out the vent tubes. I'm just taking stabs in the dark, but I have only heard of some return lines as one other person stated earlier. Look at Rick's website and see if they list a sending unit with a vent line for a 69.

Dan, I don't know of a vent line from the sender either, if it has 2 lines one a return and other is supply line and vent through the cap. If you think tank pressure is causing problems put a fuel pressure gage at the carb to see how high the fuel pressure is. Not sure how the fuel would come out the bowl vent tubes as they are rather larg, could it be the accelerator squiters, if so heat from the manifold can cause them to squirt and if this is the case you may need a heat sheild or a carb spacer.

Just some ideas for you.

Went up to Canada this weekend to visit MarkLW + family... We installed a brand new tank. Mark had welded a vent port + nipple on the corner of the tank. We routed some fuel line off the nipple to the trunk floor with self tappers and some rubber clamps. The last step was to drill through a bolt both length wise and across the head and installed it into the line. I filled up enough in Canada to make it across the border and then again on the US side and made it home with no more gas smell! I will have to get a heat shield for the carb in the near future, but regardless of the car having a vent line from the factory or not, it has one now and I couldn't smell any gas fumes as I did periodically before...
Dano:beers::thumbsup:

You need to put a check valve on that vent line, especially if you ever park the car inside a garage.