So I heard this sucking noise......

[seabeelt]

I was making some adjustments to the carb this weekend after replacing the exhaust to downpipe gasket and went to the rear of the car to retieve a screwdriver out of my trunk tool box stash...... the car is running...... as I approach the trunk, I hear this ssssssssssssssssssssssssss type noise. So I lif the fuel filler flap...... the noise gets louder. Then I notice a small hole in the top of the tank overflow pipe right next to the fuel filler cap . I guess I never really paid any attention as I have only put gas in the car 5 or 6 times since I have owned it. The car has the usual vent line running from the front of the car attached to the intake manifold (vapors) which runs to a two way valve (broken and disconnected and bypassed in the trunk) to the seperator wit the three lines going to the tank. ( now rerouted to attach to the very uppor portion of the large green overflow hose which is attached to the aforementioned tube with the very small hole) ( new euro spec fuel tank with only one vent/overflow hose) Question ...... is the hole normal?? I dont recall seeing it on my 78 or my sons 79. To my curious mind, something does not seem quite right. Am I missing something??

[bradartigue]

Are you looking at the drain hole? They all have a drain hole near the filler.

[seabeelt]

No its not the drain hole. It almost looks like someone drilled a hole in the overflow tube.


here is another photo. the hole is at the end of the end of the stick

[RRoller123]

I wonder if maybe the charcoal canister air makeup system failed sometime in the past (maybe the 2-way valve froze? line clogged up?) and a PO just drilled a little hole in the tank intake tube as you have shown, to let the necessary makeup air in?

Pete

[seabeelt]

Pete, no charcoal canister, and the vent line set up runs to a port on the intake manifold. Not sure with suction there how the make up air is supposed to work. I think I need a diagram of an early car fuel system. My service manual only goes back to 1975.
R/

[RRoller123]

Yeah it makes sense that there is some makeup air blockage somewhere in the system. A diagram would help but unfortunately I don't have one going back that far.

[davery]

So I read this title and thought it was going to be a Michigan joke. I have been in Ohio way too long.

[aj81spider]

Here's a diagram from my early spider factory manual. A higher res version can be found on my Flickr stream. Hope it helps!



Photostream version: http://www.flickr.com/photos/60643179@N07/10098981025/

[vandor]

> the vent line set up runs to a port on the intake manifold.

Hmmm, do you think the vacuum in the manifold is sucking air through the vapor hose/pipe and through that hole??
I don't see why there would be so much air being sucked through it otherwise. It would make the mixture leaner too.

[seabeelt]

Thanks AJ. I don't have any of those parts save the piece which is in the trunk, ( and has a broken pipe and is disconnected.). Makes since now that I see the diagram of the trunk piece. There is a fresh air inlet. Since the PO connected the vapor line directly to the intake manifold, they needed a fresh air inlet somewhere, hence the hole in the filler overflow tube. Hmmmm question is.... How do I want to tackle this. Car runs OK as is and at some point I will ad the dual webers.......
R/