pgeders

Have a '73 that is got me a little puzzled. When I filled up with gas, up to the bottom of the tube that extends down into the tank, last week I noticed a 3 foot diameter puddle of raw gasoline coming from the vapor canister behind the left front wheel. I was sitting on fairly level ground...maybe a slight left side lower for water drainage on the concrete pad at the station.

Got out the assembly manual and looked at the system. Seems there is a vapor separator, part number 7028035 on the left top side of the fuel tank with rubber hoses from the tank to the separator then to a steel line that goes along the frame and into the vapor canister. I looked at the installed vapor separator and it is intact, no cracks, etc.

Was wondering if the vapor separator, which I believe has a foating type check valve may be malfunctioning. Also, since the parts are all original, the vapor canister purge valve could also be ineffective. Anyone seen this problem and what resolution did you use?

My thoughts are to replace the vapor canister assembly (still available through GM) and take off the vapor separator and see if it is functioning correctly, but don't know how to check its functionality. Anybody know how?

Could this also be causing poor mileage, by sucking some raw gas off of the tank through the vapor canister and into the manifold? I have a 350 bored over .030 with a 268H cam. I am getting about 9 to 10 MPG babying it. I would think it should get around 15 MPG!

Any help would be appreciated!

jackmoore

can't we just eliminate all that mess? I'm a functional sort of guy over a purist. seems we could put it all back on later?

87bob

News flash! I had the same thing happen while at Vettes on the Rockies a couple of years back. The hose from the tank line to the vapor canister cracked in a spot that I could not see it from the top or the bottom. I had to pull the left splash guard and then I could get access to the lines. Those rubber lines are in one of the worst places in the world. You can't see them and don't know they are there. The lines get old brittle and crack if someone is running side pipes the fuel will leak right on top of the hot header and poof! Toasted Vette.

stingraydriver74

i'm going thru a simila ordeal on my 74, i recently replaced my gas tank, and while we were installing it we broke the seperator. we bought a new one and i attempted to install it with no luck, can't get to the darn thing without droppin the tank which is a hellish job. so i reached up there and plugged the hose coming out the side with a bolt, it did stop the gas from sloshing out but i don't know if there will be any side effects of doing that, i only test drove it once. if anyone has learned something the hard way let me know before i blow myself up

Brad

Patrick73

There have been several good previous threads discussing the "gas vapor separator" which is the correct GM part name for the valve on the gas tank. It is now a discontinued part. Member "Carl a" has posted the best photos and discussions on this subject. So have members Joe73vette and Gusto14. You can search their postings to locate in depth discussions on this topic.

Only 70 to 74 models use the part; it is part No. 7028035 and is in GM catalog Group 3.120

Carl a has removed and repaired the part using epoxy. The part can be removed without dropping the tank. A leaking valve separator is also a common source of raw fuel smell in the garage.

pgeders

Replaced the vapor separator 7028035 and vapor cannister and the problem of leaking fuel out the vapor cannister and no gas smell in the garage is gone. Took about 25 minutes to replace the vapor cannister and related hoses with new ones. Old vapor cannister was the original unit and heavy when I removed it. Probably because it was 32+ years old and still had some gas and probably dirt built up and/or trapped in it.

The vapor separator took about 45 minutes to replace...small 1/4" drive air wrench and right tools helped alot. Jacked up left rear suspension and worked around the muffler. Replaced the related hoses on the vapor separator too. The replacement separator ball float seemed to be a lot freeer than the old one I took out. I cleaned the old one out with MEK after testing the plastic to make sure it was impervious to it. Now I have a back up that must have been just gummed up a little and not shutting off the line to the vapor cannister. Separator had no cracks and held both positive and negative pressure (about 5 psi) without leaking.

So the long and the short of it is...replace with new/proper components and we're back to normal...the way it was designed to work!