fuel issue
Thread Starter
Melting Slicks
Joined: Oct 2010
Posts: 2,276
Likes: 337
From: "ɹǝpunuʍop", Adelaide, South Australia
fuel issue
'72 stock 350, quadrajet, auto, cali car, unmolested
went for a long drive last weekend in warm weather of about 32deg c (90deg f)
as i neared home, came to a stop sign, went to boot it across the intersection, cough, cough, splutter, chuga chug (you get the picture)
manage to limp to the local pub, had a quick look, nothing out of place.
went out 3/4hr later, started straight away, drove home.
pulled carby off and gave to my mechanic during the week, nothing out of the ordinary found, (was rebuild bout year ago).
put back on today, went for a 1/2hr test drive, couldnt fault it, but when i got home i thought i'd have a look in the fuel tank,,,
well, as i undid the cap i really had to pull hard to get it off, then a whoosh of air rushing into tank.
thinking a venting issue maybe? where/what should i check?
tank cap says "sealed" on it (original). still have the canister in behind the side grill.
had a lay under the back, looking up at tank,
there is a hose going to the top of the tank on the drivers side, and one going to the top on the passengers side, pickup on bottom.
went for a long drive last weekend in warm weather of about 32deg c (90deg f)
as i neared home, came to a stop sign, went to boot it across the intersection, cough, cough, splutter, chuga chug (you get the picture)
manage to limp to the local pub, had a quick look, nothing out of place.
went out 3/4hr later, started straight away, drove home.
pulled carby off and gave to my mechanic during the week, nothing out of the ordinary found, (was rebuild bout year ago).
put back on today, went for a 1/2hr test drive, couldnt fault it, but when i got home i thought i'd have a look in the fuel tank,,,
well, as i undid the cap i really had to pull hard to get it off, then a whoosh of air rushing into tank.
thinking a venting issue maybe? where/what should i check?
tank cap says "sealed" on it (original). still have the canister in behind the side grill.
had a lay under the back, looking up at tank,
there is a hose going to the top of the tank on the drivers side, and one going to the top on the passengers side, pickup on bottom.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
Something is wrong with the fuel vapor canister, I think. Is it possible that the 'trigger' hose that runs from the carb to the vapor canister was moved from a 'ported' vacuum fitting (on the carb) to a 'manifold' fitting by mistake? That line signals the canister when to dump fuel vapors into the front baseplate fitting on the carb. And it needs to be on a 'ported' fitting so that the engine does NOT suck vapors in during idle operation....only when off-idle (cruising). Not real sure that such a change would cause the tank to have a constant vacuum on it; but it's worth a check to see.
The vapor cannister should provide the vent for the fuel tank. If the activated charcoal in that canister were plugged up with something, that could prevent the tank from venting.
The vapor cannister should provide the vent for the fuel tank. If the activated charcoal in that canister were plugged up with something, that could prevent the tank from venting.
Thread Starter
Melting Slicks
Joined: Oct 2010
Posts: 2,276
Likes: 337
From: "ɹǝpunuʍop", Adelaide, South Australia
a smaller hose, closer to drivers side, comes from the front of the carb and follows the other one down to the canister in the guard
as per AIM upc-8 b-7
what does the "separator" do that is on the canister line at the tank end?
nothing has been changed around the engine with the hoses for nearly 2 years when i removed the air pump.
this has only just showed up last weekend, hope to go on a long run 2morrow, and will see if it happens again.
Drifting
Joined: Mar 2011
Posts: 1,886
Likes: 9
The black plastic device on the upper left corner of the fuel tank is supposed to allow only gas fumes, not liquid fuel, to go to the vapor canister. The tank is vented through that line. The charcoal in the canister is supposed to minimize the smell of the fuel when the tank pressure is positive.
The hose going to the upper right hand side of the tank is the return line from the fuel pump. Excess fuel from the pump gets dumped back into the tank.
The hose going to the upper right hand side of the tank is the return line from the fuel pump. Excess fuel from the pump gets dumped back into the tank.
Last edited by gcusmano74; Nov 17, 2012 at 06:45 AM.
