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Can ANYONE verify the 1974 vapor canister will work on my 72 small block? The original canister is silent when shaken, My garage smells of gasoline. Now, when the system warms up while driving, the engine misses and backfires and then COMPLETLY shuts off. Installed a ventilated gas cap with no improvement. Moved to Idaho from California 3 years ago and never had this problem before. (Thin Air?
Frustrated in Idaho.
At what elevation levels did you operate the car in CA and what is it now? Higher elevation requires a leaner setup than sea level. Generalizing, you shouldn't really see much difference unless you're changing 3000'+ and you shouldn't have your issues regardless. Going to higher elevation will cause an overly rich condition that should be visible on your spark plugs. I think you're going to have to start with a basic tune-up.
The vapor canister is a passive system that uses engine vacuum to operate. If the '74 can has three vacuum nipples, it should work fine. If only 2 nipples, I'd think you could change the vacuum tubing to match the '74 setup but am unsure what's involved. By putting the vented cap on, you've bypassed the canister so as to make it inoperable. You'll want to change back to the non-vented cap if you reactivate the vapor canister.
Do a search on the forum for replacing the charcoal and filter. You may just need to do that. There's also a liquid/vapor separator valve on the gas tank (if true to '72 design) that is supposed to keep liquid fuel from reaching the canister and saturating the charcoal.
Most corvette venders have the filter. I sourced charcoal from an aquarium supply. Worked best for me to get the charcoal very dry first by leaving it out in the sun for a day. Cracked the canister apart as gently as possible and glued it back together with cyanoacrylate.
Can I just by-pass the cannister? There is no PCV on the crate 350/355 I installed about 10 years ago.
Yep, but cap the tank nipple that runs to the separator valve on the driver's front top corner of the tank. The valves do deteriorate, so you'd want to isolate it from further fuel exposure to eliminate a potential liquid or vapor leak. Keep the vented gas cap.
For excessive fuel smells, look at the bottom of the tank to see if there is any fuel staining. If you see staining evenly distributed across the bottom edge near the center of the tank, the filler neck where it is screwed & sealed to the tank could be leaking a bit or the rubber fuel neck boot drain may be disconnected or deteriorated. (The drain hose should run from the overflow cup to the rear of the tank and down behind the passenger bumper.) If the staining seems toward the passenger side, that would lead me first to the rubber lines that feed the fuel lines to the engine. Driver's side stains would lead me to the vapor valve and lines connected to the steel line to the vapor canister.
Lastly check the rubber lines to the fuel pump at the engine.
Can you just delete the charcoal canister? Absolutely.
I lost mine years ago. And no fumes in my garage.
perhaps look elsewhere for your running issues. I seriously doubt this is causing your car to die.
Replace all rubber fuel and cannister lines on a car that old for starters. I had small amount of fuel in the cannister bought a replacement cannister for $40,...also replaced the fuel valve with a modified valve at the top of the tank on the driver side (custom tank). Replace one-way check valves if the cannister needs them, No more garage fumes.
Maybe the float levels are 1/16" too high causing fuel dripping into the carb throat...remove the filter and see if the throat is gas-damp before cranking or priming the engine.
(does the cannister "seal" itself off when the engine is off?)
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72 Vapor cannister
