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Wedge TR7 fuel in carbon canister-twin carb model

johnrip

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My 1980 tr7 is running well, but the bottom carbon canister (Emissions canister), by the radiator, is filling with raw fuel. I am not sure how long this took, but what would cause this? Any ideas?
 

TR3driver

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Probably a slow leak at one of the carb float valves (assuming you have carbs). The float chambers vent through the canister when the throttle is closed.

Check your oil too, as its possible for the excess fuel to get into the engine as well. When I had the same problem on a Stag, I accidentally left the key on and it hydrolocked the motor!
 
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johnrip

johnrip

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Thanks TR3driver. So if I remove the carb vent tube, and directed it into a pan, let the the car sit, I should see fuel in the pan in the morning? What does the key have to do with it, I have a mechanical fuel pump? I have seen some fuel in the oil as well. This seems like it is helpful...thanks...John
 

TR3driver

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Fuel evaporates pretty fast when exposed to the air, and my guess is that you're getting only a little bit each time you shut the engine off. So instead of a pan, maybe try tying a Baggie to the line.
Your mechanical pump will only pump a little bit after the engine is shut off, one stroke or less depending on where the cam lobe is of course. But Stags came with electric pumps and no interlock to the engine running, so it will continue to pump as long as the key is on.
 
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johnrip

johnrip

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I dont see much while the car is running, or after it sits. I did find that 10 hours after I ran it, the rear carb bowl had fuel on the bottom of it. Not much, but there was seepage. Do you think this makes sense for a leaking float valve. Is thee some sort of bybass valve?
 
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Deleted member 8987

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Couple of other things. Sometimes the pipe back to the tank has an issue....and hot outside temperature can push petrol into the canister. But...the purge solenoid...does it work, is it connected?
 
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Deleted member 8987

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Direct TR description on TR7. I thought there was a solenoid valve, but maybe that's a TR8. You may want to pop the line from the tank off the canister and let it drip once you park.
The constant depression (vacuum source) should draw all that liquid fuel in the canister back into the inlet manifolding.


Evaporative Loss Control System
The function of this control system is to prevent fuel hydrocarbon vapours from entering the atmosphere. This is achieved by providing no direct external fuel tank breathing and venting the tank through two adsorption canisters located in the engine compartment.
To prevent the canisters flooding due to thermal expansion of any fuel in the tank, the tank filler neck is entered well down into the tank, and a pipe let into the tank at maximum fuel level vents into the filler neck to
allow for fuel expansion. A liquid vapour separator is incorporated into the fuel tank vent pipe to reduce the quantity of vapour passed to the canisters.
Any fuel vapour is purged from the canisters once the engine is running by means of a connection to a constant depression region between the air meter flaps and the throttle butterfly.
 

poolboy

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I dont see much while the car is running, or after it sits. I did find that 10 hours after I ran it, the rear carb bowl had fuel on the bottom of it. Not much, but there was seepage. Do you think this makes sense for a leaking float valve. Is thee some sort of bybass valve?
That could be a factor
The TR7 does have an Anti Run-on Valve that could be drawing an overabundance of fuel within the carburetor float chamber into the Carbon Canister.
 
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johnrip

johnrip

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So, if I follow,...My issue could be the float valve is stuck open, flooding the bowl, and the evaporative system could be drawing the excess gasoline into the canister, and likely my engine oil. If the carb issue is resolved, the evaporative system could still be operating properly? Could there be another cause of the bowl seeping gas? The evaporative system malfunction wouldn't flood the bowl...right? PS the anti run valve is connected to a small hose that it connected to the top of the intake manifold, then to the antirun valve then to the first canister.
 

poolboy

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That is pretty much the scenario I envision. I've seen it on TR6's which have the same ARV plumbing and same basic ZS carbs.
That sounds like it might be correct plumbing for the ARV.
If you follow BH19, BH21, BH16, BH3 and BH4 you'll see the basic ARV plumbing.
https://trf.zeni.net/TR6bluebook/49.php

When you turn the ignition key to OFF, killing the motor, the ARV gets power from the ignition switch. The ground on the ARV comes from the oil pressure sensor and during the few seconds that it takes for the OP to drop, the sensor provides that ground, completing the circuit that opens the ARV to the manifold depression. During that interval the plumbing is open from one of the carbs' float chambers vents, to the carbon canister, to the intake manifold.
Just to be clear, each of your carbs have 2 float chamber vents.
This one identified in red is the one for the ARV plumbing when the engine is idling. The other vent for higher speeds is the round brass lined hole on the carbs' air box mounting flange.
 
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