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Triumph Repair/73 Triumph tr6


QUESTION: I recently started to work on my dads 73 Triumph tr6 after it had been sitting for a good number of years. He kept it in good shape and after replacing the fluids I was able to get it started, however there was gas pouring out of the bottom of the anti run on valve. I'm not quite sure how to fix this or even how the evaporative loss system works on this vehicle and haven't been able to find anything online about it thus far.

ANSWER: Hi Nick,

The fuel can be coming from the carburetor and/or the fuel tank.

The anti run-on valve is a solenoid that allows vacuum to be transmitted from the the intake manifold to the charcoal canister and on to the float chamber by way of the anti run-on valve to cut off fuel available to the carb jet when the ignition is turned off. However the charcoal canister is connected to the venting of the fuel tank and the carb float chamber vent so if either is over flowing with fuel it fills the charcoal canister and goes into the anti run-on valve.

Here is what to do to diagnose it. Remove the hose from the fuel tank at the top of the charcoal canister and shake it to see if there are any droplets of fuel in the hose. Then open the fuel tank filler cap and blow air into the hose and note that it exits the filler neck as a hiss not a bubbling sound. Also confirm that the tank is not over filled.

Next remove the vent hose from the carburetor that goes to the canister. Shake that hose too to see if there are any fuel droplets of fuel in it. If not replace that hose on to the carburetor and remove that hose from the canister and shake it for fuel droplets. Now place that hose down toward the ground (outside not in your garage) and start the engine and let it run for a while watching that hose to be sure no fuel comes out of the hose. If it does the float is stuck in the carburetor. (common when a car is stored for some time)

Either way your charcoal canister is destroyed since it is saturated with fuel no matter which the fuel came from. BLM use to sell the charcoal separately for a while a long time ago but I have not seen it available in years but you might check with some of the Triumph parts suppliers and MG parts suppliers.

Let me know,


---------- FOLLOW-UP ----------

QUESTION: Hi Howard,

First let me say thanks for the quick reply.

From your advice above i have determined that the excess fuel was coming from the carburetor, however it only comes out after the engine is turned off. I have already cleaned the upper part of the carb, replacing the diaphragm in the process. I'm assuming my next step is to tear the float chamber down and clean that out?

Thanks again,

Yes, You are on the right track. Check the float for saturation and the float setting after you replace the most likely cause which is the needle and seat need to be replaced. Don't forget to replace the charcoal canister as it is destroyed one it has fuel in it.


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Howard M. Fitzcharles III


Triumph TR-4 up & Spitfire, and Engine theory


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

Associate member SAE EAA member

Import Car magazine

ASE Master Auto with L-1 certification up to 2000

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