MGB & GT Forum

My 73 BGT runs well (thanks in large part thanks to hep from you guys!). It has the original (rebuilt) HIF-4s. Here's my question:

The large hose that typically comes out the bottom of my charcoal canister is missing, as it my anti-run on valve (which I think the hose that comes out the bottom of the charcoal canister is supposed to go to). I cannot figure out what other hose is missing (which should be attached to the other side of the anti-run on valve).

Do I need the anti-run on valve? If I don't use it, can I run a hose from the bottom of the canister to dump anything that enters the canister under the car?

Also, where should the other hose that goes into the anti-run on valve attach?

I have mine capped off and I don't get any run on.

Mine did not come with an anti-run on valve (1972) I am told.

I would replace the hose on the bottom of the canister because if you have an overflow you will have fuel draining into the engine bay instead of on the ground where it belongs.

Mark-
The center port on the top of the adsorption canister is for the purge line hose (flexible pipe) that goes to the rocker arm cover, while the port on the front of the top of the adsorption canister is for the vapor hose (flexible pipe) that attaches to a Y connection to the two vapor hoses (flexible pipes) which are attached to the overflow vents on the float bowls of the carburetors, and the port on the rear of the top of the adsorption canister is for the vapor hose (flexible pipe) that comes from the expansion chamber for the fuel tank. The port on the bottom of the adsorption canister is for the air vent line hose (flexible pipe). Note that heater hose (flexible pipe) material does not work well in these applications. In addition, avoid plastic hose (flexible pipe) as it has a tendency to harden and crack. Instead, go to a good auto parts store, such as NAPA rather than a discount parts stores, and tell them that you need an emissions-quality hose (flexible pipe). Use this material for both the hose that connects the center port of the adsorption canister to the rocker arm cover and also for the hose from the front cover of the tappet chest to the fuel induction system. This hose (flexible pipe) is also known to some vendors as “oil resistant” hose (flexible pipe) and, like fuel line hose (flexible pipe), is engineered to withstand the presence of both oil and fuel, as well as their vapors. The smaller hoses (pipes), both on the adsorption canister and the vapor separator, can be made from Original Equipment fuel line hose (flexible pipe) with no problems.

You should retain the Anti-Run-On Valve (BMC Part # 12H 4295, Moss Motors Part # 367-110) fitted on the 1973 and later North American Market models. It is mounted on an angle bracket with a square hole in it that is welded to the firewall (bulkhead) in front of the absorption canister. The Anti-Run-On Valve plugs in and is held in place with a 1/4 turn. It is a solenoid-operated low-pressure 3-way air valve. This normally vents air from the absorption canister (side hose) to atmosphere (bottom hose) at all times except when actuated for the Anti-Run-On mode momentarily after ignition switch-off. It also has a vacuum supply hose which is connected to the intake manifold. During Anti-Run-On activation, its valve closes its atmospheric vent in order to induce a vacuum inside of the absorption canister. Vacuum inside of the canister then acts through the vent lines on the carburetor float bowl(s) in order to induce such a strong vacuum above the fuel inside of the carburetor float bowls that the fuel cannot exit the fuel jets when the ignition is switched off, thus preventing the car from running on. When the ignition is turned off, the ignition switch energizes this solenoid-actuated Anti-Run-On valve in order to close it, and the oil pressure switch (BMC Part # BHA 5197, Moss Motors Part # 141-715) releases it after the engine has stopped and oil pressure has fallen. The Anti-Run-On valve is open through its bottom port to the atmosphere when the engine is running, allowing fresh air to pass through and be pulled through the adsorption canister, clearing it of the vapors that have expanded into it from both the fuel tank and the carburetor float bowls, then onward through the rocker arm cover and the tappet chest into the fuel induction system to be consumed inside of the combustion chambers.

Since the OE hoses are now ancient, replace all of them with new fuel-resistant ones. They are inexpensive and readily available at any auto parts store, and replacing them now is well worth the small effort that is involved. Just be sure that all of your hose connections are tight and well-sealed. Any leakage (or kinkage) can cause the Anti-Run-On system to malfunction.

Mark,
The ARO is not necessary, does no harm but nice to have. Vacuum take off from the intake manifold.

1973 setup;



Hoses are available on eBay from time to time.
Lower hose looks like;



I hope this helps

Bruce

---

Life's most persistent and urgent question is, "What are you doing for others?"

Thanks, guys .... all of your advised was helpful.

I spent some time this afternoon pulling my charcoal canister, putting clean charcoal in it, painting the bracket, and tidying up the back corner of my engine. Looks good.

Bookmark