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MG MGB Technical - Charcoal Cannister Hoses

I have installed SU carbs in my 77 MGB and am questioning where I need to hook the hoses that exit the top of the cannister. I know that one hose goes to the tube that is on top of the valve cover but am not sure where the other will go. Can I run the hose to a vaccumm nipple on the intake?
J Fleshman

One hose from the top of the canister goes to the fuel tank breather, one to the carb overlow/vent ports (via a splitter for dual carbs), and one to the rocker cover. Apart from the splitter for the dual carbs this is exactly the same as for the single Stromberg carb.

The bottom of the canister should go to the larger port at the top of the anti-runon valve, the smaller port at the top of the anti-runon valve goes to the inlet manifold, and the large port at the bottom of the valve is open to atmosphere (or may go to a 2nd canister before going to atmosphere), and again this is exactly the same as for the Stromberg.

What is more important is what have you done about crankcase ventilation? Do the SUs have the breather ports angled up and across the rocker cover? If so these also need to be connected via a splitter to the port on the front tappet chest cover, where the Stromberg would have been connected. If the carbs don't have these ports then you should fit a PCV valve to the inlet manifold, connected to the front tappet chest cover.

What about the gulp and EGR valves?
PaulH Solihull

Paul,does anyone sell gulp valves anymore?
rich osterhout

Paul,

My SU's do have the breather ports you describe and I have connected them via a splitter to the port coming off of the front tappet chest cover. Am I to understand that I should also put a splitter into the line so that I can attach the hose from the canister? Could I route the hose from the canister to a port on the intake manifold?
J Fleshman

The hose going from the tappet chest to the carbs is one system. It provides the slight negative vacuum necessary for the PCV system to operate correctly.

The connection from the two carb bowl's overflow vents needs a separate line, with a Y connection in it, then going to one of the smaller nipples on the charcoal canister. Thus, the petrol fumes from the overflow vents are drawn into the charcoal canister, just as the fumes from the fuel tank go into the charcoal canister. The canister has a larger central nipple which is connected to the rocker arm cover which provides the air source for the PCV system input.

You do not want to mix the two systems as it would effectively defeat the purpose of the PCV system.

Les
Les Bengtson

Rich-
Moss Motors sells Gulp Valves (Part# 366-010) for $99.95.

J-
Be warned that heater hose material does not work well in these applications. In addition, avoid plastic hose 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 for 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 is also known to some vendors as “oil resistant” hose and, like fuel line hose, is engineered to withstand the presence of both oil and fuel, as well as their vapors. A word of warning about the type of clamps used to secure the fuel hoses Over time, the rubber of the fuel hoses will suffer distortion under the clamp and thus reduces the pressure between fuel hose and the mounting tube. Hoses that have been secured with worm-type threaded type clamps will tend to weep, whereas fuel hoses that are secured with clamps of the “constant pressure” spring clip type do not suffer from this problem.
Stephen Strange

I don't know if anyone sells gulp valves anymore, but if one is installed presumably it has to be connected up properly. When the gulp valve is faulty the symptom is usually backfiring in the exhaust on the overrun.

As Les says there are several separate circuits and you cannot combine most of them. The canister goes to the tank vent, the carb vent/overflows using a splitter for twin carbs, and the rocker cover. Whilst you *could* potentially combine these three there is no point as there are three ports on the canister. The small port on the anti-runon valve goes to the inlet manifold, and the carb breather ports go to the front tappet chest cover via another splitter. You cannot combine any of the first three with these latter two or you will get all sorts of problems, from no crankcase ventilation to it preventing the engine from running at all. If you don't have an anti-runon valve then the unused port on the inlet manifold for that must be sealed, as must any other unused ports on the inlet manifold.
PaulH Solihull

Neither can you combine the latter two, by the way.
PaulH Solihull

This thread was discussed between 19/08/2010 and 20/08/2010

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