Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Canon Manifold

Hello Everyone,

I have a quick one for you...I am putting on a Weber DGAV and a Canon Manifold on my '78 MGB. On the bottom of the manifold there are two hose fittings. What goes on here?

Thank you in advance
B Howard

I would think this is the heater bowl for the manifold. On my 76 a hose came off the back of the head to the back side of the manifold and then from the front into the lower radiator hose. A tee at the front then had a hose to the heater. When I installed an early cast iron exhaust manifold recently I ran a hose from the lower radiator connection to the front and an exit hose with a tee -- one branch to the head the other to the heater. Some have suggested that the heater bowl is unnecessary except in the coldest temps, others find it improves emmission test results. As a caution I also found that the heater bowl did not clear the new "old" cast iron manifold and I filed down the bowl casting for clearance.
D F Sexton

Yes, the connection on the bottom is to allow you to run your heater hoses to the bottom of the intake alloing hot water to flow through the bottom making the mixture burn smoother. Prior to this additiopn to the intakes, the Webers had a bad reputation of having a "flat" spot thast you just couldn't adjust out.

Simply run the heater hose from your heater box to the back side of the intake, and then connect the heater hose from the radiator hose to the front of the intake. It will run much soomther this way. However, you can simply leave it disconnected.

Danny T

Excellent...thanks so much...
B Howard

B. Dennis has the correct approach. Your car has a water take off located at the rear of the cylinder head which went to the Z-S water choke. Run a short line to a T fitting, then connect the water output line from the heater on one arm of the T and the line to the intake manifold to the other. From the front of the intake, run the line to the lower radiator hose.

If you do as Danny suggests, you would need to make a blanking plate for the rear water port on the head. His method works for using the Weber on the pre-Z-S cars, but, for cars having the water takeoff port on the cylinder head, the direct connection is better because water will flow though the intake all the time rather than just when the heater valve is open. Les
Les Bengtson

O.K. two more question for ya...I'm almost there I promise :-).

1)Where does the line go from the canister (left side by the firewall, line runs from it to the old carb)?

2)I assume that the line that goes to the brake booster connects to the fitting in the underside of the air this correct?

Thanks again to all who have helped in my first major MG project :-)
B Howard

B. The line from the brake booster goes into the intake manifold and there should be a drilled and tapped hole for this. Use the piece off the old intake manifold to screw into the new one to provide the connection.

Line from the vapor cannister is plugged as it is not used with the Weber. Get a rubber slip on plug from the local parts store.

Line from the front tappet cover goes to the fitting on the underside of the air filter and provides your "slight source of negative vacuum" as part of the PCV system. Les
Les Bengtson

Oh...o.k. now I see...thank you so much...I actually overlooked the fitting on the manifold...

Is it possible to remove the canister or is it better to leave it in place? If it is possible to remove it, how involved is the removal? I like a clean engine bay so if it's not needed...all the better...

Thank you very much (again) :-)
B Howard

1) the line from the carbon cannister can be plumbed into the air filter -- you may have to drill a hole and buy a fitting -- mine at present is open to the atmosphere.
2)the brake booster line goes into the manifold -- the fitting from your old manifold should fit the back hole on the Cannon -- replaces the plug.
3)the front side cover can vent into the air filter

check this link for good pictures of the hose routing

Good luck,
D F Sexton

Sorry to be repetitious -- Les types faster.
Leave the cannister -- it provides the vent for the gas tank and valve conver and is good for the environment without robbing power.
D F Sexton

Excellent pics...this will help a lot (a picture is worth a thousand words) :-)
B Howard

Dennis. The hose going from the original carb to the charcoal cannister was the fuel vapor line for the carb float bowl. The Weber DGV does not have a take off that requires this line. Hence, the line is not needed (the line from the center of the charcoal cannister to the valve cover is the "output" line for the cannister). While you can, if you wish, run a line from the charcoal cannister to the air filter, I would not suggest it for two reasons.

First, not being needed, it is an extra line in the way.

Second, the PCV system is set up to provide a weak vacuum at the charcoal cannister, going through the valve cover, down the pushrod holes, through the crank case and out through the front tappet cover to the air cleaner. Not sure what effect you will have if you start sucking at both the tappet cover and the charcoal cannister. Something like trying to suck at both ends of a hose at the same time?
Les Bengtson

Be sure to hook up the coolant line to the manifold as it will help your car's driveability in the winter - a lot and in the summer too as it keeps the manifold cool.
Mike MaGee

This thread was discussed between 19/10/2004 and 21/10/2004

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.