Weber Hose Routing

Several MGB owners have asked for these photos, so here are a few more pictures of the engine in my 1978 MGB, with an added bonus. the last photo on this page explains how to route the carbon canister hoses on an MGB that has a Weber downdraft carburetor.

Vacuum hose routing for the anti run-on valve is shown too.

MGB Engine Weber Hose Routing (left side view)

This photo is larger than it needs to be so you can move it around and get a close look at some of the hose routings. I always make fairly wide curves in my hose routings to be sure they never kink in the curve. Leaving plenty of slack comprised of wide curves between the engine and chassis of the car helps to avoid putting undue strain on the hoses. None of the hoses are near the exhaust header pipes, though they appear to be in this picture.

If you didn't know this engine was supposed to have an air pump you'd never suspect it ever had one.

The engine actually runs cleaner and gets better gas mileage set up this way than it did with the original Zenith-Stromberg carb, air pump, and cat converter. I filled the air manifold ports with 7/16" bolts, cut & ground them to fit, and peened them with a center punch and small hammer to make them look like the cast iron head material. They are difficult to see even when you are looking at the engine up close and personal.

This is generally the same image I used to illustrate the hose routing

The carbon cannister system does nothing to hinder the performance of the engine. I thought it was important that it be working properly in order to purge gas fumes from the fuel system and allow the engine to breathe freely and cleanly.

Here it is boys and girls, what everybody with a weber has been asking about!

MGB Engine Weber Hose Routing, color diagram

I colorized the hoses to make them easier to trace.

1. The black hose with a pink stripe goes from the engine breather tube, wherever it may be, to the air cleaner. Your Weber kit will have the air cleaner fitting with it.
2. The red hose goes from the carbon cannister to the air cleaner. I had to make the fitting in the air cleaner for this hose to connect to. The other end goes on the top small cannister hose barb that is above the hose barb on the bottom of the cannister. It takes very little vacuum to make the purge system work and there is plenty inside the air filter.
3. The little yellow hose that is nearly hidden by the red one is the fuel tank vent line and it attaches to the other small hose barb on top of the carbon canister. The rest of the carbon cannister system, may your car have one or two canisters, hooks up exactly as original.
4. The silver-gray hose goes from the rocker arm cover to the large center hose barb of the cannister. With the original rocker arm cover you just hook up the hose, but with an aftermarket cover like this one there is one extra step to take. Aftermarket covers usually have an wide open breather pipe as this one did. In my case, I got a bullet type, (a cup type will do), freeze plug the same size as the pipe, drilled a 3/32" hole in the center, and inserted it into the hose. This is a very simple way to restrict the volume of air drawn through the carbon cannister to the proper ratio.
5. The white hose goes from the anti run-on valve to a port on the intake manifold. Since the anti run-on valve is closed and no vacuum is drawn through this line while the ignition switch is turned on it makes no difference where on the manifold the line is connected as long as it is below the carburetor.
6. The black hose with the yellow stripe is the power brake booster hose and goes into the front branch of the intake manifold. In the third photo you can see that there is an extra port that has been plugged right near the booster hose connection. That plug came with the weber kit.
7. The vacuum advance hose, which is pretty much hidden in all these photos, attaches to a vacuum port near the bottom of the carburetor on the side next to the rocker cover.