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MG MGB Technical - Leaky Weber

Hi,

My Weber carb is causing me some problems at the moment! About 2 months ago it started leaking where it connects to the inlet manifold. I took it all apart and saw that the misab plates were all perished and broken. I ordered some new misab plates and fitted them, thinking I had solved the problem.

My car was parked up the other day and I could hear the drops of fuel evaporating as they dropped onto the exhaust manifold. I put my hand under the carb and it is leaking again!!

Anyone else had this problem and know hot to fix it?

Cheers Joe
Joseph Phillips

Joe. What model Weber do you have? It would be useful to know. The term "misab plate" is not one I recognise. Les
Les Bengtson

I've had a Weber downdraft on my MGB for over 10 years. The only maintenance it has ever needed was to clean the air filter (a K&N), replace a worn cotter pin on the accelerator linkage, and to occasionally slightly tighten the screws that compress the washers on the carb body. If by "misab plates" you mean the gasket between the body and the inlet manifold, the key here is not to overtighten. Perhaps the inlet manifold is bent (or the carb body)due to over-tightening. Before resurfacing either the inlet manifold or the carb face, I would try a thicker gasket. You should be able to make a new gasket with neoprene/cork/paper gasket sheets from any auto supply store. Use the old one as a guide (trace it), and cut out a gasket with an Exacto knife. The key is not to overtighten; but you will likely need to slightly retighten the screws after the car has gotten warmed up and cooled down a few times.

Be careful with fuel leaks-- I went to a Weber due to a leaky single carb setup.

Ira
Ira Spector

Sorry guys, its a 45 DCOE (sidedraft). 'Misab plate' is the gasket between the carb and the inlet manifold, just a small rubber ring on a metal plate.

Ira,

I made sure I didn't overtighten the carb, I have pinched it up since and it has made no difference.

Joe
Joseph Phillips

Joe. I thought as much since, like Ira, I have had no such problems with my DGV series carbs. I have no experience with the DCOE series. Daniel Wong, who has posted recently, does have some experience with the DCOE and it might be worth e-mailing him off line. I do not know if he reads the boards every day.

Since you understand that I know nothing, might I suggest that the first thing to do is to find where the gas/petrol is coming from? There would seem to be two possible sources. First, the needle valve is not shutting off properly and you are running very rich. Second, fuel is condensing out of the fuel/air mixture as it if flowing from the carb venturi to the intake manifold. You might want to check the functioning of the needle valve and the pressure of your fuel pump.

The next area to inspect is to determine why the fuel is leaking from the carbs when the car is stopped. I would expect that, for fuel to leak out, air must be leaking in when the engine is running. Spraying WD-40, carb cleaner, etc. around the gasket areas is the standard test for air leaks. There is a discussion of this technique on the thread about the Weber 38/38 downdraft currently running.

Sorry that I can be of no direct help. Les
Les Bengtson

OK, here's my shot...

For a DCOE...

Get an inspection mirror and check underneath the
carb and look for the fuel chamber bottom cover.
It's a small, square, cast aluminum item with a screw on each corner. Sometimes the screws will
work loose, or the gasket-screen will go south
- and then fuel will dribble out of there, and travel
along the carb flange until it drips off and wets the
center branch of the exhaust manifold. (not good)

Put a small pan under the carb to catch the fuel as
you remove the cover to inspect the gasket-screen.
You should do this occasionally, anyway, as fine
rust and silt often accumulates at the bottom of the
fuel chamber and can cause all sorts of errant
problemswith mixture.

Each of the cover screws should have a split-type lock washer underneath each head to prevent them from backing off. Applying a very small dab
of Locktite (temporary version), or similar, to the threads of each screw adds insurance against them from backing off. Snug the screws home
- but no not overtighten as you may squash the
gasket or distort the cover.

---------

On very rare occasions fuel might leak from a faulty
choke circuit mechanism (- not to be confused with
the throttle bore "choke" sleeves). I'm talking about
the cold starting choke that is controlled by cable.
The cover for this is the squarish metal plate that
is between the throttle bores, inset in the carb
mount flange. You'll have to remove the carb
from the manifold to see and access it. As I said, this happens rarely...and my bet lays somewhere
on the fuel chamber bottom cover.

You can get the gaskets and parts for these areas
either individually or from a rebuild kit from your
local trusty Weber carb supplier.
Daniel Wong

Thanks guys. I will have a good look at it this weekend.

Joe
Joseph Phillips

Adding to what has been said, you seem feel that replacing the perished Misab plates cured the leak for a while. If so, this implys that the fuel is running down from the inside the throats of the carb, where it msut be pooling (and perishing the misabs?). If so, the float/needle valve and maybe fuel pressure should be looked at to make sure the fuel supply is off when the float chamber is full. How's the car running at idle? How's the fuel consumption been?
Steve Postins

This thread was discussed between 07/01/2004 and 08/01/2004

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