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MG MGB Technical - High idle 73B weber DGV

Hi everyone-
I replaced the head gasket (looking for a washer that might have went down the intake but was never found) and also replaced the air filter on the DGV at the same time (and also a new alternator). It started up but is running at about 2100-2200. The choke is disengaging. The idle screw is not even in enough to touch the throttle stop lever. Moving the mixture screw from all the way in to 2.5 turns out does not seem to change anything.
Any ideas?

Looking at the lower part of this picture, http://www.carburetion.com/Weber/idle_a1.gif, the idle screw is the one with the spring and the mixture is the one above it right?

Thanks
Jason
Jason Smith

Here is the pictue


Jason Smith

check for air leaks. check your primary throtle plate to be sure it's centered RIC
RIC LLOYD

Jason. The first thing to do is to remove the carb and make sure that the primary and secondary throttle plates are fully closed when the idle speed adjustment screw is not making contact with throttle mechanism. If both plates are not fully closed, you cannot adjust the idle speed properly. Re-install the carb on the intake manifold. Do not hook up the throttle cable. Set the idle mixture screw at two turns from fully in.

See if the car will start and if it is still idling at a higher than normal rpm. I have seen throttle cables which were too tight when attached to the carb, not allowing the throttle to fully close. If the car does not start, use the idle adjustment screw to open the throttle a little, or recruit an assistant to operate the ignition switch and you operate the throttle manually. If the engine will start and idle properly, your cable was a little too tight and was holding the throttle open.

If the engine starts and still has a high idle, it is time to check for air leaks around the base of the carb and where the manifold attaches to the cylinder head. Either a spray bottle of carb cleaner or an unlit propane torch is used for this experiment. The engine will run better when the air leak is momentarily plugged by the carb cleaner or when the propane is being drawn into the leak. If there is an air leak, correct the problem.

If none of these tests find the problem, post again with the results of the tests and we can go to the more advanced problem areas.

One thing to note is that some of the carb to intake manifold gaskets are directional. They are smaller on the side where the primary barrel goes and larger on the side where the secondary barrel goes. I have seen them installed backwards without a high idle problem. But, your gasket might, if installed correctly, catch the secondary throttle plate and not allow it to close fully. All worth checking out.

Les

Les Bengtson

Whilst an air leak *will* cause a high idle for a given throttle opening when compared to no air leak, but air leaks on their own won't cause a high idle, the engine needs fuel to be coming past the butterfly as well as air in through any leak in order to run. I know nowt about Webers but the idle screw *should* be capable of fully closing the butterfly in SUs at least, and hence shutting of all fuel. Where this problem happens in SUs it is *always* something to do with the butterfly not fully closing, or fuel being otherwise able to get through it or round it.
Paul Hunt 2

It turns out the correct screw was on the corner of the carb and not the one in the picture. Also, the cable was also too tight.

Thanks alot
Jason
Jason Smith

Or is that screw on the corner the mixture?
.... It is running very smothly at about 900 right now
Jason Smith

This thread was discussed between 30/06/2007 and 01/07/2007

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