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MG MGA - Carburettor problem

Has anyone experienced sudden engine cut outs or running on 2 cylinders, due to a mysterious front carburettor problem? This happens on very rare occasions..once when I had the car in the UK, a couple of times in South Australia last year, and recently in New Zealand. Each time when the car comes to a halt, all I do is tap the side of the front float chamber with a spanner, and generally the car fires up and I'm away. Accasionally I have taken the float and needle out of the chamber, and also withdrawn the piston from the carb body and given them all a clean..this seems to help for a few months, and then the problem arises again.There is no problem with dirty fuel, as all filters are clean.
The problem doesn't appear to relate to hot or cold running, as it has happened from cold starts as well, and a couple of pulls of the choke clears it.
Any thoughts please.
Gary
Australia
Gary Lock

Gary,

If removing and cleaning the piston seems to help, you may be getting dirt through the hole in the damper cap.
The SU factory prevented this by eliminating the hole in the cap and using an internal air passage.
See attachment.

Which type of SU do you have? The hole in the cap or the internal drilling?
You must have one or the other type, but not both types of air passage on the same SU.

Mick


Mick Anderson

Mick, they are standard 1 1/2's, reconditioned by Midel 4 years ago. The cap is brass, but not sure if it has a hole, as the car(s) are still in New zealand awaiting shipping back.
Gary Lock

So this has stumped everyone!
Gary Lock

Hi Gary it really does sound like the needle sticking in the valve have you replaced them at all


gordon
g c pugh

Gary, if pulling the choke clears the problem it sounds like needle might be sticking in the main jet. This would almost certainly leave wear marks on the needle. It could be compounded by additional friction between the piston and chamber. These should be polished smooth and if there is any deep scratching will need to be replaced.

Sounds like you might need to strip and rebuild the carbs before too much damage is done!
Neil McGurk

Gary,

If the problem is the front float valve sticking and the the fuel level dropping in that bowl causing it to run on two cylinders, carry out this simple test.
When the problem occurs stop the car. Turn the ignition on and tap the front bowl (you say this can cure it). The SU pump would immediately run to fill the bowl to the correct level.
If the pump responds in this way, you have your problem solved.

The other suggestion that the needle is sticking in the jet can be tested in the standard way. Use the lifting pin to lift the piston and see if it drops freely with a sharp "clunk".

Have you marked the bell housing (piston cover) and a matching mark on the SU body? This is important to ensure that the housing is always replaced in the same location.

Mick
Mick Anderson

This thread was discussed between 13/04/2008 and 14/04/2008

MG MGA index

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