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MG MGB Technical - Z/S needle valve, red powder in float chamber

Hi All,
After a carb rebuild, i tried to replace the needle valve (included in the MOSS rebuild kit). The old valve is pressed in so tight, can't get it out. Do i need to drill?

Although found a large ammount of a very fine red-brown powder in the floating chamber. Is this rust from the fuel tank?
Even the spark plugs were reddish in color, did this eventually cause damage to the engine?

Thanks for inputs.
Regards,
Reto, Dubai
Reto Schlumpf

Hi,
Sorry, I might have used the wrong term, its the valve of the metering needle which i cant get out (pressed in very tight).
The hole has a slight oval shape and i assume this is one of the reasons that i can't set the idle running properly.
Reto
Reto Schlumpf

Reto - The red powdery substance in the float chamber is rust particles. You need to check you fuel tank and probably need to have it cleaned, checked for holes and then sealed against further rust. Cheers - Dave
David DuBois

Dear David,

Thank you for your input. Yes I found the tank to be very rusty inside. Strangely it looks absolutely ok from outside. I am considering buying a new tank.

Sorry to ask this again, but does anyone has changed the brass type metering needle jet. It looks to me that a hydraulic press is required...

Thank you for any inputs.

Reto
Reto Schlumpf

Do you mean the float valve or the main jet/needle in the piston? And is this HS or HIF?

The float valve body should unscrew with an appropriate socket of around 5/16" (I'm guessing here) AF. Where the float is all plastic its height is set by adding or removing washers under the float valve. If the float has a brass tang the float height is set by bending this carefully. But float height has relatively little effect on mixture unless it is way out.

The main metering needle is held in the piston with a brass screw. HS jets are held in place by the jet bearing and lock nut assembly. HIF jets by the bi-metal jet lever and adjusting screw.

The very fine powder will have no detremental effect on the engine. Some 40 years ago when I got my first SU-equipped car (a Mini) a motor mechanic said I'd never get a blockage in one of those, "You can drive a coach and horses through them". Only if a particle were large enough to wedge stop a valve fully closing and stick there for a significant length of time, and in fact a particle of that size *is* unlikely to get through the jet. I don't think the reddish colour on the plugs will be associated with the powder in the float chambers, you would have to enough flowing through there to be able to dig it out with a spoon before it had any effect.
Paul Hunt 2

Dear Paul,

According your recommendation I have ordered an infrared thermometer to pin point the problem in the cooling system (other threat).

Sorry for my poor English, i just don't know the correct term. The car is a 1980 MGB with original Z/S carb US/Japan. The ident tag shows: 951, 056, 3851.

The part which i would like to change is the 'needle jet or valve' in which the metering needle (45M) fits. This part is pressed in the aluminum body of the lower part of the carb. It is not screwed in. I will try to press it out with a friend's press. This brass 'needle valve' was a provided part in the MOSS rebuild kit and my original 'needle valve' hole has an oval shape. I suspect this is one of the main reasons for the very unstable idle running.

I could not find any reference of how to change this part in any manuals as they normally show a screwed in type...

Thank you for further inputs!
Reto
Reto Schlumpf

Hi Reto - no need to apologise for your English, it is infinitely better than my attempts at anything other than English (and maybe even my attempts at English :o)). Clarification is often needed between people who have the same first language, so no problems there.

Personally I have no experience of the Zenith, and my Haynes does show the 'needle valve' (i.e. float valve) as having a hexagonal body and screwing in to the main body of the carb. However your reference to "metering needle (45M)" confuses me as Haynes also makes reference to the main metering needles as being either 45D, 454(?) or 45H. So is 45M a different type of metering needle and potentially the incorrect one for an MGB? This is held in the bottom of the air valve piston by a grub-screw, which should be *loosened* (not removed at this stage) then the special tool inserted into the 'stem' of the air valve and its centre spindle turned anti-clockwise two or three turns to expose the needle housing assembly. Then remove the grub-screw completely and the needle and housing assembly.
Paul Hunt 2

This thread was discussed between 07/01/2007 and 11/01/2007

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