MG Car Repair: carb. problem, stromberg carburetor, zenith stromberg

Question
QUESTION: Hi Howard

Have a 1976 mg midget, been having carb problems for a few month's, it will idle perfect but when I mash the gas the RPM's will not change at all, been told need to rebuild carb, it has the carb that came out on it single, zenith -stromberg, most folks are telling me not to rebuild, but to get rid of this carb because they have always caused problem and to get a different one,,,, what do you recommend ? If I need to change what kind do you recommend and were could I buy one ?

Thanks

ANSWER: Hi Steve,

The Stromberg carburetor is good and it don't take much to rebuild one.

I have to question it not changing any RPM when opening the throttle. Did you check to see if the cable is operating the throttle plate?

The Stromberg is a constant velocity carburetor meaning that the air going across the jet is the same speed at idle as it is at full throttle. Only the volume of air is different. There is only one jet and a metering needle varies the mixture as per volume of air so it is the closest thing to fuel injection you can get in a carburetor. This is a much more efficient carburetor than any carburetor you can buy, so it would not be smart to change carburetors. Unless you found a set of dual SU carburetors (which are also constant velocity carburetors)

First look at the throttle linkage to see if the throttle cable is moving the throttle. Then remove the four Phillips screws on the top and remove the top cover and inspect the diaphragm for holes. then carefully remove the piston and examine the needle to see that is is in good condition and be careful not to bend it. If that is ok, you need to remove the carburetor and remove the float chamber and check the needle and seat and the float level. The auto choke is a common problem on these carburetors but that is not your problem because if it were, it would not idle at all. There is a decel valve on the side of the carburetor but that too can not be at fault because if it were, it would not idle.

Howard

---------- FOLLOW-UP ----------

QUESTION: Thanks Howard

The cable is operating the throttle plate,,, I haven't insepcted the diaphragm but plan on doing that next, also this carb doesn't have an automatic choke it is manaul so I wouldn't think that to be the problem,,, if the diaphram is the problem will it come in a rebuild kik ?

Answer
A rebuild kit should include the diaphragm but ask your supplier before ordering if the contents are not listed. Most don't contain the metering needle because they have an ID marked on them and are different for different year cars. It should contain the needle and seat for the float chamber. Some of the other components may or may not be included like the decel valve. The jet is fixed and not replaced.

Howard