MG Car Repair/RPM Fluctuation 1979 Mg Midget
QUESTION: What causes, and how to fix RPM varia-
tions when engine idling?
ANSWER: My thought is a leak on the vacuum
Side of the engine intake. Check the intake manifold gasket and any connections, or ports, hoses, etc.
---------- FOLLOW-UP ----------
QUESTION: This problem has occurred a couple of times before, and every time that happens my mechanic keeps adjusting or sometimes even rebuilding the Carborator. and then the car works fine for some time may be a year (usually the car is driven for no more than few hundred miles per year) or so. And then the idle variations or surges starts again when the car is at idle or while driving.
What parts in the Carborator. could be bad and cause that?
This is a difficult one for me so you may want to resubmit your question to the Question Pool and see if anyone else may have some ideas. Without actually examining the car this is tough. I would say if there are no vacuum leaks on the intake side of the engine plumbing, I have seen and experienced with my own cars - due to the E-10 or E-15 gas they are selling now. Many fuel system problems are occurring particularly in cars that sit a lot and are not driven regularly.
This new gas can really mess up carbs and fuel pumps when sitting as the ethanol attracts moisture, the gas separates quickly and gums things up in general. Try carb cleaners in the gas and various gas stabilizers sold in the auto parts stores. Then run the car for a 100 miles/several days in a row and see if this helps.