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MG MGB Technical - Intermittent is an ugly word . . .

My friend's problem has been solved (but not by me). His car would stall, usually after making a hard stop at a quickly changing light or when slowing to make a sharp corner. It would appear to have fuel and electrics but would not restart. After 15 minutes or so, it would restart and all would be normal. The happened perhaps eight times over a six-month period.

Finally, it stalled and failed to fix itself. It refused to start even after a considerable delay. It turns out that the aft carburetor piston was stuck in the up position. Why, no one knows. The piston has been sanded and lighter fluid used in the damper.
The car now runs beautifully.
Dan

Dan,

You don't say wheter your friend's car has SUs or Strombeg carbs

If your friend's carb stuck in the up position, it was probably dirt somewhere. I know that sounds obvious but the likely places are in the jet, between the needle and the metering orifice, or the between the SU piston (if applicable; Stromberg CD carbs are different - see later)and its housing.

I suggest you replace the fuel filter, blow out the fuel lines and clean the inside of the SU dashpot cover and the outside of the piston with cellulose thinners. Do NOT use any form of abrasive cleaner - sanding may well rapidly kill the carb. The fluid in the dashpots should be a light engine oil, say SAE30. Some people use ATF fluid. (I hope yopur 'lighter fluid' wasn't cigarette lighter fuel!)

As far as Stromberg CD carbs are concerned, I have experienced sticking when the carbs were re-assembled in a different orientation to the manner in which they were correctly assembled. Also the rubber diaphragms in the Stromberg carbs have a finite life - sometimes short. Again keeping it all clean is the way to keep it working properly.

A LITTLE light lubricant on the joints helps but too much just attracts dust and dirt, which with the oil makes a nice grinding paste!

Another thing which might cause this problem is a temperature compensation device. Some UK cars - 1500cc midgets for example - used devices caused waxstats in the jet mechanism of their SU carbs; the obkect of this device was to move the jet up or down to compensate for changes in operating temperature. They didn't have a good reputation in the UK and many people, including me, converted the carbs back to fixed jets. There may be a similar device on your friends carbs.
Peter H

This thread was discussed between 25/05/2002 and 26/05/2002

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