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MG MGB Technical - Sputtering When Cold

My car is a basically stock 1973 MGB. It runs great, except when it is cold. When it warms up it is fine. It never fails to start on the first try. After it starts when cold it will idle fine. However, if I drive it, it has no power and sputters and chokes. No matter where I set the choke - from full on to full off - it makes no difference. I never have this problem during the Spring - Summer - Fall - only during the winter. Suggestions?
Robert Browning

How's your idle speed? Is it stepping up with the choke?
.

Yes, the idle speed steps up with no problem. It is just when I am trying to accelerate that it starts sputtering and coughing.

Robert
Robert Browning

You can try richening the mixture a bit to make up for the denser cold air. Sputtering and choking are symtoms of lean mixture even in warm weather.
willieL

Hi.

It might be worth trying spark plugs that are one grade hotter in winter.

Another possibility is carb icing, which is more common than I believe is generally realised.
Maybe late model air filter cans with the elbows that collect warm air from the vicinity of the manifold would help ? (again for winter only).

Don
Don

I noticed tonight when I went to start the car, that when the choke is full on, it is blowing what looks likes oil or black stuff out of the exhaust (but the car does not use any oil). It is enough that it splatters on the wall of the carport, three feet behind the car. However, when I pull the plugs they are clean.

Suggestions? Comments?
Robert Browning

The black is soot from the choke being engaged.

Does it run better if you leave it partially choked for longer than you normally would?
.

It might be worth checking the spark advance. Put a timing light on it and be sure the distributor is advancing. Although the fact that your plugs show no smut would make me think it is not that.

Still, sometimes an engine warming up can cause a distributor to act differnetly than when it was cold.
I have fiddled with a lot of carbs in the past only to find I had an igntion problem. Good luck.

John in Music City
John Lifsey

The distributor is less than a year old, but I checked it anyway and it seems to be operating fine. As for running better if I leave the choke engaged longer, it seems that I am having to constantly adjust the choke for different speeds to keep the car running. With the choke engaged, at any position, when trying to drive the car just has no power.

Robert
Robert Browning

John, I have similar problems with our 80B. It may help to install richer needles in the carbs, but what I did to help my car in the winter (I have an early twin SU set up with the early exhaust manifold) is I installed a 190 degree thermostat, one heat range hotter sparkplugs as Don mentioned (remove when the temps get warmer) and thirty weight oil in the carbs. My B warms up a lot faster and the hesitation is much less. Yes, I still keep the choke on longer, but the hesitation is considerably less.

Mark
M Whitt

This thread was discussed between 29/01/2007 and 31/01/2007

MG MGB Technical index

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