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MG MGB Technical - dual hif carb problem?

Have got my 80B running a bit after adding new points, dist, rotor and plugs. Runs like crap and I suspect carbs. In diagnosing problem, I found once I get car running and keep it going by pumping gas repeatedly to get it warmed up, it will barely idle. Upon idle, if I pull first plug wire (next to rad), engine works worse, same with second wire. However, when I pull 3 & 4 there is no change in idle. Question is,,,,Would this indicate the carb closest to firewall is not feeding back 2 cylinders? Is that how they distribute fuel? If so, what steps should I take to remedy?
A MacNeil

Update: Took air cleaners off, lifted the plunger in both carbs. On the carb in question it appears the needle guide has dropped down. Is this possible? And can I repair it without special tools?
A MacNeil


Yes, the rear carb feeds cylinders 3 & 4.

The carbs don't generally go out of adjustment, don't tinker with the linkages at this stage.

Do change or clean the air filters as appropriate.

Dispose of any old fuel and supply new if it has been standing for more than a few months.

My next step would be to check that the carb pistons are operating correctly. Make sure that the dashpots have the correct quantity of the correct oil and check that when pushed upwards with a finger they rise with a constant and equal resistance and fall smartly when released. (remove the air filters for access).

If the throttle butterflies still have the little spring loaded valves fitted solder them up or replace the butterflies with blank ones.

Do the throttle spindles flop about in their bearings in the carb castings ?, this is a fairly common problem and makes accurate setting up difficult if not impossible.

If you still have probs you may have a sticky float or float valve. How do the plugs look ?.


Hi again.

You got to 'Submit' before I did...

It sounds as if the screw that holds the needle in place has become loose.
Removing the carb piston is quite straightforward without special tools, but I wouldn't get the screwdrivers out without at least a Haynes manual, or preferrably the 'official' manual as the carb is a fairly delicate precision device.


Thanks. It was the screw that holds the needle guide in place. 10 mins and my car is like new. Now.....1 month late, but I'll "B" gone on the road till my next mis adventure. Car sure feels good.

Thanks for your feedback

A MacNeil

This thread was discussed on 29/04/2006

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