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MG MGB Technical - HIF Carb needles

I would be grateful if anyone can help me with a question I have about SU HIF carbs as fitted to the 18V MGB engine (as fitted in my TD, standard camshaft). There seems to be three needles listed; AAU, ABD and ACD, and possibly also AAE and AAL. I would like to know which needle gives the weakest mixture, or the optimum miles per gallon, ignoring the effects of exhaust emission control or air filters as these are no longer fitted to my engine. Thanks for any advice.
Roger Wilson

Roger, You can enter the needle letters in the chart in this link and do a comparison. Use the .090 needle interface.
http://www.teglerizer.com/suneedledb/index.html

Clifton
Clifton Gordon

Try http://www.mintylamb.co.uk/suneedle/, allows you to visually compare five needles. ACD is the weakest, although there is only a significant different in the upper half of throttle range (not revs as indicated on the chart).
Paul Hunt 2

Thanks to Clifton and Paul (whom I recognise as helping me last year) for pointing out the two web sites. I did indeed find that ACD is the weakest, and that is what is in the carbs on the MGB engine in my TD. Paul, I did the checks you suggested, including changing some shaft seals, and the fuel consumption improved from, I think, below 20 mpg to just over 27 mpg. However, I understand that some MGBs get over 30 mpg, and that is what I was hoping for. I haven't actually tried any other needles, and since I now only do about 1000 miles per year, at 27 mpg perhaps the problem isn't quite so acute. I am also told that I shouldn't drive my car wearing diving boots, but surely they don't make any difference!
Roger Wilson
Roger Wilson

Ah, driving technique is the biggest variable in fuel consumption, and lead-footed drivers get the worst :o) I get around 30 knocking around with a certain amount of gusto, but on a long steady run to central France and back got closer to 40. On a careful run back from Le Mans one year (I had a cooling system problem) I got 340 miles out of a tank and still wasn't empty, and that was in the V8!
Paul Hunt 2

My 73 MGB HIF's had ABD needles as standard. After fitting the K&N "Bob" filters (see http://www.cibolas7.net/17963.html & http://www.hotelling.com/mgb7.htm) the mixture was noticeably lean and I changed to AAA with significant improvement in pickup and acceleration.

Barry
BJ Quartermaine

This thread was discussed between 16/10/2007 and 20/10/2007

MG MGB Technical index

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