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MG MGB Technical - Do I need to Change Needles

I have followed Peter Burgess with a few mods, taken off the middle silencer, slight head mods and fitted K&Ns.
However he states that the HIF carbs should have the needles switched. My car seems to be running OK, is it best to change needles anyway?


Generally if you increase the breathing you will need a slightly 'richer' needle or you will experience flat-spotting at wider throttle openings even though the mixture tests fine with the lifting pins at idle. If the car picks up well at all rpms and throttle openings, and the mixture is correct at idle, you don't need to change anything.
Paul Hunt 2

Paul thanks again for your help, ive just run the car and your right there is a slight delaty at aboyt 3-3750, the idle seems OK, but its never idled that well anyway in 17 years!!!

To rich it up which needled do you reccomend, its a 1974 chrome with HIF's.


A rolling road will give you an accurate answer but the rich needles listed in your handbook will not be far off.


Are you running the K&Ns inside the cooper cans? I run mny 73 with HIFs with stock filters with no cans, and needed to change to AAA needles. Works perfectly now. There seems to be a definite difference in flow without those cans. Probably the most important thing is to make sure you retain the roundoff plate that is between the cans and the carbs, no matter what you do.
Erick Vesterback

UK cars got HIFs for the 74 model year with AAU needles. AAB are steadily richer until just after mid-way when they drift back towards the AAU, and the top three stations are all the same size. AAM similar but not so rich, and only the top two stations are the same size. AAA is also slightly richer up the range to mid-way, then gets closer to AAU, but goes weaker than AAU for the last two stations.
Paul Hunt 2

This thread was discussed between 31/03/2008 and 03/04/2008

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