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MG MGA - Carb Tune and Idle speed

My 1600 Mkll runs well, but has never idled smoothly since I bought her 2 years ago. I have had a couple of tries at tuning her - timing, carbs etc, but she is reluctant to idle without shaking herself to bits at below about 1100 rpm. I had the same sort of problem with a TF a few years ago, and I sorted this out with a carburettor rebuild, so I am about to do the same with the A - the cork jet seals are soaking in oil right now. But I can't find anywhere in the workshop manual that says what the idle speed should be. Any ideas? What speed does your A idle happily at? Incidentally, my A has Lumenition ignition fitted and an alternator - will this affect the timing? Thanks, Adrian B.
A Bennett

Adrian

I normally set my idle at 800RPM. The electronic ignition and alternator make no difference to the timing.

I am always a little cautious about giving advice without knowing more of the symptoms or what setting up has been done previously. Whilst your carbs will no doubt benefit from an overhaul and resynch, I always have it in the back of my mind that many 'fuel' problems are in fact electrical (timing). I will be interested to see where you end up on this one.

Steve
Steve Gyles

Hi Adrian , mine is at 750 /800 and idles quite smoothly (most of the time)


gordon
g c pugh

My A will happily idle at much less than 800rpm. However when doing so, I have a few problems. 1) when I depress the clutch, the rpms drop a bit further causing it to stumble 2) the charge light starts to glow a bit and 3) it is a bit hesitant to increase the RPMs when the throttle is depressed 4) when it is summertime (is it ever going to get here?) after I have been driving at speed, the lower idle setting makes it idle too rough and almost die. As a result, I tend to set the idle at 900rpm or a bit more. It is much happier there. Besides, I don't spend too much time at idle.

Chuck
C Schaefer

My car idles fine at about 800 to 900 rpm once warmed up. I did have similar symptoms to yours and they went away after replacing worn throttle shafts on the carbs. Good luck!
Tom Heath

Hi Chaps, Just thought I'd report back after rebuilding the carbs. It shows that you just can't trust other people's restorations!! What I found when I stripped down the carbs was as follows:
1. Two different carb needles - very different profile and length, one was a 6 and the other a 9.
2. Different jets - both marked 6, but one with a larger hole.
3. Different length piston springs.
4. The carb flange to manifold gaskets were too small, restricting the porting by about 1/8 inch all round, and presumably interrupting the airflow.
naturally, the car is much smoother now, and idles quite well at 800-900 rpm. The throttle shaft springs were not quite strong enough to return the throttle to it's stop every time, so I loosened the clamps and rotated the springs a bit to increase the tension, and that seems to have done the trick. All I need now is a fine day to give it a good run without freezing my n**ts off. Cheers, Adrian B.
A Bennett

Good work Adrian - it's amazing what DPOs do to their cars - cheers Cam
Cam Cunningham

This thread was discussed between 05/03/2008 and 13/03/2008

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