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MG Midget and Sprite Technical - Getting an engine set up

Hi

I need some advice of setting up an engine please (948cc Sprite, twin 1 1/4 SUs, engine contents a bit unknown, did have two different needles [!] from PO who has done other bad bodges, so now on two standard MkII needles). Got it going, but ‘slow’ running is about 2,000/2,200 revs - got the airflow matching in the carbs but cannot adjust the carbs down to lower revs.

Starts and runs quite happily stationary for 20 mins, and took it round the block - bit gutless as revs are a bit odd for the gears. Plug colour fine - I had wondered if it was too rich.

What next in what order - get it warm, adjust the tappets, then check timing and then disconnect the carbs and see if can get them running slower while still balanced airflow? If I do all that and still running too fast what next? Try different needles?

Thanks
Mike

M Wood

Mike,
as you say, it's back to basics with this one.
1, tappets
2, timing
3, compression check
4, remove and plug any crankcase breathers fed to the carb/inlet manifold.
5, disconnect the carb inter link and close the butterfly's to ensure they are able to restrict flow down to zero.
If it's still running with the butterfly's closed you have an air leak somewhere.

I presuming you have twin HS's and not HIF?

Best of...
MGmike


M McAndrew

ETA: my typing was too slow but I think my post still stands.

You could check for anything catching on accelerator pedal or cable or carb linkages or choke cable, air/vacuum leaks - but best to also start from scratch.

Check and adjust as required valve clearances cold, then check and adjust as required CB points, plugs, timing and last adjust mixture/carbs.

You'll need to reset carbs individually for balanced idle airflow with linkage disconnected then sort the mixture on each carb and after balance the carbs at idle and fast idle.

I'm not good at the setting the carbs up but can put up various different methods including from 'the good book' and others (lifting the pins never really does it for me but I think it's more noticeable with worn carbs).

Idle and fast idle revs are what suits the car but 2,000/2,200 revs is very high even for fast idle.

Plugs colours are never a great indicator particularly on short tests or when the car is given a blast.
Nigel Atkins

Mike,
I've just thought, it might be a good idea to post up here some good quality photos of your carbs. linkages and controls as a few long term owners on here, including myself, have thought they have standard carbs/linkage/control set-ups when they weren't and detailed photos have highlighted this.
Nigel Atkins

A fast idle generally indicates air getting in somewhere. Have the throttle butterflies been out? If they aren't positioned just right they don't completely close and even the tiniest extra bleed of air round them will boost the idle by a surprising amount. Don't ask me how I know.
Mike Howlett

Hi all

Really helpful advice - I have now got the engine to run at 800rpm. Think there were air leaks via the inlet manifold and the linkage was the wrong way up! Changed the inlet/exhaust gasket and made sure manifold as well as carbs to it correctly tightened up. Changed the old needle valves. Put in new clean plugs. Adjusted the the jets down 12 flats from level with the bridge and bingo, it started first time.

Now I can do all the above checks/settings you advise.

You all rock!

Cheers
Mike
M Wood

Well done.

If you look in the Archives here there'll be at least three different way of setting up the carbs and you can find which suits you best.

Do bear in mind the engine and carbs are two of the less important things on the car, priority to checking brakes, steering, suspension (all three include tyres) and all safety electrics.
Nigel Atkins

This thread was discussed between 05/06/2022 and 24/06/2022

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