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MG Midget and Sprite Technical - Newby Carb & set up questions

Hi All
Ok- midget Mk III 1275 Resto.
Getting somewhere - she now starts on the key everytime. I cleaned out all the crud from the carbs etc and did the initial set of jet nut all the way to the top then two complete turns down.

She starts on the key but is now racing even with choke fully home. As this is my first midget, how do I proceeed to get the tick over right and also the fast idle. I have the haynes but really don't understand what I should be doing.
I'm not at all sure about setting the tick over ( top screw ?) or the fast idle screws ( one which abuts the cam attached to the choke cable ? ) - I have a gunson carb balancer and a colortune.
Thanks all for any help - I get good clear answers on this BBS!
cheers
colin
colin frowen

It's many years since I've adjusted twin carbs, but the procedure is pretty simple if I recall correctly. First get the engine warm. Once it is at normal temperature, make sure the choke tickover adjustment screws are backed off, so that they do not affect the running of the engine. Then:

1. unlock/disconnect the rod that goes between the two carb spindles so that you can tune each carb seperately.
2. Tune each carb so that the tickover is as good as you can get it. Try this link: http://www.checkthatcar.com/tuning_su_carburetters.asp
3. Balance the carbs by adjusting the throttle stop on each one so that the flow is identical. Then readjust tickover speed. Repeat the procedure until a good smooth balanced tickover is yours.
4. Re lock the connection between the two carbs and adjust choke tickover scres so that they are just clear of their operating cams.
SUs seem complicated when you first look at them, but really aren't. As long as the carbs are in good condition you should have no problems. Don't be put off by the number of screws just study the set up and work out what each screw does and treat each carb as a seperate unit to be adjusted until locked back together.
Hope that is a little help,
Graham.
Graham P

I don't know what the !!!! is wrong with that link, but if you google tuning SU carbs you'll get loads of hits!
Graham.
Graham P

from the horses mouth:

http://www.sucarb.co.uk/Technical.aspx
Doug Plumb

This thread was discussed between 03/03/2012 and 04/03/2012

MG Midget and Sprite Technical index

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