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MG Midget and Sprite Technical - Carb choke adjustment

Seem to have larger SU carbs fitted to 73 RWA. Lord knows their origin, but defo not OE. The choke linkage at the base of the carbs connects to the jets in the normal manner and lowers them when choke is pulled, but there is no mechanism to simultaneously adjust the throttle on choke. ie no choke cams

However, engine stalls on choke, but a bit of throttle seems to work. Thus, do I simply fiddle about with the position of the choke cable pulling on the linkage until it is set right?
Mark O

I had similar problem, and used SU carb manual to sort out where and how to adjust the tick over (mine just didn't tick over at all when I started it first after 12 years storage) to about 1000 rpm. Now fine. Send e-mail address / link to either my e-mail address or post on here and I will send it over (its electronic not on paper). Its got some great background info re cars and needles etc. in it as well.

Cheers, Dave
Dave Squire - Notts

Dave Squire - Notts

it might be a good idea to put up a photo of the carbs if they're not standard - and a photo of the engine bay as there may be other things not as standard

well done on getting your profile and photo up but please get that Handbook and see how to stow the hood properly or you risk damaging the plastic windows

the Handbook also tells you how to set the (standard) carbs, how to properly work the heater, what's required to service the car and how to do it and on, and on
Nigel Atkins


You will be delighted to learn I discovered a brand new handbook last night amongst the mass of paperwork that came with the car. Excellent info on setting the carbs, but of course applies to standard carbs only. I will see if I can get a pic up.

Hood is now - hopefully correctly stowed - under a tonneau....old eBay pic Nigel - all I have presently.

Dave - I will have a root about as somewhere I too have an SU manual. Just seems clear on the carbs that only jet position can be adjusted - which may be fine
Mark O

the Handbook carries loads more info, give it a good read and refer to it regularly as it help and save hassle and give correct information - I'll post only error and updates to it later, there aren't many

that old Ebay photo and the fact the Handbook is brand new might suggest that like many (even long term) owners the previous owner may not have known all about the car and how to operate it and full servicing requirements (like oiling those old worn dissys and lubing the cam for those nasty CB points)

generally one of the worst things about classics is the previous and present owners but you seem to be keen to break this cycle which will make the car better and more enjoyable - and more reliable

you'll be glad to know even with the photo I'll know nothing about the carbs so will have to leave that to others :)
Nigel Atkins

Dizzy points easily sorted via 123 ignition fitted!
POs - agreed, nail on head here I think.

So far before carb tinkering

New slightly colder plugs
New silicone leads
New sports distributor
Valve clearances checked
Good clean of all tubes

Pic should tell all...

Mark O

yes I thought you had a 123 but as usual couldn't remember for sure

plugs (usually) NGK BP6ES

tappets, plugs, timimg, mixture in that order

more important than engine stuff always:
. brakes - fluid, pads, flexi-hoses
. tyres - replace if old, hard and little used regardless of tread depth
. suspension - bushes often overlooked
. lights and windows (see and be seen)

also to help, the 36k-mile service or check up, thoroughly cleaning the waterways of engine block, heater matrix and radiator

and change and upgrade of g/box and r/axle oils
Nigel Atkins


for you - and my many admirers and fans on here :)

Amendments to 1973 Handbook

There’s only one error the ‘non-believers’ on here have found and that is that for our later cars with the Triumph type steering racks although there is a note on the previous page on the Recommended Lubricants table it shows oil instead of grease (although Mark Boldry still prefers to use oil in these racks)

These are the required updates I’ve noticed plus some of the service items intervals may now be extended
with the notable exception of greasing the front suspension as below

Tyre pressures (145/13) – below is +2 psi, some try up to +6 psi
• Normal car weight – Front 24 psi – Rear 26 psi
• Maximum weight – Front 24 psi – Rear 28 psi

Tyre wear indicator
• bars at 1.6 mm

Brake and clutch fluid
• DOT 4 is generally used now or even DOT 5.1 (note five point one not DOT 5)

• modern 35 amp glass fuses will fit but are a very slightly different size compare with the original glass fuses of 17 amp continuous/35 amp blow rated

Replacement bulbs
• Reverse – all markets except France - 21 watts, GLB 273
• Number-plate lamp – GLB 989
• Side marker lamp, front and rear – GLB 989
• Luggage compartment lamp – 5 watts, GLB 239

Spark plugs
• note; although spark plugs will last a lot more than 12 months they don’t last for ever and can be passed their best whilst still looking fine so bear that in mind

Engine oil
• 20w/50 was and still is the grade of oil used generally but oils have improved greatly since the cars were new so other grades could be considered and semi and fully synthetic oils

• as an alternative to clean engine oil you can use Zenith S.U. Damper Oil (SAE 20)

Rear axle oil
• you can use Castrol Axle EPX 80W-90 (GL5) or better still refill with Castrol Syntrax Longlife 75W-90 note; old E80 and 90 was GL4 and some insist you must use GL4 despite the fact for many years you got GL5 anyway! another frequently debated subject here

Front suspension grease nipples
• every 3,000 miles or 3 months and just before MoT
Nigel Atkins

This thread was discussed on 15/08/2012

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.