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MG Midget and Sprite Technical - Midget MK3 Engine number + Carbs

Hello all,
I have a midget MKIII 1275 RWA. In this car is not the original engine. According to my Heritage Certificate the original engine has # 12V-587-2-L/2989. Sale destination North America. The # on the current engine is 12CJ /DA/H33231. On this engine are AUC870/871 SU HS2 carb's fitted. I have a donor midget wich also has the same carb's on it. (don's know that engine #)

I am currently refurbishing these Carb's and want to replace the Jett Assy, Jett bearing and needle (spring loaded) Can anyone tell what and where the correct parts can be found? My Moss Part Guide does not have this AUC870/871 Carb listed.

Can anyone also tell what the 12CJ /DA/H33231 engine is and should the AUC870/871 be fitted to this engine?
My donor car has a 25D4 Dissy fitted with vacuum advance and manual control. I think i have a 45D4 with vacuum advance (no control) fitted. can this setup work
Niek Lammerts

Hi Niek
Yes the 45D can and will work but if the curve is optimal you will only know on a roling road.
Or just try it out.
On my 1380 a 25D from a 850 mini worked best after a lot of trial and error

For the carb parts you can go Local
The MGworkshop in Monster has plenty in stock and can order anything at competative prices (and good quality) www.mgworkshop.nl will give you their adress.
Nice place to visit though I think you know Thijs?...
Onno K

Hi Onno,
Thanks for the reply. I will check their site. Sorry but i don't know Thijs. I live in Friesland and do not frequently go south :-). Can you e-mail me direct?, i wonder whats up with 1380cc in a Midget ?
Niek Lammerts

Niek, according to the SU manufacturers Burlen Fuel systems, those carbs are from a Riley 1.5, see here:
http://www.sucarb.co.uk/CarbEssentials.aspx?ProductId=9926
David Smith

Was that the real Onno replying? I'd have thought the real Onno would be too 'busy' having just got married and would have replied in dutch!
Daniel Thirteen-Twelve

Somebody's been changing tags!
Riley 1.5 uses H4 carbs, same as MGA. There were no HS carbs during 1.5 production.
AUC 870 is the correct spec for the 1.5.

All HS2 without waxjets use the same jets. You need the correct needle for a bias needle 1275 application, preferably whatever a 12CJ is (we didn't get them). Also match up the carb-crankcase vents. Early HS2 do not have the vents, later do. Bias needles extend over both types for a time.
I have never found need to replace the jet bearings, and I have rebuilt a huge number of carbs.

FRM
FR Millmore

@ David. I also found that part of the info, but a lot of things they list are not correct, jet, needle etc. So i think there is something else with the carbs. I mailed SU my tech.info and now whe wait :-)

I googled whole day and could not find anything simulair about the AUC870/871

Only thing i can add to this, is that on the float chambers there are 2 alu tags, one is AUD502R and other is AUD502F. Maybe it is a rebuild set with a "standard" carb body allong with car specific jet, assy, spring and needle.... I hope SU will let me know soon......
Niek Lammerts

Guess we posted on each other.
Don't know where you got the AUC870 number, if the tags are AUC502. Normal for sets is number/F, number/R
502 is early '72 US cars. Biased and vented. Needle ABC as stock.

FRM
FR Millmore

The AUC870 / AUC871 is casted on the side of the Carb's. The Carbs have the vents for crank case (trough Y tube)The labels are on the fuel chambers they say AU D 502 (not AUC502). The needle currently installed is the AAT, this needle is also in the carb of my donor car. (i got pictures, can mail them)
Niek Lammerts

additional to above posting. According to book: "SU Carburettors Tuning Tips & Techniques" (Brookland Books) The needle for an AUD502 would be CUD1017 (that is an AAT), spring=AUC4387 , JET=AUD9142
Niek Lammerts

Niek-
"The AUC870 / AUC871 is casted on the side of the Carb's."
Right you are, which is very strange, as that is the set reference number for the Riley 1.5 H4, by the BMC SU master book. One possible thing is that these numbers frequently have an electropenciled additional digit following the cast numbers. These are frequently very faint and sometimes missing. The AUC870/871 are the main body basic casting numbers, and machining differences for different applications would be denoted by an electropencil 4th (or more) digit. This was common on many SU bodies. If at the time of production there were no variants, then the fourth digit would be zero, but there would be little reason to write it - except for confusing us!

For future reference, these numbers on the body are casting numbers, not specification numbers, which are only found on the tags.

My mistake on the AUC vs AUD error.

The ABC needle is a US fitting (per Moss US), other markets are probably different, though the AUD502 specification number should cover the needle spec. Needles were sometimes superseded in the field, so it could have been a change either from ABC to AAT or vice-versa. Depends on the dates and reliability of the reference original source.

FRM
FR Millmore

@FRM, Thanks for the info. There are some differences in Europe and US cars and parts (moss.co.uk and mossmoters.com) They use different p/n for same parts. Also there are some differences in UK and US cars (i have an imported US MKIII)
So It took some effort, but we get there in time :-).

Niek Lammerts

This thread was discussed on 20/05/2012

MG Midget and Sprite Technical index

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