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MG MGA - Rebuild carbs

My carbs are in need of refurbishment (in particular the choke does not completely disengage which I am sure it is not just a "spring" problem). I need to decide if I send them off for refurbishment or whether I fit a refurbish kit myself (such as item 1 on www.mgocspares.co.uk/acatalog/MGOC_Spares_CARBURETTORS__MGA__301.html#topanch ).

Would the refurbish kit include everything that would be done by someone like the SU Carburettor company, who tell me they come back like new? And is it a fairly straight forward job to do myself?

The carbs are clearly old and tired, and I wouldn't want to strip down and refit, only to find that there is still some slack in the linkage, etc.

Many thanks



Graham M V

Graham
If all the bushes and Spindles are OK then refurbishing yourself is possible - but you won't know if they are Ok until you strip the carbs down. With the correct reamers and honing tools and the knowledge to use them it is feasible to do the spindles etc yourself. Personally I would rather have them done by Burlen as I would not be confident in my own ability to do the work correctly. Others more knowledgable than me on this forum should be able to advise
Paul
P D Camp

Paul is absolutely right, everything is straightforward except the spindle bushes. However, the spindles normally wear much more than the bodies and if the carbs are not too worn and the spindles have have not been changed in the past, you may get away with just replacing those. Drilling for the butterflies is a little tricky, but quite diy-able.

If you have a blast cabinet and a DIY plating kit, you can make the carbs look brand new. Beware there are "restorers" out there that do just that and replace jets needles and gaskets and pass them off as refurbished!

If you have the gear, refurbish yourself and know everything is done properly, otherwise use a reputable company like Burlen.

To start with, perhaps you could take them off, clean them and lubricate and set all the linkages etc. You should be able to sort the choke and get everything working as it should without the rebuild kit and in doing so you can examine the spindles, needles and everything else to decide if they need to be refurbished or not.

Neil McGurk

Graham,
I toyed with doing my own, but didn't have reamers or the plating capability. I decided to use Andrew Turner. He did a super job and i don't regret paying the extra. The carbs were set up almost perfectly for the first start.
Contact details are:
www.su-carbs.co.uk
Andrew Turner
7 North Witham Road
South Witham
Nr Grantham
Lincs
NG33 5PN
England

Tel: 01572 767665

regards
Colin


C Manley

I have rebuilt SU carbs a few times, and have posted a number of tech articles on my web site. In most cases a worn throttle shaft can be replaced with another standard size shaft, as the throttle body does not wear much.

When the throttle body does wear, a 0.010" oversize shaft can be installed. This requires drilling of the throttle body 0.010" o/s, not necessarily reaming, but it does require use of a drill press and machine vice. There is then another decision whether to turn down the shaft ends to standard size or to drill out the throttle arms (in which case they cannot later revert to standard size).

If you read other tech articles, it is possible to hand ream the journals to larger diameter and install bushings to standard size with no drill press required. Having gone the o/s shaft route once, I think I would prefer to install bushings and continue to use standard size shafts. This decision may depend on what machinery you may or may not have conveniently at hand.

As to the choke sticking on, this means the main jet tube is sticking the jet seals. This can be brought on by long term storage (maybe several months out of service). It is (usually) easy enough to cure by polishing the OD of the jet tubes and adding a drop of oil, even without disassembling the jet bearing and seals.

For a long term fix for sticky jets, I highly recommend installing a pair of Teflon O-rings (cheap enough) in place of each jet seal. I have used these in a few sets of carbs, running the ones in my car for over 100,000 miles in 12 years with no sticking and no dripping.

By now most folks understand I like to do things myself for the experience and for the confidence of knowing it is done right, and of course to same MONEY (and so I can explain how to do it for others). For some people only needing to do this once, or with more money than time available, it may be appropriate to farm it out, in which case I would recommend a verified competent rebuilder, whoever that may be (usually by good personal reference from prior customers).
Barney Gaylord

Graham, go for it yourself, list the bits you need and buy them. use the Moss catalog exploded dwg to help you not lose stuff (total of >200 parts for 2 carbs !)
Just been through it, not difficult stuff. Worn holes can be fixed by soldering in solid brass rod slices and re-drilling. But one of the linkage holes is meant to be elongated.
Art Pearse

As Barney states the sticking, that seems to be your big complaint, is a real easy fix. Unless your shafts are worn cleaning and reassembly is all an overhaul consists of. The linkage has a lot of looseness brand new. Without the designed in slop they would never operate smoothly. Some have gone to the effort of brazing up the "oversized" holes only to find that they then did not work.
R J Brown

Hmmm......I really appreciate the feedback. I am not an experienced mechanic, just trying to do as much as I can on the car to learn and also for the satisfaction of doing it myself. But reading the comments has convinced me that this is probably beyond me as I have no special tooling and haven't a clue how to ream, etc.

But you are right that the choke is my main problem. I would like to try what Barney has suggested but to prove my ignorance, I dont know what you mean when you refer to "OD of the jet tubes" and when you refer to Teflon O rings to replace the jet seals, I don't know which jet seals you are referring to. I have looked at the diagram in Haynes, but it doesn't seem to help.
Am I a lost cause and should I leave it to the experts? Either way thanks for your help!
Graham M V

Graham, don't be afraid! Download the Moss Motors MGA catalog from the www. It has a detailed exploded view, part numbers and description, and prices. You can't break anything by disassembly. As RJ says, it's 90% just cleaning and reassembly. You will save a lot of money and learn a lot. No special tools required, unless you have to insert bushes or ream oversize. But if this has to be done (maybe not) any good machine shop can do it.
The deliberately oval hole in the linkage is designed to permit the fast idle position before the jets are dropped to give a rich mixture, so don't interpret this a worn.
Art Pearse

I would suggest that you do one carb at a time. That way you can refer to the untouched one if you have any questions while reassembeling.
Ed Bell

OD is "outside diameter".
Neil McGurk

OK guys - you have persuaded me. Thanks for the encouragement. I will leave it until the winter really starts and then have a go.

But please look out for my desparate postings come November/December!!!
Graham M V

There's also the info available here

http://www.clancy.ch/Library_files/Tuning_SU_Carbs.pdf

This is a very clear and well written booklet from SU, which covers servicing, strip down and reassembly, and also how to check the bits are all OK and how to tune the carbs when you have everything back together.
dominic clancy

Thanks that really useful. Is it recommended that I buy new needles? I see they are not expensive
Graham M V

Check your existing needles, if they are not worn don't change!
Neil McGurk

OK I should have added provided there are the correct type, e.g. that your car (can be adjusted to) runs well through the rev range (not too rich or lean).
Neil McGurk

This thread was discussed between 12/10/2009 and 16/10/2009

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