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MG Midget and Sprite Technical - SU Toolkit


Hello

Purchased this today having read up on the archive that it is the prefered option for Chris Kotting when synchronising the air. In past have used the gunson balancer but thought this might be easier (you can compare both carbs at one glance) & be more accurate (leaving air filters on).

Am lead to believe I need to use 1 round tube & 1 oval tube. Into the top of each you insert 2 loops of the wires. One goes into the oval tube fine but I think I'd need a sledgehammer to get 1 of the other wires into the remaining round tube! I have tried all 3 wires in the round tube.

Should 1 of the loops be smaller to fit in the round tube? Any advice would be appreciated.

Thanks
Gavin Rowles

have you got some pics.

personally Its hard to beat the old ash tray carb balancer...(I say tongue in cheek) as I can rarely find mine when I need it and end up using the rubber hose trick from carb mouth the ear and listen to the hiss for adjustment.

Prop
Prop

I am clumsy, and have always struggled trying to use the classic methods to balance twin carbs (I own about 3 or 4 different types of tools that I have tried over the years).

Finally, I bought a digital meter designed for motorcycle engines and tapped into the vacuum just after the throttle plates and dialed in my car so perfectly that the idle became more smooth than it had ever been. I have had my car tuned by several different experts over the years, but none of them ever got it as balanced as that electronic motorcycle tool did, because it is so sensitive, and relies on nothing arbitrary (and has no friction in its function, ideal for small displacement engines that don't draw a lot of air in the first place).

I was able to turn my idle down to about 600rpm (sounds so nice to hear it just "tick over" like that), and revs smoothly all the way through the RPM band under load in just about any gear.

So, my advice is: buy an electric motorcycle carb balancer, and never look back!



Norm "not usually convinced by 'modern, new-fangled' tools, but this time definitely was" Kerr

Norm Kerr

Hey Norm,

Bad Move on the 600 rpm idle

The oil pump needs at least 800 to 1100 RPMs (depends on the model year) for the oil pump to to do its job properly...AKA supply oil and oil pressure to the all the bearings ( I think ??? moss catologe will tell you which year needs what RPM is all based on the emissions change over ) other wise someone on here will know the proper RPM you need

curious...you said >>>> tapped into the vacuum just after the throttle plates <<<<<<

Im not sure I exactly know what you mean, is that the brass vacume ports that goes into the "Y" piece then to a hose to the timing chain cover?

Also did you leave the air filters in place?

Ive recetly purchased a set (4 in one unit) of motor cycle vacume gauges on the super cheap, but the instuctions are super vague and lack any therory

I was thinking of doing the same thing like your suggesting, but wasnt sure it would work without some kind of restrction or arbetariy metered hole over the mouth of the carbs

can you provide some extra info on what you do...thanx

Prop


Prop

Hey Prop, I'm jealous.

I could do with a set for my Honda 750/4
Dave O'Neill 2

Hi,
the balancer I used was a twinmax:

http://www.twinmax.co.uk/

easy to use, and very sensitive (actually, the sensitivity is adjustable, so you gradually increase it as you get the two closer and closer to "perfection"). A real boon for someone as ham-fisted as me for subtle things like this task.

To hook it up, drill and tap into the phenolic spacers. Though, I think that one could just hook up to the vacuum ports on a '70s era set of SUs (the two brass tubes that are normally "wyed" together to the breather on the crank case front cover on US spec 1275s, I don't know what was on UK cars). Because those ports are just past the throttle plates they should be a good, accurate source of vacuum, right?

Looking back, I think I was exaggerating about my idle speed. To tell you the truth, I didn't write it down, and it was so many years ago (once I got it right I never touched it again). Anyway, it was rewarding to be able to make it idle so smoothly at a low speed (anyone can make an engine "run" if they keep it at high RPMs all of the time, its the smoothness at low rpm where, for me, a good tune pays off, I think).

Norm
Norm Kerr

Can this be used to set up twin SU Carbs on my 78 miget?
C Carter

it can be used on any kind of mutli carb set up where you can hook it up to the manifold vacuum between the throttle plate and the head, but before the balance tube that runs between the two carbs.

On my motorcycle, I remove the (rubber) balance tube and hook it up there. But on an MG, the balance tube is cast into the manifold, so you need to tap in somewhere before the intake manifold (the phenolic spacers are the usual place - minispares sells spacers with the hook ups already built into them).

Norm
Norm Kerr

Gavin,

Do you mean this kit? :


http://www.mgaroadster.co.uk/su_carburettor_tool.htm
Adrian Jones


Hello Adrian

Yes indeedy.

Did you have to tweak 1 of the wires?
Gavin Rowles

Gavin

Sorry, I can't help, I don't have one. I saw one at anautojumble last year, but not even the trader could explain how to make it work - he had the same problem as you!

Adrian Jones

So...... assuming you know how to use it, is the considered opinion the su kit is better than the Gunson Carbalancer?
Graham M V

Gavin, I struggled getting the wires in for over 6 months and gave up, then I discovered (can't remember how now) that you need to crush the tube end that the wire fits in to make it fit.

Never had a problem since all though I am thinking of a Gunson gas tester for checking the mixture.

Hope that helps
Shaun
Shaun


Thanks Shaun.

There are 2 'round tubes' so I will do as you suggest & if I do balls it up will try fettling the wire instead.

Interesting to note that the SU people down in HANTS don't supply this kit anymore - I guess someone else has the licence. Also, the current kit is made in China!

Need to attend to the valves & ignition 1st before getting on to the noisy stuff.
Gavin Rowles

This thread was discussed between 22/01/2010 and 09/02/2010

MG Midget and Sprite Technical index

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