MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Balancing SU's -Lucky?

Would be interested to hear if what I have done makes sense! It seems to have worked and was so easy but could well have been more by luck than judgement.
I have always been afraid to play with the carbs as I once completely screwed them up and had to call in the experts. But I think I discovered a simple way (though I am sure not a perfect way), to get them to roughly sing of the same hymn sheet without too much tinkering.
Keeping the connecting gear, etc. in place, I turned(clockwise) one of the carbs idle screw very slightly to see if the engine picks up pace. In my case it did so I then turned the screw on the on other carb. At first nothing happened but I continued until that one made the engine pick up pace. If the first had had no effect, I would have kept turning it until it reached the point where it did. The idea was to reach a position where both screws are at the point where any small clockwise turn for either will speed up the engine. Then very carefuly, a bit at a time, I loosened of each screw in turn to get the idle speed down to that required.
As I say, it seems to have done the job for me. Was I just lucky? (I realise i must look at the mixture next and then rebalance). Thanks
Graham V

Graham,

I think what you have done is correct, except it is step two and you skipped stem one. So, if you have the airflow balanced, it was luck.

Just because you have both idle stop screws at the tip point does not mean both butterflies are open the same amount.

I start by backing the idle stop screws out until they have no effect. Then I loosen the clamp that ties the two shafts together. Then I hold both butterflies closed and tighten the clamp that ties them together. That way, they have a common starting point.

Then I do what you have done with the idle stop screws. Next, if I had a Unisyn, I would check the flow with that.

Charley
C R Huff

Graham by the sound of it all you have done is balance the carbs at tickover. You are supposed to loosen off the interlocking mechanism then balance the airflow (as you have done basically with the shafts locked together). There is play in both carbs and the interconnection shaft and you need to make sure after you have balanced the airflow through both carbs that you lock them together so that they pick up at the same time. This is very easy if you do it as per haynes and thousands more techniques.
Robert (Bob) Midget Turbo

Hey Graham,

Here is a great site, super easy to understand

Prop

http://www.mgcars.org.uk/cgi-bin/gen5?runprog=mgoc&p=emg/basic4.html

Prop

Well I am pleased that at least I am on the right track, but had guessed it wouldnt be that simple! I have Haynes but I find it all a bit complicated. With most things, I would just start and hope it becomes clear as I go along, but with this, I am worried about mucking them up completely (like once before) so am trying to fully understand what I'm doing in advance.
So could I double check please at risk of sounding very thick?
I first loosen the clamp on the linkage and then I adjust the idling screw for each carb. Not sure what I adjust them to, so would it be a good idea if I buy a gunsons Carbalancer for this bit? If so, I assume I just adjust each idle screws until I get the same reading for the carbalancer for both, and then retighten the linkage clamp?
I assume I then do what I described in my earlier post (adjusting each screw with linkage connecred until I get to the "tip")?
And then I should adjust the mixture using the nut underneath? I thought it best to get a colourtune for this bit.
I then repeat stage two to re-adjust idle speed (i.e. without loosening linkage) if it needs it?

Sorry if it is obvious but would be really grateful to hear if that is correct. Also, when (if at all) do I need to touch the other idling screw. I think its called the fast idle screw, (I only have one of those screws)?
Very many thanks, Graham
GrahamMV

Hey graham,

unless you got $400 to kill and help the economy, I wouldnt buy a gunson.

Did you look at the tech artical I posted for you above.

prop
Prop

>>>>>>>unless you got $400 to kill and help the economy, I wouldnt buy a gunson.<<<<<<<

just a piece of rubber hose about 1 inch in diameter, and a good ear is all you need to balance the carbs

you can also do it with a 10 dollar vacume gauge but I have never done that, Ask Danial 1312....he can give you soe insight on how to do it.


Prop
Prop

You are only covering half the task of setting up the carbs.

Are your jet heights correct?

Do your dashpot pistons fall at the same rate?

Are your float heights the same?

Are the throttle spindles worn? (if they are, you are wasting your time anyway...)

Finally, is your Ignition timing correct? (this should be set up first).

Like mentioned above, you are on the right track, but it takes experiance to get them right.

Keep trying though, you'll get there in the end.

Mark.
M T Boldry

Graham, all you have done is set the idle screws, you haven't done anything regarding setting the mixture, that is done with the large nuts underneath the carbs.
As Mark says, it's pointless touching the carbs until everything else is set correctly. Then you can start playing! Mixture first idle last of all.
Find yourself a decent tuning book for Sus, I'm sure you'll find something on Google.
Good luck
John
JOHN HALL & JULIE ROBERTS

anything by "das hammel" is good


prop
Prop

Graham,

John Twist has a two part video that might help?

http://www.youtube.com/watch?v=7GRAcqDySog

http://www.youtube.com/watch?v=60Bj_2cZQnc

Regards,

Larry C.
Larry C '69 Midget

Oh dear. I knew it was much more difficult. As I am frightened to screw it up completely, I think its best if I just tinker a little bit at a time and slowly learn and get used to them. Thanks for the link to John Twists video, that was informative.
GrahamMV

Yeah,

My house electric has been giving me fits also, it keeps smoking when I plug something in and hissing in all the swithes and recepticals, and I get shocked everytime I touch a door knob, I ve been messing with it, but not sure what to do....I like your thinking graham, you said....

>>>>>>Oh dear. I knew it was much more difficult. As I am frightened to screw it up completely, I think its best if I just tinker a little bit at a time and slowly learn and get used to them <<<<<<<<<<<<


sounds good, I bet it will work for me also.

NOT!!!!

Sorry graham, just trying to make a point, not being mean spirited, Unfortantly you have walked into a tar pit, a mouse cant drag you out.

what im saying is you cant do a little bit of carb adjustment over a long period of time, it has to be all at the same time, doing this a bit at a time can have costly and permentaly damaging experiances, from burnt valves, warped heads, cooked pistons, carbonised exhaust systems and engine bearing failure with rod thur the side of the block kind of damage....and thats just in the 1st 500 miles

Ither call one of our local BBS friends in the area to help out, or take it to a shop and have them sort it, or go back to the above link I posted for you and take a day and do it right...

if any thing just get it back in tune, where it should be...if there are shaft, needle, float problems, hey thats what we are here for, all of use will figure that out with you.

Prop...once a lowly servent slave, now I lord over the dark forces of the SU, victory is mine!...Prop
Prop

Prop,
I must defend myself here. I dont want to take my car to a specialist, as I WANT to learn how to do these things myself. For me it comes as part of the package of having the car and part of the fun is the learning plus also the satisfaction of getting it done.
The car runs well enough to drive but not as well as I would like. The little bit of tinkering I have done so far has done three things. First I now understand just a little bit more about how the thing works, second I am less frightened of it, and third it actually idles better (granted more by luck than judgement). That can't be so bad can it?
I have read the article you kindly referred me to and lots more too. So I am learning. But bit by bit.
I am a novice at all of this, but want to learn, and that is bound to mean making a few mistakes along the way.
Sure if I knew someone nearby who could show me and I could learn from, that would be perfect, but unfortunately that doesn't seem to be an option.
I know you are only trying to help and save me from a disaster, but as I said, I want to learn for myself and get the satisfaction of doing the job.

So, I have bought, cheaply through ebay, a carbalancer (I know a tube and ear does the trick but from what I have read the carbalancer is much easier for a novice), a timing light and am about to get a colour tune kit. The whole lot for just over £50 which wont break the bank.
Prop, I appreciate your concerns, but hope you can see my logic.


GrahamMV

Makes good sense to me Graham

there are a few Spridgeteers around Middlesex too and the local (londinium) branch of a Spridget club will be at the ACE cafe tonight if you want to get some advice and such

£50 for that package, sounds the real deal-ish

Bill sdgpm

Thanks Bill.
I would love to go down to Ace cafe but can't make tonight. Is it on the 12th of every month?
Graham V

Nah, 2nd Tuesday..

Which happened to coincide with the London International Wine Fair ;-) Too pissed to drive...
Toby Anscombe

A fair-ish excuse

I wondered where you'd be

Some very very nice cars there too

This will be familiar to MASCOT readers...




Anyway, 'nuff thread drift. Graham keep in with the locals to you on here and you will soon pick up what you need to know.

perhaps I'll post a couple of piccies on General


Bill sdgpm

Graham....


Thats definatly the way to go, altough Id dis agree with the tube trick....definatly easier, getting the spare carb is perfect idea

At one time in my life the Su was a product of dark satnic art, to be feared, having been down that road, and spent alittle time with them, I have nothing but love and admiration for the little guy, they really are a simple carb to learn about, you will pick it up in no time, Just remember its a mechanical device, invented designed and manufactured by humans, not alian warlords in a distant galaxy.

That said your 3 best friend are....This BBS, Akowladgeeable friend, and any book on Su carbs by "Das Hammil" (5 books I think)


BUT,,,,BUT,,,BUT, BUT!!!

Please be careful, when doing this on your car,,,do ***""ALL""*** the steps at one time before driving, huge failure WILL happen if you dont

Closing NOTE ....

To John Mangles of All British car repair in St. louis,Mo. who is always lurking about here in the creavis and shadows of this BBS, Thank you for letting me pester you with many phone calls, and Vists to your shop to talk about the neuances, theorys, and practices of the SU Carb.

Prop
Prop

Graham,

Back to the John Twist (youtube) post I listed previously. You should notice a smaller box to the lower right of the page which lists related links on actual tuning of SU's.

Hope that helps,

Larry C.
Larry C '69 Midget

Larry,
Thanks. The videos are really informative. Have looked at 3 by John Twist and it explained a lot. Appreciate you pointing them out, thanks.
GrahamMV

This thread was discussed between 10/05/2009 and 14/05/2009

MG Midget and Sprite Technical index

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