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MG Midget and Sprite Technical - Twin SU Balancing and set-up

Hi

I have a 79 midget with a 1500cc engine i want to set up the carbs and was wondering if there is anywhere where i can get abit more information on the best way to do this? I have a haynes manual is this what everyone else is using?

Also i want to balance the air flow i have seen the gunson balancing kit, is this any good or would you recommend a different bit of kit?

Thanks

Rob
R Johnson

For balancing, I prefer to use the piece of tube in the ear routine and listen to the airflow into each carb.

The Haynes manual is useful, although if you search the archives, you will probably find more detailed instructions there.
Dave O'Neill 2

Also, do a search here for this topic. Lots of discussion in the last few weeks.
Norm Kerr

Most important thiong is to make sure ignition and everything else other than carbs is right first. No point in trying to tune a fault somewhere else by adjusting the carbs, yet many do!

Next thing is to check that the carbs are in good nick, especially no play in the throttle spindles. if there is they will leak air and make balancing difficult. If they are nice and tight and ignition etc are all good, tuning carbs will be a doddle.
Paul Walbran

Here's my take on the process here: http://www.mgparts.co.nz/twincarbs.html
Paul Walbran

TBH - it's fine trying to learn from a book, but, your best way to learn is to do it with someone who really knows how to do it - that way you get to know what's "right".

Otherwise - buy one of the many equalisers on the market and save yourself tonnes of time ;)!
rachmacb

You need to have mentioned the engine needs to be fully up to temperature. That's at least 20 minutes driving on the road before you start to adjust the jets or spindles.
F Pollock

Rob
In answer to your question, I think the Gunson carbalancer is brilliant. Makes that part of the job very easy.
Graham V

Use a piece of tubing its much more fun. A piece of rubber fuel pipe will do about 2 foot long. Hold one end right up close to your ear and the other end right into the carb mouth touching both the bottom of the carb venturi and also the base of the dashpot. so in as far and as low as it will go. Swap it over between each carb a number of times and listen to the relative level of hiss. great fun :-) and cheap as chips.

In my humble opinion people put far to much in store to balancing carbs at idle it is not that critical and as soon as you put your foot on the pedal makes no difference to anything.

What I would recomend though is opening the throttle gently and watching the dashpots rise in tandem through the carb mouths, check they rise up and fall together identicaly, if one leads the other then adjust your linkages.

cheers

Ben
Ben Brown

"makes no difference to anything" - au contraire! The balance between the two carbs makes a large difference in the smoothness of the engine at all throttle positions. The balance is only done first at idle because it is the easiest place to start. Then it must be confirmed at several more positions to confirm that it is still balanced, and some averaging is in order to find the best fit.

In the end, a car may run ok without this being done very well. But it will sing once it is done properly.

My "tin ear" was never able to get anywhere useful with the tube to my ear, but with a sensitive balancing tool I was able to dial them right in (and able to see just how far they were out!).


Kind of like having your bottom end balanced in an engine rebuild. It doesn't seem like it would matter until you do and you feel the difference!

Norm "smooth running" Kerr
Norm Kerr

I have the Gunson, but I find using a hose easier. The whole thing is really quite simple once you understand how they work.

As Paul said, make sure everything else is up to snuff before you adjust the carbs.

Here's a link with some more info.

http://www.teglerizer.com/sucarbs/index.html
Lee Fox

Im a fan of the hose trick also...But I had a cool simple idea last week on the hose trick

check this idea out...I think its a cool trick!

make 2 pieces of hose the exact same length (2 foot long) and duck tape one end of both hoses togather side by side about 6 inches from the end ... then stick the other ends of the 2 hoses into each carb throat and you can listen to both carbs at the same time by listening to both hoses at the duck taped end. thus taking the "Hiss Memory" out of play...

Thats where I have difficulty "Trying to remember what the sound sounded like that I just heard in the former carb.

So How cool a trick is that?? Im pretty sure I havent heard of it mentioned before. So this trick maybe a bad idea, as I find it hard to belive Im the 1st to have came up with this 2 pony trick of an idea...LOL

anyway Im hoping it works, I guess will find out this weekend.

Prop
Prop

sorry I forgot to mention... keep the 2 hoses parrel to each other with the same curves and lengths so the 2 hoses mirror each other.

Prop
Prop

On my 1500 I use a clear plastic tube about 12' long - 1/8th fill with water - connect each end to the bretaher outlet of a carb and then drape the tube off something high to form a U tube with the water about 1/2 way up each leg.
The carbs are balanced when the water level is even - it works at all revs if you use the right fluid - I tried various oils but they were all too thick so I ended up with water which works perfectly.
Total cost was about a shilling
Andrew Dunn

This thread was discussed between 07/07/2010 and 10/07/2010

MG Midget and Sprite Technical index

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