Hi all,

Whilst I have been playing with minis for about 8 years now, I've always left the tuning to an expert as I have never really been successful.

My car has developed a slight miss that only happens every now and then. Whilst trying to diagnose the problem, I noticed that the two spark plugs closest to the radiator are rather black/sooty indicating that the SU on that side has the mixture set too rich. Correct?

The other side (other two) has what I would call a greyish/brownish colour that too me looks right.

How do I go about leaning out the mixture on one side? Is it just a matter of winding the nut or do I need to undo the linkage? Please give me a guide to doing this.

Ryan

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Ryan Filippi
Minis In The Gong
[email protected]
www.minisinthegong.com.au

Wind the bottom nut anti-clockwise (looking down) to richen (I think) - try two "flats"at a time.

Cheers, Ian

You would need to wind the jet seat Anti-clock wise (looking from the top) to lean it out.
Start with two flats and go from there.
This the right SU feeding No1 and 2 cyl.
You do not have to undo the linkage.
Check your air filters are both clean as well.

Thanks guys,

This is what I had read, however other texts suggest undoing the linkages.

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Ryan Filippi
Minis In The Gong
[email protected]
www.minisinthegong.com.au

Well depending on what the idle does when you lean it out.
It may rise slightly. If it does get a bit of plastic hose, remove the air filters and listen to each intake.
The hiss/sucking should be equal. If they are not you will have to undo the linkage and balance the carbs.
I think this is right, havent done it in a while, havent looked back since i installed the 1"3/4 SU

scientific publications #64 has a good step-by-step explanation of how to synchronise the carbs

if it hasn't been done for a while, I'd undo the linkages and start from the start

this post from a long time ago is useful too

http://www.ausmini.com/forums/viewtopic.php?t=28695

http://www.youtube.com/watch?v=IfU47Oqq9wA
http://www.youtube.com/watch?v=IfU47Oqq9wA

these two vids might help you out, although the first one probably wont be too necassary considering yours are already on the car.

just note, these are hif, yours are hs2 or hs4, youll adjust the nut in flats rather than using a screwdriver to adjust your mixture. Just gives you an idea on what to look for.

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Aussie Leyland, Aussie Factory, Aussie Mini S.

Hi Ryan,

I have a Gunsen Colourtune if you want to borrow it. Its brilliant.

Basically it's a spark plug with a glass window which lets you view down into the cylinder and actually see the colour of the "flame" in the cylinder. Like a bunsen or a gas torch, yellow is rich, dark blue about right etc. Theres a colour chart and step by step instructions.

With the linkages you normally just loosen the parts on the shaft and then retighten them at the end so everything operates evenly when the throttle or choke is operated. Usually no need to disconnect throttle or choke cable.

Remember if you start turning/fiddling with the mixture nuts make sure you write down what you do to each so you can always go back to how it was. Usually you count the number of flats on the nuts.

It would be interesting to wind the mixture nuts all the way up (full lean) till they stop to see/count difference. Normally if you start from scratch I think they should be about 2 turns down at least as a starting point.

Also check that your damper pistons are moving freely. If you lift them with your finger (down the throat) there should be a little resistance (from the oil in the damper) and they should fall straight down with a dull metallic click. Do both feel the same?

It may be worth carefully removing the damper pots and the assembly with the needle and cleaning everything. (don't mix up left and right parts and carful not to bend the needles)

If one of the damper pistons is sticking and not lifting properly or if one is lifting too easily then that will effect mixture during acceleration.

Are the damper springs the same? Are the needles the same?

Check the choke is operating as it should. The first stage should only increase the idle speed, then further out a lever should pull the jets down ie the whole assembly where the mixture nut is.

also +1 on the post link gafmo provided, good info there.

Give me a yell if you want a hand or if you want to borrow the colour tune plug.

Phill

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68 Morris Cooper S Mk1 (*ex 78 1275 LS 4th last built, 70 Morris 1500 OHC & 70 MiniMatic)