Hi all (again)

So I have never ever attempted to adjust my twin 1 1/2's in any way but it seems I may have to if I want to save any money instead of taking it to a mechanic.

So as the title suggests - I need to adjust my idle, idle up to be exact. My carbies recently got tuned and the car runs absolutely perfect when accelerating/decelerating but then at traffic lights and the likes it idles dangerously low (around 500rpm) and sometimes completely stalls out. The carbies then was made leaner by one flat and it made it develop a misfire accelerating in the low RPM range but it idled better when stopped.

So I got it changed back and it's idling really really rough and low again but runs fine while driving. Is there a way I can raise the idle to around 1000rpm without changing the actual mixtures?

I'm sorry if this sounds really basic, I've just never attempted any tuning of any sort. Is this something I could do myself or is it too complex?

Many thanks
James

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I wish I had some sort of witty quote in my signature

THis is the best image I can find, but it gives a good indication:


What is referred to in this image as the "Throttle stop screw" is your idle screw. If you pull your accelerator cable, this screw determines how far back it can go when it returns, so if you wind it in it won't close as far, and your revs will rise. On an HS4 it is slightly recessed next to the dashpot like in this image. You will need a screwdriver.

I can't comment on how this will differ for twins though - I've never had to deal with them!

As the above, just adjust your throttle stop. As long as you adjust both carbs by the same amount you'll be fine. This will only change the carbs at idle, or when coasting in gear. You should be able do this while the engine is running and check on your rev counter (if you have one), but push the pedal in and let it return by itself to get a good idea of how the idle has changed.

If you change the mixture, it changes for all throttle conditions, and it can throw out your tune.

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Twins!

Once you have sorted out the idle adjust screws on both, then you need a meter or so of 1/2" heater hose.
You put the heater hose to your ear, and then the other end in the mouth of the carb at about the same position for each. If one sounds higher than the other, then it needs to be closed a little, or the other needs to be opened a little.

Very small changes in each carb adjustment make big changes in sound, so it is very effective. I prefer this over the expensive carb air flow meters

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Could you make and use something like this to balance twins on a mini?
https://www.youtube.com/watch?v=7D_f05_a74Y

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1975 Hairy Lime/White Clubby
Build Thread: http://www.ausmini.com/forums/viewtopic.php?f=3&t=80657

Thanks for your replies everyone

I just went out and inspected my carbs. Is this the correct screw I need to turn?

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I wish I had some sort of witty quote in my signature

Yes that is the idle speed adjustment.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Important. In your photo there is also a screw just to the left of idle screw that points toward a cam. (no 3 in the diagram) Double check that your choke is right in and that while you adjust the idle there is a gap between the end of that screw and the cam that it points too.

Then after you have adjusted your idle make sure there is still a small gap there. Probably won't be an issue for you in this case because you are increasing the idle and so that gap will increase, but basically when everything is set and the choke is right in there should always be a small gap there.

When you begin to pull out your choke that cam rotates, pushes the screw and therefore increases the idle with choke. Watch while someone pulls the choke out and you will understand how it works. Also check that when the choke is pulled slowly out that you can see both carbs throttles open approx same time/amount

The method with the tube Mick suggests is the way my Dad taught me and I've also found it the best method for balancing.

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

Thank you Phill, I made sure there was the gap so should be all sweet now.



Thanks Mick

What is meant by the 'mouth' of the carb exactly? Doesn't seem to be anywhere I can stick a hose in haha

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I wish I had some sort of witty quote in my signature

You need to put the hose into the mouth of the carb, the inlet.

It doesn't matter where specifically you hold the hose on each carb, just that the relative area is much the same on each.

Give it a try and you will see.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Mick is saying to remove the air cleaner filters and place the tube at the entrance to the carby elbow (i.e. where the air is being sucked into the carby itself). It's the noise of the moving air you are listening to.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

Thanks guys I understand. I got a good adjustment of the idle today and will fine tune each carb with a hose tomorrow.


Just another quick question. When the mini is started up (even when engine is already warmed up) the engine won't hold it's RPM. It sits at 1000rpm and then it begins to drop and it sort of splutter and the rev counter jerks a bit. The engine will then drive great but until it's gone a few km's it will have a little misfire on idle. Once it's done a few k's it's more or less fine.

Is this just a common thing? not holding it's idle great until it's done a few km's? or do I need to look at a fix?

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I wish I had some sort of witty quote in my signature

Maybe still a bit rich and fouling the plugs?

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http://www.youtube.com/user/Hanras

I agree - if it's running a bit rich, it can misfire rhythmically and/or hunt for an idle speed.I changed the jet on my carb not long ago and put one that was too big in - it would drop to 400rpm and then rev up to 2000rpm and just jump between the two.

If after a few km everything is good and is holding idle ok I would say that's normal. I find it takes a 3 or 4 km for the engine to be completly warmed up and to get a normal speed idle. Your temp guage may show normal but that is usually only the water temp. You can tell from the oil pressure. It is quite a while before the oil warms right up and pressure at idle drops right down.

Remember that the first half of the choke (on an su) is really only idle speed adjustment so just keep it out as long as is necessary until it idles ok with it in.

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