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simonf

Carburettor Jet Cleaning

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Had a friend with an excel that had partially gummed up idle jets, ran fine on idle on choke when cold but stalled when the choke was in. He resorted to poking some thin wire down them to clear them out, probably not the best way but has worked fine since.

Took a while to find as on removal could blow them ok so had assumed they were clear.

 

 

See my post #3 on this thread....modern petrols leave 'orrible deposits behind!!


Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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Jets look fine to me... I took the cover off and pulled each brass fitting out, I've no idea which is the idle and which the main jets (guessing the giant long ones are the mains!) but they were uniformly clean, not blocked or visibly gummed up.  Clearly not a float bowl issue as once off idle they all fire well. 

 

I've got the lumenition system... but I can't think of anything that would affect just 3 and 4 which keeps bringing me back to the carb...

there was mention of an air leak being possible, as previously discussed I've re set the gap on the inlet manifold to 1mm, could there be air being sucked in there?  If I stuck a tube in my ear and held the other end near the inlet manifold do you think I'd hear it if it was sucking in extra air?  the suction would drop once the butterflies are opened which might explain running OK when off idle. 

 

More stuffing around tomorrow, maybe it'll come good like the car in this original thread!

Cheers,

Simon

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Hi, I have just found the easiest explanation yet of the mysterious wonders of our carbs and a nice clear statement on how to set them. Ignor the first couple of pages unless you want to re-ject your carbs but the rest makes simple reading.

 

http://www.s262612653.websitehome.co.uk/DVAndrews/dellorto.htm

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Mr Mole you beat me to it! Is there any issue you have not had to fix? We almost need a wiki if faults and fixes.

Edited by Wilf

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I have just been through something similar over the past couple of weeks on my S2, I rebuilt my carbs after putting them in an ultra sonic bath, all original jets but a complete overhaul kit installed.

When I first ran the car up two of the cylinders were spitting back, I adjusted my timing advance and balanced the air flow on the butterflies. On installing the Vacuum gauges it was clear cylinder 2 and 3 were running very poor and I could get no adjustment.

On removing the plugs 1 and 4 were the perfect light tan where 2 and 3 were black and dry looking.

I then decided to put the main, idle and starter jets back in the bath for several hours, one of the idle jet holders was distorted like it had been pulled down on something so I replaced it.

Once fitted back all seemed to improve greatly, I have the carbs to a stage where I am 80% happy, I will need to revisit as my manifold gasket is leaking slightly and I have not set my CO level yet only set for best performance.

Worth inspecting your jet holders and cleaning the plugs, I would certainly go for another jet clean too. This is the first time I have really struggled after a carb build so learnt a few lessons. I set my accelerator pumps up as well before installing on the car, it now revs very well and as stated above 3000 rpm where the main jets work I never had issues.

Good luck and keep us informed on progress.

Dave:)


Do or do not, there is no try! 

 

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Mr Mole you beat me to it! Is there any issue you have not had to fix? We almost need a wiki if faults and fixes.

 

Probably not, by now....26 years of greasy fingernails does tend to be pretty all-encompassing. When I bought the beast it was because I wanted something I could play with; all the trials and tribulations have to be viewed as "fun"....an unending series of interesting little problems, needing creative thought to solve. All the hassle becomes as nothing when it's a nice sunny day and she's running well, and you drive somewhere for a swift half and just sit there looking at her....as does everyone else! Far more satisfying than simply spending money..... 

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Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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Just wondering- would Carb Cleaner be suitable for cleaning jets?

Or is that too obvious?

 

You have deduced the obvious.  :)


Tony K. :)

 

Esprit S1s #355H & 454H

Esprit S2.2  #324J

1991 Esprit SE

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So after a day spent on and off working on the car. 

 

Took all the jets out, found various thicknesses of wire/bristle to put through.  There was a small build up visible on a couple of the holes... carefully cleaned up, washed thoroughly with carb cleaner (which should break down the deposits too), then reassembled. 

 

No change at all.

 

So I swapped the jets from carb to carb, and the problem didn't move with the jets.  Ergo it's not the jets, or not only the jets. 

 

Inspected then swapped plugs, again problem didn't move. 

 

Took the carbs back off, checked the O rings and rubber isolaters, carefully reassembled.  No change.  Tried various different tensions on the mounts, no change. 

 

Checked spark to 3 and 4.  Spark may be weaker on these two than on cylinders one and two. Took off and inspected the distributor cap.  No discernable difference between all four contacts.  Apart from the gap between the rotor and the contacts on the inside of the cap, is there any part of this system that could affect two cylinders only?  Cleaned the cap thoroughly and reassembled.

 

I looked at the cap and as far as I can see there's only one way to fit it.  I'd love to rotate it 180 degrees and see if 3 and 4 then fire!

 

Checked idle mixture, all carbs are 3.5 turns out from fully in.  Tried a couple of different mixtures on the rear carb, no change.  Put it back at 3.5 turns out. 

 

Sings like a bird off idle, and runs on two cylinders at idle. 

 

I'm a bit stumped!

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Simon

My next step would be to confirm fuel pressure to the carbs from the SU pump, check the filters fitted around the banjo pumps too. I think at this stage I would whip the carb off and give it an overhaul as something's not right with the idle circuit, I have had part of the lead port filling plugs block a carb before although very rare so hopefully not the case. What colour were your plugs when you removed them?

Have the carbs been balanced, I am surprised you can even get it to idle if only running on two cylinders, does it get worse when you pull the HT lead off on one of the poor cylinders when running?

Might be worth doing a compression test when hot to confirm all is healthy within the engine and your valve clearances haven't closed up allowing a valve to remain slightly open.

All guess work at this stage though as sounds odd, have you got play in the dizzy shaft? Check HT leads and plug clearances too.

Sorry for no direct answer

Dave :)


Do or do not, there is no try! 

 

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Simon, have you set the carbs to be balanced for air? If the air vacuum isn't even across the carbs it could mean a complete carb (so 3&4) don't get enough air& fuel when on idle, no matter what you do to the mixture it wouldn't run well.

 

As a simple, and rough, test, simple apply a tiny amount of throttle to tell whether those two start firing at that level.

f they do then fire, with the engine off, slacken one of the screws that secures the linkage of the two carbs, adjust the opposite screw (they sandwich the plate of the other carb), adjust it so that the missing carb has a screw-turn worth of throttle, and secure with the other screw.

From memory, carb for 3&4 has the cable attached, so it's the screw that's on the cylinder head side to slacken by one turn, and the screw that's on the air filter side to screw in one turn.

 

Then try running.

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Has anyone mentioned "O" rings in this thread. Waste of time trying to balance carbs without checking these, and they're so cheap just bung a new set in.


Life is like a sewer, what you get out of it, depends on what you put into it. (Tom Leahrer)

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Simon has considered the air leak in post #5 in another topic, but replacing them is a good idea.

http://www.thelotusforums.com/forums/topic/64331-fast-uncontrolled-idle/

 

On that topic, anybody know the size of the O rings? I'm thinking 51mm Inside diameter 4mm thickness, anybody have any to measure?

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Thanks folks for suggestions

 

Carbs are balanced by eye, all butterflies closing fully and at the same time

 

I cracked the banjo on the questionable carb and fuel sprayed out so fuel delivery is good, engine runs well off idle too

 

HT leads are new, gap on all plugs checked, swap plugs and they will run in cylinders 1 or 2 but not in 3 or 4

 

O rings are used but in good nick, nice and fat and no cracks so I'd be surprised if they were the issue... off idle there's no problem, if they were leaking air would this be the case?

 

Plugs in 3 and 4 are wet after running the motor suggesting a fuel air mix of sorts is getting to the rear cylinders.  I haven't sniffed it, just assumed it's petrol.  Could check this tomorrow.  Even if there was some 'other' liquid in the carb it wouldn't run well off idle (being revved) and it does. 

 

Cylinder 3 and 4 'non running' state identified by pulling plug leads... engine will run on one cylinder!  Only just but didn't die immediately.  That was with 4 off, no change, then 3 off as well, no change, then two off and a noticeable change. 

 

I'm still thinking spark, tomorrow I'll take the cap off again and give all the terminals a little rub with wet and dry, ditto the end of the rotor arm. 

 

I'd be interested in a size for new O rings, parts manual doesn't specify.  As mentioned above SJ has them for 35p each!  I'd be impatient waiting to get them from the UK... and the postage is £15...

 

Battle again tomorrow. 

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Get  piece of rubber tube, and go back to the pre-carb-balancing-gizmo stone age. Run the engine at a fast idle, so that all the cylinders are working. Stick one end of the tube in your ear and the other in each of the chokes in turn...you should hear the same level of hiss from each one. Slowly lower the idle speed until 3&4 cut out.... If 3&4 aren't giving you a hiss, then the butterflies are shut..... In fact, you should be able to detect a difference straight away as soon as you listen....1&2 sound like they are further open than 3&4, so when you lower the idle speed you get to the point where 1&2 still work, but 3&4 are now proper shut and thus the cylinders won't fire. The cure is to make 1&2 shut off fully, with 3&4, then adjust the main idle screw so that all 4, opening together, give you a good idle. I can't see this being ignition.... but if it turns out to be sparks, please tell us exactly what it was!! (I usually work on the theory that the more you think it's carburettion, the more it turns out to be sparks....) 

 

Before gauges, that's how we used to balance multiple carburetter setups....you can be very precise with practise; young Moley had many happy hours tuning his MG TC twin SUs.....before he supercharged it and went to a single (large!) carb....


Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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Thanks folks for suggestions

 

Carbs are balanced by eye, all butterflies closing fully and at the same time

Battle again tomorrow. 

With the Dellortos, the idle bypassed the butterflies, so balancing idle is sort of irrespective of those.

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With the Dellortos, the idle bypassed the butterflies, so balancing idle is sort of irrespective of those.

 

 

So does this counter the 'rubber hose in ear' suggestion? 

 

I cleaned the cap contacts and no change. 

 

I'm going to run it for a while at higher revs and try to confirm that the rear two really are firing.  I've assumed that they are when off idle as all lumpiness reduces quite dramatically. 

 

I'll set it at the revs where I reckon they're all running then go around pulling leads again to see what happens. 

 

I have just fitted a new cambelt, could I have a gross timing error giving these symptoms?  All timing marks looked good and I've given it a dynamic time, now set around 7 degrees btdc.  I assume if two cylinders are happy then all should be?

 

Cheers,

Simon

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The tube to ear method may still work but it would rely on the hiss coming from the idle tubes and I doubt that's going to be loud enough. In fact. Borrow/ purchase a 4 cylinder carb balancer if you can, they aren't too expensive.

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I would run more than 7 degrees advance, my car runs best at 13 degrees BTDC with 26 BTDC at 2400 revs. You can set this by ear quite well by carefully turning the distributor while running until the idle stops increasing then just back it off slightly. Keep forward pressure on though as you don't want the dizzy to disengage. I normally check with an advance timing light after and it is spot on, you will need to check the CO though as you can easily tune for best running not emissions. Worth rechecking your timing belt tension if you have changed the belt and since run it as they often need resetting when settled.

If you don't have one it is worth getting a Morgan Carbtune for setting the carbs as not expensive and pretty effective.

Good luck today sorting it out

Dave :)


Do or do not, there is no try! 

 

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The air going into the engine comes through the choke tubes. These contain the butterflies...if you listen to the airflow going into each choke in turn, you will hear if you have a carb with the butterflies open or closed. You aren't trying to listen to slow running jets/system...in any event, even at idle, the butterflies do not seal the choke tubes....you try running the engine with the butterflies actually shut and see how you get on...(!)  Adjusting the idle speed requires the butterflies to be adjusted...that's how the idle speed is set....in conjunction with the mixture and air bleed screws.  Stick a bit of rubber hose in your ear and have a listen....I've set up twin Weber and Del'Orto carbs with nothing else than that, before now, and got a rock steady idle....balanced a threepenny bit on the cam cover.....

Morgan Carbtunes are wondrous things, I have the early version with the mercury gauges (!) and they really make the setting up job much easier. But a length of rubber pipe and the Mk1 Ear'ole does very well...certainly enough to compare 1&2 with 3&4!!

With timing, setting it for the best idle may well not give the correct conditions at full power. Hence the timing light.... All engines will vary and the optimum timing will, too, but simply setting it idle may not be correct. The engine on my boat is older than God's dog...I set the timing on that by running under load at around 6 knots and twiddling the distributor until it sounds happiest!! Easy enough on a boat with someone else steering...not so simple in an Esprit...(!)


Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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At idle the butterflies are closed and the air enters the carbs via a different inlet.

 

Afraid not, take a look at the diagram, the arrows show the airflow.

 

dhlaoperation3.gif

Idling

Fuel from the float chamber is metered through the idle jets (20) and mixes with air from the well (3) through the channels (19). Mixture through channels (21) reaches the idle mixture screws (22) and, when regulated by them, reaches the main barrels (10) downstream of the throttles (13).


Cheers,

John W

http://jonwatkins.co.uk

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 I don't agree.

 

When overhauling the carbs, the butterflies should be able to close completely when at rest, otherwise the idle can not be set accurate.

However, Ones the carbs are mounted and coupled, the two carbs must be balanced to one another by the coupler screw between the two.

Now, the rear carb has the idle speed adjustment screw, and it's butterfly opening at idle is controlled by that screw. The front carb is held open by the linkage via the coupler screw ( that enables balancing it to the rear carb.).So the butterfly opening of the front carb is matched to the rear carb by that coupler screw.

The bleed screws are only used to match the vacuum between the two barrels of the same carb. One should be closed, and only the strongest barrel should be opened to match the weaker on each carb.

 

So ones balanced the idle ( 900-1000rpm) is set by opening the four butterflies a bit with the idle speed adjustment screw on the rear carb.

 

Of course , we are discussing the dellorto dhla carbs here.

 

Geert

Edited by gvy

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Hi Geert, out of the hundreds of threads on this topic this is the best and simplest exlanation I have heard yet.

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