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My Carbs Are Squelching

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Hi All,

I'm wondering if any of you have come across this before.

Firstly a little background. I recently purchased this outstandingly nice silver S3T which is pretty much perfect after a very close shave with an S3T at the extreme opposite end of the spectrum. There is one niggle which I put down to it not being used much recently or maybe old fuel or something. However, a few hundred miles later and it's not gone away.

The symptoms are similar to some of the current threads here, I get what seems to be a misfire particularly under load and very particularly when cool resulting in a juddering loss of power exacerbated by any boost. The problem is apparent at idle where initially from cold the revs sit at 500-600 then brief periods(1-2s) at around 800-900 where the engine sounds 'right', then back down to lower revs. Eventually as everything warms up the higher rev periods last longer and longer then at some point it sits happily at 800. Driving it after this point and everything feels fine - no misfires - though perhaps still some hesitation now and then.

I've checked every connection associated with the ignition and looking back at the history cap/rotor/leads/plugs are very recent, the coil looks a bit old and at some point I need to go round a freshen up some connections but nothing is obviously corroded/oxidised. The fuel pump whizzes away with just a mild change in pitch now and then.

I got a big clue today after starting it and leaning over the engine, I heard what can only be described as a periodic squelching noise from somewhere near the carbs, sounds very much like air being pushed/sucked through a small gap. As it warmed up the squelching gradually went away. At the moment I'm assuming that 'leak' is causing my misfires - Is this reasonable or a red herring?

I'd appreciate any thoughts you may have

Thanks

Ambrose

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Upgrade today to remove Google ads and support TLF.

Funnily enough I've just developed very similiar on mine. Alongside I'm down on power and backfiring on overun so I suspect a carb air leak.

One other thing though (I've eliminated this on mine thank you Pete G!) could be a sticking choke. With the engine running from cold, play with the choke mechanism at the carbs at the engine bay. If the squelching goes away it's a sticking or badly adjusted choke.


Regards

Mat

post-1-0302470001278592957.jpg

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I had a similar problem years ago, when boosting/under load, the power dropped off and it misfired. I had it tuned etc etc, but it never really cured it. The problem showed itself some months later when the wastegate jammed. After the wastegate was overhauled the problem vanished.

Just a thought.

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Mat,

I also have quite a bit of backfiring on overrun, but I'm not sure what level is 'normal'. I will have a fiddle with the choke assembly, I can remember pulling on the connecting bar then letting it go back to a kind of slack loose position, but Ill pay a bit more attention to it. Do you have the squelching sound too?

Chris,

Is there an easy way to tell if the wastegate is jammed, I assumed since it makes still makes those stuttery horse noises when I change gear enthusiastically it was OK. And did you have the squelchy nose too?

Looking back at the history the carbs and turbo are only about 3 yrs old and the wastegate diphragm was refurbished at the same time. Im wondering if it can be something as simple as the seal on the inlet manifold to the carbs. The manual is quite particular about the spacing at this joint. Im taking it to Gerald Turner on the 5th for a tune and general look over, hopefully he will solve it, and I will mention your experiences to him.

Thanks

Ambrose

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Ambrose,

I have just gone through my carbs. They are kind of tricky little mechanisims. I thought I would never get them worked out. First you need to balance them. The best method I found was proposed by Lee. Get some good vacuum gauges, and install a large fuel filter inline on the gauge hose. Remove the screws from the vacuum ports from the carbs. Hook the guages to the ports. Run the idle mixture screw in all the way, then out three turns, on each carb. Fire the car up and, using the balancing adjustments set the vacuum the same for both carbs. Once you have that set, put the vacuum screws back in. The carbs will more than likely cough. Adjust the idle mixture screws in until the coughing is intermittent. Remove the spark plug lead of each cylinder if the cough stops, hook it back up, and lean that cylinder until it stops. Now hook your gauges back up and make sure you still balanced. If not, balance them back out. If the carbs are the least bit dirty the will not run smooth.

I chased my tail all day with these carbs. Now they are smooth and run nice from idle to red line.

I am a Lotus novice and this is just my experience.

Cheers,

Clay

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Ambrose

Mine only started backfiring at the same time I got the noise. Don't think they should do this at all if set up correctly, but the Evil Dr may disagree! My gut instinct says inlet manifold leak. I've got a few days off this week so I'm going to have a go look see. I'll get back to you if I find the cause. Here's hoping it's simple!


Regards

Mat

post-1-0302470001278592957.jpg

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Mat,

Chris,

Is there an easy way to tell if the wastegate is jammed, I assumed since it makes still makes those stuttery horse noises when I change gear enthusiastically it was OK. And did you have the squelchy nose too?

No I dont think there is any checks that you can make. My car was'nt over boosting on the gauge. I had it checked and tuned by two different Lotus dealers, Norfolk Motor Company tuned it with the mercury tubes and they checked all electrical stuff etc, and could find no faults. It was only apparant when engine under load/boosting. If you go through all the "obvious" checks and it still does it then I reckon that it's worth taking the wastegate off and giving it a good clean out. It is an easy job to do apart from the nuts that hold it on to the manifold as they can rust in if they have'nt been removed before.

Regarding me having a "squelchy nose", I might have had a cold at the time!!! :thumbup:

No mate, no squelchy noise.

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Clay : It very much sounds like I should learn this procedure. Can you recommend some 'good' vacuum gauges, are they the same sort of things as in the 'carb-tune' thing and by fuel filter do you mean those little plastic inline ones or the big baked bean can sized things? Also how long do the carbs generally remain 'in tune' once set?

Mat : Yes, please let me know how you get on. If it is not raining when I get home , I shall try to pinpoint the squelch with a section of pipe connected to my ear canal. I'd love to think it is just 1/4 turn on one of those bolts....

Chris : Thanks for the extra info and Ill try it (or at least get Gerald too) if the normal things don't fix it. My nuts are still spotless and fabulously shiny.... ;)

Thanks

Ambrose

Edited by _ambrose_

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The guages I used were for vacuum and fuel pressure from General Tool. They have 3" dials on them and are easy to read. They need to be consistant. Each guage needs to read the same at the same vacuum. I used a vacuum pump with a guage to check them. You need a large bean can type of filter, otherwise the neddles will bounce. This was Lee's idea and it worked like a charm. First I tried a very sofisticated air flow meter, didn't even get close. I don't know about the "carb tune" devise. I have no idea how long it last. This is my first time to do it and it was about three weeks ago.

Cheers,

Clay

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Ambrose,

Can't say I noticed this problem when I owned the car.

I do remember that occaisionally the revs would drop but the car never stalled. I'd either catch the revs with the throttle or simple leave alone and after a few seconds the revs would rise again.

I remember after one NMEG meet last year, Nicksoldies was thrilled to see the flames shooting from the exhaust on over-run. It also made a lovely popping noise when driving through Chester.

I assumed there was just too much fuel in the mixture but I quite liked it so didn't bother with an urgent tune. Had I kept the car, I'd have had it looked at when it was being serviced.

Hope to see you and my old Giugiaro at Nick Whales place next month.

Graham.


Wing Commander Dibble DFC<br /><br />
North Midlands Esprit Group<br /><br />
NMEG "the formidable squadron"<br /><br />
"probably the most active Esprit group in the world" Andy Betts, Castle Combe May 2007

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I just used my new Carbtune pro and boy were my Dellortos out of wack. So was the position of the linkage screw between the carbs. My carbs were also acting like described.

What I fooud was that my rear carb had its bolts (holding it to the manifold) work loose enough to introduce an air leak that agravated the problem.

With the carbs properly secured, it took about 1/2 hour to run through the balancing process and match all 4 barrels.

While I don't have a Turbo, I do have the 45 Dellortos so I hope this helps. The Morgan Carbtune is worth the money even if you only use it once a year.

DomG


Dom Giangrasso

1977 S1 Esprit - Lagoon Blue

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Clay,

Glad to hear that the vacuum gauge/can idea works. It sounds like you took it one step further and used a set of four gauges.

What a fabulous idea, instead of moving from port to port!!!!!

Cheers, Lee

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Hello,

Thanks for your thoughts everyone.

I have still not managed to get outside and have a listen to it with my tube, but day off tomorrow so determined to get out there and poke about. From Dom's experience I massively suspect an air leak at the manifold. Had a look at the carbtune website and I'll definitely be buying one , I'm surprised at how cheap it is...Pity I cant just go to a shop tomorrow and buy one.

Graham, it never stalls just cycles from low to high revs. I must say I do rather like the noise too, went through a very posh clinically twee village on overrun, the frowns and disgusted looks from passers by when they turned to see the source were fantastic. And now the possibility of flames from the exhaust... fabulous. Look forward to meeting you and the sea of Esprits...

Ambrose

Edited by _ambrose_

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James,

Yes!

What a supremely nice bloke (Gerald Turner). He sorted out all the little squeals and whining from the brakes, the rattling under tray and had a good poke round underneath checking things.

My main concern : the misfiring, turned out that yes the carbs weren't balanced but more significantly the mixture was very very weak. He adjusted the mixture with the gas analyser and re-balanced the carbs. The engine sounds much better and backfire on over-run is reduced to a nice subdued pop and virtually no misfires when cold. The squelching is still there on startup but a few minutes of driving - then everything is fine. He also checked a whole bunch of other things first to do with fuel pressure.

Maybe most significantly of all he discovered that both my rear hub nuts were loose! (the wheels were wobbling all over the place) It would appear that the mating surfaces had been painted at one time which came off and left a good deal of play. He doubted the wheels would actually have come off but eventually the splines would have worn to the point of failure.

He also noticed that bottom rear links were bent (I suspect from axle stand misuse), my CV joints had quite a bit of play (though not serious) and some rubber was missing from some bit of suspension at the front. His general opinion about the car was very positive and he commented that all the recent work had been completed to a high standard. So I'm very happy indeed!

I highly recommend GT, he even put up with me asking dumb questions while he was working. Will certainly be taking the the car back to him for the next service (quite soon) and for all the little and not so little upgrades I want.

Ambrose

P.S. I also got to see a very very special silver one - quite magical !

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Fantastic news, Ambrose :thumbsup:

As you say, GT really is a top bloke and an all round good egg. Really knows and loves his Esprits too.

He's also a real perfectionist... so if he's impressed by a car it really does mean something.

James

Edited by Tentenths

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