Lotus Elan

Xeber concern

PostPost by: diablo » Sat May 26, 2018 7:04 am

I have a problem with one of the 2 Weber ( Elan S4 ) . On one ( A ) , it react when I move the richness screw ; the engine speed moves up or down when i screw or unscrew the richness ; the exhaust headers corresponding are hot ( 200 deg ) . The second one ( B ) does not react to the screw moving ; the exhaust headers corresponding are cold ( 60 deg ) . I am quite sure it is a carb concern because when I change the place of the carbs ; A in place of B and vice versa , the fault follows the carb ; A is always OK , B always wrong . I have clean them ( ultrasonic ) 2 or 3 times so I think they are clean now . The tuning is : Main jet :115 , Air corrector jet : 220 ,slow running jet :50F8 .
After a complete rebuild of my car, I try to solve this concern since one year now and I have not yet drive it !
Thanks for your help
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PostPost by: nmauduit » Sat May 26, 2018 8:13 am

Bonjour,

the idle richness circuit uses the idle jet and fuel passageways : did you make sure nothing blocks there by blowing air and seeing the spray through?

weberb.gif and
weber idle circuit
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PostPost by: vincereynard » Sat May 26, 2018 11:25 am

Does it start firing when the throttle is opened above idle (2000 +)? Do you have a colourtune plug?
I found it very useful as you can just see the point when the cylinder starts to react.

Is there any possibility it is the same problem as I had ? No1 butterfly was not in opening the same as No2.
lotus-carbs-f40/dellorto-tick-over-system-t42021.html

"nmauduit" - That's a useful diagram. Do you have a similar for the whole carb and / or Dellorto?
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PostPost by: nmauduit » Sat May 26, 2018 2:25 pm

vincereynard wrote:"nmauduit" - That's a useful diagram. Do you have a similar for the whole carb and / or Dellorto?


I've seen the Weber technical drawing in many places, they were on period technical documentation, possibly then colorised

for example online

http://www.veloceregister.net/weber.htm
http://www.teglerizer.com/dcoe/rasorcom.htm

For Dellorto some digging may be required, they mostly do motorcycle carbs these days it seems http://dellorto.it/en/products/carburetors/ though a search with DHLA and "idle circuit" pointed to a Laverda club site with similar drawings (there must be some documentation out there)

http://www.or600.laverda-club.com/conte ... ent_e.html
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PostPost by: Esprit2 » Sat May 26, 2018 7:18 pm

Diablo,

The first step to tuning the carbs is always a thorough ignition tune-up. Then set the floats to 8.5mm Height and 15mm Droop (for brass floats). If you haven't done those steps yet, then it's a waste of effort to talk about other possibilities.

Have you balanced the carbs? Anytime you remove & replace the carbs, the chances of them ending up balanced on their own is nil. No, they won't hold their old settings, and yes you do have to take specific steps to re-balance them. The symptoms you describe are typical of carbs that are out of balance (at idle, one works and the other doesn't). So, have you balanced them? If not, then DO IT, or pay someone who knows how to do it.

Varnish deposits from old gas can be hard, like plaster. If you simply put the jets in an ultrasonic cleaner, then you end up with clean varnish in the jets... but they're still plugged. The amount of varnish build-up in the jets required to make a difference is so small that you may not notice it with a naked eye, so use a magnifying glass. "Plugged" is obvious. But even if you can see through the jet, can you also see any deposits on the orifice wall? Clean them to bare metal, or they're not clean.

Manually clean the jets, using a small wire (preferrably soft copper to avoid scraping the orifice). Passively cleaning by putting them in an ultrasonic cleaner, squirting them with aerosol carb cleaner, or blasting them with compressed air may not do anything to remove varnish. So, have you 'really' cleaned the jets?

Which version of the engine, and which camshaft does it have? Carb jetting doesn't work 'alone', and it's influenced by the camshaft and compression ratio being used. No body can guess at how appropriate your carb's current jetting is without knowing more about the engine. But with the info you've provided so far, it appears the Main Jets are correct, but the Main Air Corrector is a few sizes too lean at 220 (bigger = more air = leaner). The Idle Jet and Idle Air Corrector are standard.

Weber DCOE Jetting for the Lotus Twin Cam
*** (40DCOE-18 early / 40DCOE-31 later)
Model ....................... Standard ... S/E ............. Super S/E, Sprint, Big Valve
Camshaft ................. B-Cam ........ C-Cam ....... D-Cam
Choke (mm) ............ 30 ................ 32 .............. 33
Main Jet ................... 115 .............. 115 ............ 120
Air Corrector .......... 200 .............. 150 ............. 155
Slow Running ......... 50F8 ............ 50F8 ........... 50F8
Acc-Pump Jet .......... 40 ................ 40 ............... 35
Acc-Pump Stroke ... 10mm ......... 10mm ........ 10mm
Starter Air jet .......... 100 ............. 100 .............. 100
Starter Fuel jet ........ F.5/100 ....... F.5/100 ....... F.5/100
Emulsion Tube ........ F11 ............. F11 .............. F11
Needle Valve ........... 1.75 ............ 1.75 ............. 1,75
Float Levels ............. 8.5mm Height and 15mm Droop (metal floats)

50F8 is the combined Idle Jet (50), and the Idle Air Corrector (F8). The Idle Circuit feeds the engine up to 4000 rpm, then hands off to the Main Circuit. When you get the engine running, do the following tests to evaluate the Idle jets:

Start the engine and let it run until it's fully warmed up. With the carbs balanced and the Idle Mixture Screws adjusted for peak manifold vacuum (or peak idle rpm), adjust the Idle Speed to the lowest rpm possible consistent with smooth running.

With the engine at normal idle speed, open the throttle slowly enough that the Accelerator Pump isn't much of a factor (not 'dead' slow, but don't snap it open). If the engine hesitates just off-idle, then the Idle Air Corrector (F8) is too lean. Go a step or two richer (smaller size number = less air = richer) until the hesitation just goes away. When satisfied, set the Idle Speed back up to a normal 900-1000 rpm.

Take the car for a drive on a road that has little traffic, and make a full throttle acceleration run in an intermediate gear... 2nd or 3rd (you'll rip through 1st too quickly to be helpful, and 4th will just get you a speeding ticket). If the engine stumbles approaching 4000 rpm, then the Idle Jet is too lean. Go richer until the stumble 'just' disappears, no further. If the engine doesn't stumble on the first run, then you can't be certain if the Idle Jet is correct, or too rich. So go leaner until a stumble just becomes apparent, then go back a step richer until the stumble just disappears.

The Idle Jet and Idle Air Corrector affect one another. So if you do end up having to make a change to the Idle Jet, then go back and re-check the Idle Air Corrector once again. Adjust the Idle Air Corrector for off-idle hesitation, and the Idle Jet for a full throttle stumble at around 4000 rpm.

Any time you make a jetting change, go pack and re-adjust the Idle Mixture Screws. In carbs, everything affects everything else. A carb is like a spider web... touch it here, and it vibrates over there. So during the tuning process, you will end up re-doing many adjustments over and over again. That's normal, it's the way carbs are, so just do it.

Having written all of that, if I were there, I'd START by cleaning all the jets. Then adjust the Idle Mixture Screws, accurately balance the carbs, then re-adjust the Idle Mixture Screws, followed by setting the Idle Speed. All that would just get us to a good baseline setting from which to evaluate the idle circuit's jetting. And if any jets do get changed, then go back and re-adjust the Mixture Screws once again.

Good luck,
Tim Engel
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PostPost by: webbslinger » Sat May 26, 2018 8:10 pm

Do you have the fine tapered brass idle screws or the steel ones? The tips break off of the brass ones VERY easily and can lodge in the hole. That or something else blocking the idle circuit may be the problem.
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PostPost by: diablo » Mon May 28, 2018 8:13 am

Hi you all
Thank you very much for your answers ; I read them very carefully ans I am afraid I have to answer .......I did it .
The idle screws are in steel . I carefully clean the jets , not only by ultrasonic way but I blowed them and I have gauges and tool to rimm them so I am sure they are clean . I have also a weber tool for the balancing , but difficult to balance with one of the carbs not working OK . After the multiple mounting and demounting the carbs , I use a trick to get a beginning of balance , I put a thin wire in the first progressive hole of each carb , and put the butterflies
of each carbs at the same position , using the wires as a gauge . It is good as a roughly beginning for balance .
The ignition is OK , I checked it several times . What make me crazy is that the defect follow the same carb , and this carb looks the same as thegood one ! I have got the opportunity to compare them during the numerous dismantling I did . Perhaps I should investigate in the starter area ; I think if it does not close fully , fuel could pass this way . Concerning a road test , I confess I am not courageous enough to do it untill I have not made progress to solve this problem .
I know how the weber works , I had some Ferrari ( i still own a Daytona) and this Elan makes me crazy with this weber !
I bought another pair ( not the same modell ) and it did not work at all .
My car is coming from the states , it is standard , and the carbs are the original one .
Cheers
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PostPost by: Orsom Weels » Mon May 28, 2018 8:37 am

Hi diablo, I can sympathise with your pain, I went through much the same after I put my +2 back on the road after a few years in storage. I could not get one barrel of one carb to run properly at anything under about 2500 rpm. I had them ultrasonically cleaned three times by three different people, poked & prodded, soaked them in all sorts of solvents, blew them through, swapped jets around & would have sworn that everything was perfectly clear, but the problem always remained on the same barrel of the same carb body. Eventually I gave in & fitted a brand new set of 151's & the car was transformed, nice smooth idle, no flat spots, good performance & best of all, much improved fuel economy, far better than it had ever been. There must be a fuel/air passage that is blocked or partially restricted, but I was damned if I could find it & no one else has been able to either.

Regards, Tim
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PostPost by: nmauduit » Mon May 28, 2018 8:43 am

diablo wrote:I have also a weber tool for the balancing , but difficult to balance with one of the carbs not working OK . After the multiple mounting and demounting the carbs , I use a trick to get a beginning of balance , I put a thin wire in the first progressive hole of each carb , and put the butterflies
of each carbs at the same position , using the wires as a gauge . It is good as a roughly beginning for balance .

I bought another pair ( not the same modell ) and it did not work at all .


I understand there is only one cylinder not "giving" as we say here, without proper combustion resulting in one header out of 4 staying cold, correct ? (if 2 cylinders were not running getting the engine to operate would be very difficult)

I suppose that over your various dismantling you also checked that throttle operation was smooth, and butterflies were centered, closing well and moved in good synchronicity.

As for en enriching circuit causing a disbalance, if there was a leak of fuel you would hear it (pops/bangs) or see it (black soot) eventually, so I'm tempted to rule that out

So then to balancing - or leak searching : how fast do you run the engine when you do so? is it an idle problem that goes away when you run faster (say 3000-4000) ? are the spark plug condition indicative of something on one cylinder, and have you performed an air leak search? Also, depending on the actual carb version, did you check if one venturi could be rotating ?

I'm also puzzled by the not working at all of the other carbs : what type (number) were they, and were they jetted with the initial set ? I have a set of 31s here for my next build, though not tested yet since cleaned and checked, in case you get too frustrated...
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PostPost by: vincereynard » Mon May 28, 2018 9:38 am

Orsom Weels wrote: Eventually I gave in & fitted a brand new set of 151's & the car was transformed, nice smooth idle, no flat spots, good performance & best of all, much improved fuel economy, far better than it had ever been. There must be a fuel/air passage that is blocked or partially restricted, but I was damned if I could find it & no one else has been able to either.

Regards, Tim


I would be tempted to follow Tim's advice. Give up and fit a new pair of properly jetted Webers or Dellortos (as long as they have a balance circuit). The frustration is not worth the angst of continuing with the same
result. Check for mechanical air leaks at the usual places and you should be good to go.

Good Luck.
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PostPost by: JonB » Mon May 28, 2018 3:08 pm

nmauduit wrote:http://www.or600.laverda-club.com/content/tips/carbs/dhla/content_e.html


Great link, thanks nmauduit! I have bookmarked it.
1973 Elan Plus 2S 130/5 - UK - Chassis 50/1115L
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PostPost by: bill308 » Sat Jun 02, 2018 1:10 am

Old carbs are simply not worth the effort IMHO. Go with a new set of Spanish made Webers and jet as required. No vacuum leaks, fuel leaks, corrosion, bent/cross threaded mixture screws, air leaks at the throttle shaft, twisted throttle shafts, blockages in the fuel passages, corrosion, etc. New 151's have intercarb, air balance circuits, so if the throttle shaft twists over time, one can compensate for it. The other thing the new carbs offer is the ability to screw in vacuum taps. This allows the use of a manometer/gauge to measure vacuum for balancing purposes. Finally, new carbs look better.

The next thing to do is install a O2 sensor bung in the exhaust manifold collector and get yourself an A/F meter that will record combustion data, over the road, for later analysis. If you are serious, do it right, or take it to someone who will do it right.

I edited this post to add a couple of additional faults and remove the G suffix from the 151 model number. The G (German version) only applies to the 45DCOE152G as far as I know, a variant that has 5-progression holes for better low speed tuning flexibility.

Bill
Last edited by bill308 on Thu Jun 07, 2018 4:08 pm, edited 2 times in total.
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PostPost by: diablo » Wed Jun 06, 2018 7:40 am

Hi you all
One more time I took off this bloody carb . I watched it carefully ( one more time!!!!) and found that when the butterflies are fully closed , the first of the progressive hole stay open a little bit . Can this explain why the idle srew is inactive ? My next step will be to investigate why it does not close , and ONE MORE TIME , put the carb back on the car and pray God , Allah , Vichnou , Ste Rita , Mr Bean.......
As I told previously , I have another pair of carbs 143 should they work ?
Cheers
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PostPost by: nmauduit » Wed Jun 06, 2018 10:43 am

diablo wrote:Hi you all
One more time I took off this bloody carb . I watched it carefully ( one more time!!!!) and found that when the butterflies are fully closed , the first of the progressive hole stay open a little bit . Can this explain why the idle srew is inactive ? My next step will be to investigate why it does not close , and ONE MORE TIME , put the carb back on the car and pray God , Allah , Vichnou , Ste Rita , Mr Bean.......
As I told previously , I have another pair of carbs 143 should they work ?
Cheers
Diablo


unless progression holes have been redrilled and one of them was not drilled at the same location as the others, this would indicate that one butterfly might be twisted with respect of the other (is it a steel shaft?) - this kind of issue should be visible with an air flow check like a synchrometer

Image

at least it may not be a richness issue as initially pursued, you may want to set your butterfly closing as perfectly as possible and as simultaneously as possible before the next attempt (if you try to twist them back into a more parallel position, make sure you protect them well so as to twist only the shaft, and don't overdo it).

good luck !
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PostPost by: NickD » Thu Jun 07, 2018 12:25 am

Diablo,

Is the 1st progression hole covered on the A carb when the throttle is closed?
If so, (and assuming that progression holes inthe A & B bodies are in the same places), have you checked that the throttle plates are the same in the A & B carbs?
The throttle plates for the 40DCOE are available in 78 degree and 79.5 degree versions, and the 78 degree version will uncover more of the first progression hole. If your A carb has 79.5 degree plates and the B has 78 degree, then this could explain the uncovered progression hole. The angles are usually stamped on the face of the plates.
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