Lotus Elan

Do weber 40 dcoe,s need a choke ?

PostPost by: elanner » Wed Jul 02, 2014 1:57 pm

Tim and Rohan,

Thanks - those are very interesting replies. The concept of a sucking vacuum compared to a venturi generated vacuum never occurred to me. Neither had the benefits of the downhill design of the Twin Cam inlet manifold. And letting a few accelerator pump shots evaporate for a bit while putting on the seat belt and other stuff is a neat idea.

I knew there was a good reason why I'd never opened my Weber manual before. A little knowledge is so dangerous! ;-)

My engine has always started very well, but I've definitely had occasions where the sometimes lengthy cranking needed to fill the carbs after a period of non-use is countered by a sudden worry that I've flooded it. No petrol or too much petrol, that is the question! I guess I should install an electric pump or primer bulb.

Again, many thanks.

Nick
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PostPost by: Esprit2 » Wed Jul 02, 2014 2:45 pm

elanner wrote:I knew there was a good reason why I'd never opened my Weber manual before. A little knowledge is so dangerous! ;-)
Nick,
Do read the manual(s). The problem is that most manuals are written assuming the reader has some prior knowledge of what's going on, and just cover the information that's specific to the carb model being discussed. Haynes manuals are generally geared for the amateur who may need more complete information, but I don't know that Haynes are always the most in depth on the other end of the scale either.

The best entry level book on Webers and Dellortos is Des Hammills, "How to Build & Power Tune Weber & Dellorto DCOE & DHLA Carburetors". It's not the most technical, but it covers topics from a pretty basic starting point, and then illustrates assembly with a lot of photos rather than line-drawing illustrations. You see your real world parts on the page.

It's a good basic manual/primer, but don't take it as gospel... there are some weak bits, if not plain old errors. For instance, Des gives the Dellorto float height as 15mm, ignoring the fact that there are three different float weights available, each requiring a different float height. And Lotus ignores the Dellorto specs, tweaking the float height a bit in tuning the carbs for their own engines. 15 mm is not a one size fits all solution.

There's a lot of good, free information on the internet. The 'price' is that you need to invest the time to 'study' and understand it rather than just give it a quick read. Even with a written explanation, understanding is often difficult to come by. In the case of carbs, much of what is going on inside is invisible to the eye, and not intuitive to the mind. Understanding requires more than skimming a paragraph; but given that our vintage cars all use carbs, it's worth the effort to work for a little understanding.

Regards,
Tim Engel
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PostPost by: Chancer » Wed Jul 02, 2014 8:08 pm

For those of us who grew up with old bangers with worn out carbs all of the above became intuitive but I could never explain it to someone, hats off to those of you who have managed to do so.

And then on cooking engines that needed the choke you would get that situation when the points closed up or the engine was generally out fo tune where it would not start and run without the choke but it wouldnt run with it either, it would juice (or choke) up and you had to be equally skilled with the throttle to tease it above this to the revs where it would clear its throat.

Ring any bells anybody?

Glad those days are over, dragging the battery out to the car from the warm (relatively) house, connecting it up, off with the air cleaner and a squirt of de-icer down the carb throat (the stuff was volatile in those days) then a bit of cranking and usually then out with the starting handle.

Ballast resisted coils really did make a difference in those days.

My late cousin learned to drive in South Africa, when she moved back to England she had a newish Polo, twas around the early 80's because it had a choke, she knew she had to use it to start the car but when she stopped at the shops it wouldnt re-start, they guy who got her going again made her feel really small, she didnt know that she had to progressively push back in the choke, which by the way, here in France is called le starter

Have you ever tried to explain to someone especially a woman who has been driving for years how the choke should be used? Not easy.
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PostPost by: Esprit2 » Wed Jul 02, 2014 8:24 pm

Chancer wrote:For those of us who grew up with old bangers with worn out carbs all of the above became intuitive but I could never explain it to someone, hats off to those of you who have managed to do so.
(Snip)...
Have you ever tried to explain to someone especially a woman who has been driving for years how the choke should be used? Not easy.
I did grow up in those old days of carburetors and breaker points. Normal maintenance was required at 5000 mile intervals, and I spent many a Saturday morning as a kid 'helping' my dad adjust/replace breaker points, time the ignition, and adjust the carb. I was doing it on by own before my teenage years. It was just normal life, everybody did it, and understanding was almost at a genetic level. Now, not so much.

The first rule to Driver's Education is to 'never' attempt to teach your wife, or any female with whom you have a close/ family relationship how to drive, or anything about cars. You will not come out of the experience ahead of the game... ever.

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Tim Engel
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PostPost by: Galwaylotus » Wed Jul 02, 2014 8:56 pm

Esprit2 wrote:
Chancer wrote:The first rule to Driver's Education is to 'never' attempt to teach your wife, or any female with whom you have a close/ family relationship how to drive, or anything about cars. You will not come out of the experience ahead of the game... ever.

Regards,
Tim Engel

Well I taught my two daughters to drive on a 1990 Mini 998cc and they both still talk with me and give me nice presents on my birthday!!! :lol: :lol: :lol:
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PostPost by: Chancer » Wed Jul 02, 2014 9:17 pm

Such is the disconnect between the driver and the engine in modern cars due to fly by wire throttles, engine management, emissions control, idle stabiliser circuits, automatic enrichment, lamda zero (or is it one?) mapping that you really cant feel if your engine is performing as it should.

I have bought a few old and new generation vehicles that I could tell were in good mechanical shape but just lacked the urge that I would expect from them, long are gone the days when they may have needed decoking although the symptoms were identical, in both cases someone had got one cam out by one tooth, at least on the ones with carbs and a means of advance retard if not a Dizzy I could have a play and then know pretty much what the problem was, with modern vehicles it would just feel as flat as many other vehicles hiding the fault.

I have just freed off the vanes in the turbo of my diesel engine with oven cleaner (I know, i know, :roll: :roll: ) I have had the fault for 7 years, the turbo would drop out until I did a hot ignition restart, initially I worked out how to live with it (the restart) then how to avoid it, slow gentle warm ups in winter then what the fault actually was and how to fix it, OK I have been quite lax in attending to it but what shocked me is just how much better the vehicle now performs, the throttle response is better than it ever has been in the 9 years of my ownership. I really thought that it was just another flat and uninspiring modern vehicle which of course it is but its a lot better than it was :D
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PostPost by: mbell » Thu Jul 03, 2014 12:24 am

Chancer,

Have you ever visited the US and driven a modern car here? I was amazed at the difference, if you think Europe is bad you should try it here. The engines are so flat and have no life at higher revs. I put down to the even stricter emission regs and the result is everyone drives much buffered engines cars and generates lots more pollution!
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: Chancer » Thu Jul 03, 2014 10:17 am

92 was the last time and the new cars I drove then felt terrible compared to then current european ones, now our current vehicles are as I remember those in California so I guess yours must be very unrewarding.

I drove a Peugeot diesel once quite spiritedly, or at least I tried to, it gave me a sprained ankle, most modern ECU's will electronically slow down the commands to an engine from a rapid throttle movement to reduce transient emissions, this car had a hydraulic or pneumatic damper on the throttle pedal, push it down slowly no resistance felt, push it down fast and you get muscle pain but no quicker engine response.
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PostPost by: mbell » Thu Jul 03, 2014 7:39 pm

Chancer wrote:92 was the last time and the new cars I drove then felt terrible compared to then current european ones, now our current vehicles are as I remember those in California so I guess yours must be very unrewarding.


I wouldn't say it has instance throttle response, but it does respond, pull and is far from flat at high revs. Wanting a "affordable" second had car that was decent to drive and had a manual gear box, gave very few choices basically BMW 3 & 5 series and the odd Porsche 944. Found a nice 1 owner e39 5 series, almost all the manuals here are 540i so end up with the 4.4 v8 :twisted:

Most cars are terrible thou (and not just on throttle response). Getting a car next week from San Francisco next week, they always find me something that goes straight to the top of worse cars driven. Will be interesting to see if they do it again!

(P.S. sorry for diverting the thread away, the carb discussion was very good and informative)
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: Quart Meg Miles » Thu Jul 03, 2014 11:00 pm

St Wilkins claims you don't use the Webers' "choke" to start but I used to with the original 40-18s. Then I had second hand 40-31s and now, for many years, new 40-151s and the latter won't run at all with the choke out a tiny bit even in very cold conditions. I haven't investigated it as four pumps are good for very cold and none in summer and it idles almost immediately in all cases.

So, it may depend on which particular items you have whether it is worth making the choke active.
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PostPost by: Grizzly » Thu Jun 06, 2019 1:44 pm

I'm just reading old posts about Choke or no choke to start from cold......

I have been spending allot of time setting my 40DCOE's up and found the stock Lotus jets made the cruise REALLY rich but the knock on effect was it started with a pump of the throttle from cold (no choke, assuming it had fuel in the bowls) moving on i now have quite a lot smaller Mr Franck's jets fitted so my cruise is very close to 14 afr, that has dramatically effected my MPG but also means my car just won't start without the choke...... if i give it a pump of throttle it will just sputter a bit (almost like trying to start a car thats run out of fuel) but put the choke on maybe 1/4 of it's travel and it starts every time.

Guess the moral of the story is the better you get your tune the more likely you are going to need the choke.
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PostPost by: RichC » Thu Jun 06, 2019 3:29 pm

Tru Dat , Grizzly 8)
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PostPost by: Slowtus » Thu Jun 06, 2019 4:07 pm

Chancer wrote:Have you ever tried to explain to someone especially a woman who has been driving for years how the choke should be used? Not easy.


Taught my long suffering to drive when we lived in London - car was a '65 Cortina GT with a badly flowed head, aggressive cam and a PAIR of 40 DCOEs and it was very lumpy at idle (all down to me for doing a lousy job on the head, selecting a silly cam and insisting on twin Webers when a simple single would have done very nicely...).

Which meant she either had to use the choke and/or do the accelerator pedal dance until everything kinda settled down and she managed perfectly well once she learned the techniques required, always factoring in the ambient temp, humidity and direction of the wind :D

She failed her driving test in this car...nothing to do with the driving, it was that damned '3 point' turn that did her in, somehow she just couldn't wrench the wheel as needed to get it done right, must have been those massive 185 section tires!

Passed the next time in a basic 850 Mini with 'normal, skinny section tires :D and yes, the "choke" was involved with the Mini, no way you could start without a choke on that SU...I did wonder for a time why the term 'choke' was used until someone explained to me that engines do not drink, they breathe and by choking the air...

I don't recall either of us using the choke in our S2, even in the dead of winter in chilly Bedford though.
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PostPost by: billwill » Fri Jun 07, 2019 12:57 pm

The thing we generally refer to as a choke on the Weber carbs isn't really a choke at all. Its a small extra complete carburettor set permanently (?) to give a rich mixture, so the actions described above are wholly expected.

In fact I think the Weber documentation calls it a 'starting device'.

Dellorto carbs similarly have a starter carb, not a choke.
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PostPost by: Grizzly » Fri Jun 07, 2019 1:08 pm

Yep but it will just start confusing people thanks to Lotus writing 'Choke' on the dash. Weber called it a starting device because a 'Choke' is just another name for a venturi and of course that has nothing to do with the cold start.


What i find interesting is my Elan with stock jets etc fitted was bang on 12.5 afr through a full throttle run but cruising it was closer to 11 afr. I don't know how they set them up back then and maybe modern fuel hasn't helped either but i find it odd the Main circuit seems quite well set up and the cruise is so out of wack....... so maybe they struggled with the suspect Weber Idle jets or the badly placed progression holes? (just made it rich to cover all the lean holes) I really see why there are people who dedicate large amounts of time setting Dcoe's up.
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