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Weber Carbs  Rating:  Rating
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 Posted: 10-19-2008 05:03 pm
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jscott127
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I have a 74 JH, VIN # 14928 with Weber carbs. I cannot find any data on these carbs in my JH Shop Manual. Is there a source for data on the Webers' and do they require a choke? There isn't a choke knob on the dash so I believe these carbs do not require a choke. In am correct in this thinking?

jscott127

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 Posted: 10-19-2008 09:28 pm
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Gary Martin JH 15371
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The JH originally came with the dual Strombergs in most western markets. In Europe they were available with dual Dellorto two barrels. Weber two barrels were never factory on the JH. That's why they are not mentioned in the manual. Webers can be fitted to the JH using the Europian intake manifold, but people on the message board have mentioned that they are difficult to get right and usually have a flat spot in mid range driving. As for the choke, the JH came stock with a manual choke cable on the dash just below and to left of the radio. I'm not an expert on Webers, but it seems there should be some sort of choke mechanism. If you check the message board under carburators there is quite a lot of discussion on Webers and Dellorto's. Gary

Last edited on 10-19-2008 09:31 pm by Gary Martin JH 15371

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 Posted: 10-19-2008 10:33 pm
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Jensen Healey
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Webers and Dellortos (except competition models) have choke mechanisms. The Weber's is located on the manifold side of the body. The arm and cable stops should be clearly visible when viewed over the cam covers.

Weber and Dellorto carburetors have accelerator pumps which the stock Zenith Strombergs do not. If you live in a mild climate as I do, a few pumps on the accelerator shoots streams of raw gasoline into the intake tract. After starting, a bit of warm-up may be required so you will be confined to the cockpit until it will idle on it's own. Those with ZS carbs can pump all day with no effect and would be advised to confirm the proper functioning of their chokes. 

Webers do in fact have progression holes and an expert tuner should have no problem eliminating any flat spots. Most old Alfas have Webers so your local restoration shop may be able to help with any tuning issues.

Kurt

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 Posted: 10-21-2008 04:52 pm
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Arvin Appelman
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The Weber DCOE's have an enrichening circuit in place of a choke.  These circuits often get plugged on the Webers.  They draw fuel from the bottom of the bowl and any varnish or other contamination wants to settle there.  Kurt's suggestion for starting works fine. 

Chokes richen the mixture by restricting the air and enricheners do it by supplying more fuel.  General discussion is that the Lotus 907 and the Webers are not a good combination.  I have Webers on mine and I have not been able to get the progeression as smooth as I would like but, it is very drivable. 

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 Posted: 10-21-2008 07:31 pm
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Jensen Healey
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Hi Arvin,

At what RPM are you having issues? I know an Alfa restorer I can ask questions.

Kurt

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 Posted: 10-21-2008 08:44 pm
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jscott127
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Many thanks to the members that answered my carb question. They are Weber 45DCOE9s'. I bought the car from a person who had it stored for 10 years in Atlanta, never driving it. He knew nothing of its history except that it came from California. Thanks to Bruce Madden I have replaced the water pump and radiator, but have a problem with excessive oil blow-by and I am trying to install an  oil separator like the 73JH's have. Anybody know of a source? The car has racing seat belts but no roll bar at this time. Sure wish I knew more of its history and what has been done to the motor.  Thanks Again for the info.

Jim Scott

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 Posted: 10-22-2008 12:54 am
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Arvin Appelman
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Kurt,

2500 to 2700 rpm.  I can't remember exactly what the jetting is.  Should have written it done but I have tried several combinations and lost track.  I can pull them out if necessary.


Arvin

19492


 

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 Posted: 10-22-2008 04:11 pm
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Jensen Healey
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After re-reading Des Hammill's excellent book, here are my thoughts:

Webers and Dellortos are infinitely adjustable. The progression mixture is adjusted with the idle circuit and must be spot-on. I think your idle circuit is too lean. Optimize your air/fuel mixture at 2600 RPM! Get a richer idle air corrector and re-adjust 900 rpm running with the idle screws.

Determine is if the Carbs are an emission version. These have lean progression circuits. Check under the progression hole cover and see how many holes there are and their size. The more or the larger the holes, the leaner the progression. The DCOE 2 and 11 seem to be non-emission versions.

If you have an emission carb you may need a larger idle jet, perhaps 60 or 65, and leaner idle air corrector.

A CO test at your local smog shop can determine if your jetting is correct.

Kurt

 

Last edited on 10-22-2008 04:13 pm by Jensen Healey

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 Posted: 10-24-2008 06:26 pm
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Arvin Appelman
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Kurt,

I have pre-emmission carbs.  I will try your suggestions.

Thanks

Arvin

 

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 Posted: 10-25-2008 03:03 pm
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Greg Fletcher
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If you're running Webers, I don't think it's possible to completely eliminate that mid range popping. I tried for years and I can tell you that Dellortos are much better designed in how they handle progression.

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 Posted: 10-25-2008 03:34 pm
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subwoofer
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Just out of interest:
Wideband O2 sensor circuits are now really affordable, and provides data logging for additional channels. If you build a AFR/RPM/MAP table for your setup, how much practical experimentation is really needed to find a jetting that is sound for the entire RPM and throttle range? Given the starting point (the current jetting), it should be predictable how the interaction between the elements is, right?

The JAW wideband controller: http://www.14point7.com/JAW/JAW.htm

At the moment, I am running a pair of knackered Strombergs, but I will switch to Dell'Ortos or Webers (or Jenvey throttle bodies and a computer squirt if I'm lucky with the paperwork towards the authorities, at the moment it has to be "in original state"). Seeing the stories of jetting experiments, I believe there should be a much more scientific way of getting the desired results.

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Joachim

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 Posted: 10-25-2008 04:30 pm
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Greg Fletcher
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The progression problem with the Webers is inherent, it's not something you can eliminate by jetting. You can minimize it quite a bit, but if that sort of thing is bothersome to you (it is to me), then you might be better off with Dellortos. With Dellortos you can bolt them on, adjust the flow and idle and be driving around with no problems in 10 minutes.

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 Posted: 10-25-2008 04:50 pm
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subwoofer
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Got it. Means I should get a pair of used Dell'Ortos from Lotusbits and a rebuild kit then. Which is the better starting point, spec 9 or 10?
I will be changing cams and compression when I rebuild the engine (hopefully next winter), may also get a stroker crank. This winter is basics like running gear, locks and soft top.

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Joachim

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 Posted: 10-25-2008 04:59 pm
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Jensen Healey
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If someone has logged the difference in air/fuel ratio for each air corrector, it would be possible to make a more educated guess, presuming all of the other jetting is correct for the engine and it's intended use.

While the JAW looks fun, why not just buy a guage?

http://www.jcwhitney.com/Air-Fuel-Ratio-Gauges/600002105.jcw?in_dim_search=1

Dave Andrews has a jetting calculator but it's not for the 907. 

http://members.aol.com/DVAndrews/

I think the Club Store sells a good Dellorto kit that should get you really close if not spot on.

Kurt

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 Posted: 10-25-2008 06:31 pm
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subwoofer
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Don't think I'll fork out 5 to 10 times more to buy a Dell'Orto kit from the club store, when used setups from later Esprits are available for £2-300 in England. I am in Europe, remember.

The AFR meters from Whitney must be narrow band devices (given the price), so I doubt they will be any good at telling if you hit 12.5 or 11.0 AFR. The cheapest wide band controller I have seen apart from JAW is the LC-1, and that costs around $200 plus sensor and display, I think the MegaSquirt community would have noticed if there were cheaper solutions.

The jetting calculator could do with a makeover, btw. It was slight erratic on my machine, at least!

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Joachim

Last edited on 10-25-2008 06:31 pm by subwoofer

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 Posted: 10-25-2008 07:00 pm
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Jensen Healey
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I meant the jetting kit, not the carbs.

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 Posted: 10-25-2008 07:01 pm
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subwoofer
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Ah. Sorry, a bit slow there...

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Joachim

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 Posted: 10-25-2008 07:11 pm
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Greg Fletcher
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JC Whitney is well known in the US for selling items of dubious quality. I would be extremely reluctant to purchase anything from them. Just my opinion of course, but as far as Dellortos are concerned, it would money well spent for an owner to invest in a Morgan Carbtune Pro http://www.carbtune.com/. It's an old fashioned mechanical four port meter but you set both carbs at the same time. Dead simple to use and any DIY mechanic can figure it out in a few minutes.

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 Posted: 10-25-2008 08:47 pm
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subwoofer
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I've heard they are good, and possibly easier to use than the Unisyn I used when I (tried to) sync the carbs earlier this season. Drawing a lot of air in around the spindles and I may still have a vacuum leak or two, but it improved the situation a lot. I will get one, I think, they are only around £70.

The Unisyn was a bit cumbersome in use, we had a bit of trouble getting it to mate properly with the carb throat on the rear carb.

I agree that carb sync is essential for any results at all, but there must be people out there that have been using wideband O2 sensors for setting up engines with carbs? I can't really think of any other method (other than measuring the amount of fuel and air entering the engine) to determine how far off you are at any given moment?

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Joachim

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 Posted: 10-26-2008 02:05 pm
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Jensen Healey
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Hi Joachim,
Since no oxygen sensors were in general use when the JH was built tuning was done using Co readings. The manual states 1.2 - 2% Co at idle for the 4 speed and .2 - .3 % for the 5 speed as emissions were further regulated, (sounds kind of lean).


Judson has used exhaust gas temperature readings to tune Dellortos.

I prefer the seat of the pants method.

Kurt

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