Date: Fri, 26 May 1995 08:10:56 -0600 Subject: Weber Carburetor Adjustments: Here's How!Having seen two requests for info on adjustment of Weber carburetors in the last few days, and having just installed one on my `63 IIa (I've still got the manual!), here goes:
This is specific to a 1 bbl Weber replacement "economy" carburetor jetted for Landrover 2286cc by Weber (it is a 34-ICH). (By the way I get about 15 mpg with this thing -- much better than the to 10 mpg from the kludged Rochester from an old Jeep it had before, but worse than my old `67 109 with a Solex (sometimes up to 20 mpg) -- better power than both though!). As you may know, these carbs were used on lots of vehicles, they can be adjusted for each type by replacing the proper jets, etc. My father in law has a Weber Book describing all of these adjustments and modifications in detail -- he was able to adapt a Weber 2bbl from a Ford Pinto to an Opel GT with jets purchased from a speed shop in california (called Crazy Larry's or some such).
Here's the info from the Weber Landrover Installation instructions:
Calibration:
ITEM Part # Size Main choke ........ 27 Auxiliary venturi 70311350 35 Main jet 73801165 165 air corrector 77201190 190 emulsion tube 61440211 F6 idle jet 74409050 50 pump jet 76407055 55 pump back bleed 79701040 40 needle valve 79531175 175 Float Level (with gasket) 7mm +- 0.25
MIXTURE ADJUSTMENTS
1. Start engine and maintain approximately 1200 rpm until normal operating temperature is attained and the choke can be fully returned.
2. Set engine idle speed to approximately 850 rpm, by adjusting the throttle stop screw.
3. Adjust idle mixture screw to obtain the highest engine speed.
4. repeat steps 2 and 3 as necessary so that the highest attainable engine speed by adjusting the mixture screw is 850 rpm.
5. The final adjustment is made by turning the mixture screw approximately half turn clockwise to weaken the mixture and so obtain the exhaust emission value of CO 2.5-3.0% Vol. The engine speed should now stabilize at approximately 800 rpm.
THAT'S IT!
In one of the messages, one fellow's vehicle had failed emissions -- he then asked (among other things) what the point dwell angle should be. I enquired from British Pacific about this once, the fellow put me on hold and called a mechanic friend of his, the value he quoted was 57-63 degrees. I carefully adjusted my points with a feeler gage and then checked the dwell immediately after and, BINGO, 60 degrees!
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| `63 | IIa | Stephen Brown
|______|_______| Geomechanics Department, MS-0751
/___/^^^^^^\___\9 Sandia National Laboratories
|oo|(@)##(@)|oo| Albuquerque, New Mexico 87185
| | [####] | |
======%%%%====== email: srbrown@sandia.gov [5/'95]
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From: Trefor Delve (delve1t@nectech.co.uk) Subject: Weber Carbs Date: Wed, 06 Sep 95 13:43:00 GMTre. your query on Weber Carburettors.
Whilst I am not an absolute expert on Webers, I do have some experience in their use - enough at least to outline the basics. The principle of the carb is simple - however, its setup is complicated.
First of all - the numbers:
The number refers to barrel diameter in mm. The DCD is a twin choke and is really referred to as a 28/36 DCD; the 28 being the primary barrel diameter, 36 being the secondary diameter. With the 38 DGAS, the barrels are the same diameter: 38 mm.
Internals:
Components that affect the setup are Main jets, emulsion tubes, air correction jets, venturi sizes. Consideration needs to be given to the idle jets although this is not really a perfomance issue. The setup of the carb strictly speaking requires a dyno but I'm sure that there are people with a great deal of expertise in the setup.
The differences:
The difference between the carbs you have are in their application. The 38 DGAS is intented to be fitted to 6 cylinder engines with a manifold such that each barrel of the carb feeds 3 cylinders only. In effect the DGAS consists of two separate carburettors with a common fuel supply and synchronised throttles.
The 28/36 DCD on the other hand may be fitted to 4 or 6 cylinder engines BUT the unit is intended to supply ALL of the cylinders. The function of the two barrels is to provide a compomise between economy and performance. As you quite rightly pointed out, the second choke only opens when the demand from the thottle is high. In fact, the secondary choke does not open until the primary choke is 2/3 open.
The principle used to improve the economy with the DCD is directly related to the smaller barrel and hence smaller venturi. With a smaller venturi, better fuel atomisation is obtained when the air flow through the carb is small.
Another difference between the carbs is the principle of the cold start operation. With the DCD, the cold start device can effectively be considered as a separate carburettor. With the DGAS there is a conventional choke at the top of each barrel.
Presumably, if there is someone who produces a manifold allowing this to be fitted to your SIII, then there should be someone who can set it up.
Hope that this helps in some way.
If anyone out there spots any problems in the above, please let me know as I am clearly misinformed.
Trefor - tdelve@nectech.co.uk