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**Preen59** · 19-10-2008, 10:05 AM

Sidedraft - Data Reference

1.In carbs, bigger is not necessary better. Most engines that do not run well have chokes, main jets, accelerator pump discharge jets and/or fuel pressure that are too large for the engine, and running conditions.

2.It is not possible to tune an engine that has some mechanical problem. Well built engines respond perfectly to correctly tuned side drafts.

3.Electronic Injection vs. Carbs: Overall, the performance of these injection systems (if correctly set up) is unmatched by any carburetor but the differences between fuel injection and a well tuned side draft can be very small.

4.It is possible that changing to carbs will mean that your car will no longer comply with exhaust emission control or other regulations in your state or country.

5.An increase in engine power and therefore, performance, will mean that your car’s braking and suspension systems will need to be kept in perfect conditions and up rated as appropriated.

6.Engines last a lot longer if the air admitted into the engine is as clean as possible. Always fit the very best filtration system that you can afford to buy. Wire mesh filters over ram stack offer virtually no protection (except from stones) and can actually upset airflow.

7.Ram tubes, trumpets or air horns (stacks) should always be fitted to a modified engine. As a general rule:

1. Short ram tubes are usually used for high rpm applications.

2. Longer rams are usually used to maximize mid-range response.

8.Webers/Dellortos require high fuel volume not high fuel pressure, i.e., 1.5 to 2.5 pounds per square inch.

9.When tuning your engine the cost of buying parts has to be balanced against the actual cost of getting a specialist firm to carry out this work. It is possible to spend a considerable amount of money on jets, chokes, etc.(new or second-hand) that you will end up not using.

10.Very small choke sizes in large bodies is not a good idea. Overall recommendation: Fit the smallest choke that will give full power.

11.When a slight choke size reduction is necessary to achieve better low end performance (eg: out of a corner pulling power) then fit a choke size that proves best for the overall application.

12.Once the carburetors have been set-up to give optimum performance, you’ll still need to check them occasionally to keep them working at their best.

Check throttle spindle synchronization, float level, idle mixture and change fuel filter at regular intervals.

footnoted from http://www.club4ag.com/

**Preen59** · 19-10-2008, 10:11 AM

Selection and tuning of Weber DCOE carburettors

A very popular modification for kit car owners is the fitment of twin Weber DCOE or DCO/SP carburettors; these not only deliver the goods but also look very good. A good deal of mystique surrounds Webers, specifically Weber jetting and tuning. However Weber DCO series carbs are not as complicated as you might imagine, and whereas there is no substitute for a good rolling road session to tune them, there is much you can do to tune them yourself, by selecting the correct choke sizes and initial jet settings according to a fairly simple set of rules. This should get the engine running to a reasonable standard in preparation for the rolling road.

Arriving at the correct carb/venturi size

When selecting Webers, the most commonly asked question is "Should I have 40s or 45s" coupled with "Surely the 45s will give more power". This shows a basic misunderstanding of the construction and principles of operation of the DCO series. It is not the barrel size (40 or 45) which determines the airflow and therefore potential horsepower; it is the size of the main venturi or choke. Selection of the correct main venturi size is the first step in selecting the carburettor.

It is easy to make the assumption that biggest is best when selecting a main venturi size, but the purpose of the main venturi is to increase the vacuum acting on the main jet in order to draw in and effectively atomise the fuel mixture. The smaller the main venturi, the more effective this action is, but a smaller venturi will inhibit flow. A large venturi may give more power right at the top end of the power band, but will give this at the expense of lower RPM tractability. Only a circuit racer will benefit from this sort of compromise, on a road car, driveability is much more important. 95 percent of the time, a road engine is nowhere near its peak power, but is near its peak torque for 75 percent of the time. It is much more important therefore to select the main venturi for best driveability, once the venturi size has been selected, then the appropriate carburettor size can be arrived at.

Here is a small chart showing the available Main Venturi size for Common DCO series carbs
Size Available Venturi sizes
40 24-36mm
42 24-34mm
45 28-40mm
48 40-42mm
48/50SP 42-46mm
55SP 46-48mm

Below is a chart that will allow the correct selection of main venturi size for engines given the engines capacity and the RPM at which peak power is realistically expected to be achieved, for road engines peak power is usually between 5250 and 6500, depending on the cam selection. After the correct venturi size has been arrived at it is a simple matter to determine whether 40/45 or 48 DCOs are required, take the venturi size and multiply by 1.25, the result is then the ideal barrel size which will accommodate the venturi size selected.

Chart Showing Main Venturi Sizes for Various Engine sizes and RPM ranges

Carburettor Barrel size calculation

Venturi/choke size * 1.25

For example: a two litre engine giving its maximum power at 6000RPM will require a venturi size of 36mm, and therefore an ideal barrel size of 45mm (36 * 1.25). For this application 45 DCOE is the ideal solution, however a 40 DCOE will accommodate a 36mm choke, so if funds are limited and the engine is not going to be tuned further then 40 DCOEs will do the job.

If you have bought your Webers second-hand, it is important to understand that it is unlikely that they will be 'ready jetted'. However if you do not want the expense of changing the main venturis, you will still need to know their size, this is normally embossed on the venturi itself, so look carefully down through the main barrel of the carb from the air cleaner side.

Diagram of Main Jet assembly

Main Jet and Air Corrector Size Selection

A useful formula for the calculation of main jet size when the main venturi size is known is to multiply the main venturi size by 4. This will give a starting point for the main jet size which should be 'safe', again as a starting point the emulsion tubes can be selected from the table shown below, although for Pinto F9 or F16 will generally be OK. If your carbs are already equipped with these, then that will save you some money. Air corrector jet initial settings should be around 50 higher than the main jet.

Main jet size Venturi size * 4

Air corrector Main jet size + 50

Using these formulae, a venturi size of 36mm will require a main jet of 145 and an air corrector of around 190.

Emulsion tube Selection

Below is a table showing suggested emulsion tube type, for a given single cylinder capacity.

Cylinder capacity Suggested tube
250-325 F11
275-400 F15
350-475 F9, F16
450-575 F2

Using the above formulae, the ideal settings for a 2000cc Pinto with power peaking at 6000RPM (290 degree cam or above) are as follows

36mm chokes
F16 or F2 Emulsion tubes
145 Main jet
190 Air corrector

The 2000cc Pinto in just on the cusp of change for emulsion tube type between F16 and F2, if you already have F16 tubes, use them it is not worth the expense of change, they will just cause the main circuit to start marginally earlier. A 2.1 or 2.2 Pinto should however be using F2s although F16s will do the job acceptably well.

Diagram of Idle Jet Assembly

Idle Jet selection

Idle jets cause a lot of confusion; although their name suggests that they govern the idle mixture, this is incorrect. It is true that the fuel consumed at idle is drawn through the idle jet, but the idle mixture is metered not by these jets, but by the idle volume screws mounted on top of each barrel. The idle jets control the critical off-idle progression between closed throttle and the main jet circuit, it is this part throttle operation which is so important to smooth progression between closed throttle and acceleration and for part throttle driving. If this circuit is too weak then the engine will stutter or nosedive when opening the throttle, too rich and the engine will hunt and surge especially when hot. The technique for establishing the correct idle jet size is detailed later, but as a starting point 40/45f9 idle jets for a 1600 engine 45/50 f9 for an 1800 and 50/55f9 for a 2000 will get you out of jail free.

Below is a chart showing approximate idle jet sizes for given engine sizes, this assumes one carb barrel per inlet port E.G. two DCOEs.
Engine size Idle jet size
1600cc 40/45
1800cc 45/50
2000cc 50/55
2100cc 55/60

Establishing the correct idle jet for a given engine is not easy but usually an approximation will make the car acceptably driveable. If the progression is weak then the engine will nosedive when moving the accelerator from smaller to larger throttle openings. A certain amount of change (richer/weaker) to progression can be achieved by varying the air jet size on the idle jet; this alters the amount of air that is emulsified with the fuel drawn through the idle jet. If this does not richen the progression sufficiently then the next jet size up, with the same air bleed should be tried. Below is a small chart showing the most commonly used air size designations, running from weak to rich. Generally speaking start your selection with an F9 air bleed.

Weaker Normal Rich

F3 , F1 , F7 , F5 ,F2-F4 ,F13 ,F8-F11-F14,F9 , F12 , F6

The ones in normal use are F2,F8,F9 and F6.

footnoted http://members.aol.com/dvandrews/webers.htm

**Preen59** · 19-10-2008, 10:12 AM

Buying second-hand

When buying Webers second-hand ensure that they are a matched pair. Look carefully at the serial numbers on the top of the carbs, these should be the same, or very similar. If they are not then they are not a matched pair and may well give problems when trying to jet them, as the progression drillings could be different. Inspect the carbs very carefully before parting with your cash, check their general condition, check for fire/heat damage, check that the butterflies open and close smoothly and that the linkages are smooth in operation and the carbs don't stick open. A common problem with Webers is the attachment of the throttle quadrant to the spindle, these can wear and will give an erratic idle and progression which no amount of tuning will cure. It is important to note that Webers are very rarely 'ready jetted' so factor the cost of jets etc. when deciding on your purchase. Check the throttle spindles for wear, excessive wear here will bleed air into the engine and again will affect setting up dramatically. Servicing kits for Webers are relatively cheap so a neglected pair, provided that the above checks are carried out, can be restored to very good condition by a thorough clean and service, the servicing is not difficult but has to be done in a clean environment, using a methodical approach.

footnoted http://members.aol.com/dvandrews/webers.htm

**Preen59** · 19-10-2008, 10:14 AM

Fuel Pumps and Fuel Pressure

Fuel delivery is critical to the proper performance of any Weber carb. From a basic 32/36 DGEV to a set of Triple Sidedraft DCOE's. Webers rely on a stable full float bowl in order to mix the fuel and air correctly. Mechanical pumps very rarely do this. They pulse fuel instead of giving a smooth even delivery and the amount of fuel varies with engine RPM.

A Proper Electric Fuel pump will give the best performance and most stable tuning for any Weber carb application. We use only High Volme and Low Pressure pumps. Webers work best at approx 4 psi of fuel pressure (Not 2 psi like many of the older books stated.) and you need Volume not Pressure to keep the float bowl full.

We ONLY use the Carter Rotary pumps. They are High Volume (60-70 GPH) but only 4 psi. This is PERFECT for all Weber applications from a Single 32/36 DGV on a Truck, Jeep or Car to a Triple Sidedraft setup on a Road Race car making 300 HP...This pump DOES NOT and SHOULD NOT use a Pressure Regulator for any reason. That is why we use it....

Carter 4070 Fuel pump with Mounting Bracket

Problem Pump and Regulator setups:
These are combinations that many of you are using and you could be experiencing problems because of it.

Holly Fuel Pumps with Regulator:
This is a very common combination and it has alot of problems. The pump puts out too much pressure so you have to buy a regulator for it. The Regulator is just a restrictor that inhibits flow. This causes a huge loss of Volume and overloads the pump causing alot of noise and premature failure. This results in the float bowl going low or empty under hard acceleration and causes cornering problems.

Facet Fuel Pump:
This is one of those little square pumps with the transistor mounted on top that make a ticking noise all the time. These pumps are TERRIBLE. No volume and High Pressure. These pumps have been sold for many years with Weber and Mikuni conversions and have cause many people alot of tuning problems. They are a pulse type pump that delivers almost no volume (usually less than the stock mechanical pump did) and usually at High Pressure. This cause flooding at idle and lean out conditions under high load. Do not use them....

footnotedhttp://www.racetep.com/weber.html#websynch

**Preen59** · 19-10-2008, 10:16 AM

Basic weber carburetors settings

chokes; Main jet ; emulsion tube; air corrector; idle jet; pump jet; needle valve;

DCOE40

upto 90 BHP; 28; 112; F16; 180; 45F9; 35; 150
upto 120 BHP; 30; 120; F16; 180; 45F9; 35; 150
upto 135 BHP; 32; 125; F16; 180; 45F9; 40; 150
upto 145 BHP; 34; 135; F16; 180; 45F9; 40; 150

Weber DCOM caruburetors require slightly richer idle jets and bigger main jets

DCOE45

upto 145 BHP; 34; 135; F16; 165; 55F8; 45; 200
upto 175 BHP; 36; 145; F16; 165; 55F8; 45; 200
upto 210 BHP; 38; 155; F16; 165; 55F8; 45; 200
upto 220 BHP; 40; 165; F16; 165; 55F8; 45; 200

VW16v/20516v&1.9/GM 16v ; 36 choke setting
above 16v engines but modified ; 38 choke setting

DCOE float level should be set at 7.5mm

The settings above apply to stock engines.modified engines usually require bigger venturis bigger main jets and ofter bigger pump jets

Carbureting cars and motorbikes isnt a hard task if its done with the right attitude and patience.
Its basically all about being able to provide the engine with the correct stechiometric mixture thru all the 3 fases of the carburetor's transitions-idle,progression and main.a 14.7:1 air/fuel mixture is the optimal burning mixture for the engine.performance applications require slightly richer mixture.some simple and easy to remember procedures will solve most of the problems.
after the carburetos have been jetted at the basic, recomended setting for your specific application the next step is to install the carburetors on the manifold (all the jets can be changed if needed while the carburetors are on the engine-in 99% of all cases).
after verifying that everything that leads to the carburetors (mainly fuel pressure ,distributor advance settings and fuel pump) and after a simple and fast check that are no air leaks between the carburetors and the intake manifold (can be done with foam or water shaked with soap)the main task of jetting the carbs can be accomplished. **a cheap O2 sensor or a CO tester are most useful at this stage but the job can be also done by checking the spark plugs' color.these last two are to verify the richness or leaness of the mixture**.
Getting to the basic task of setting the jets just right for the application always divide the procedure in 3 phases;idle,progression and main circuit.

1.with the engine turned on-the idle screw should be turned out just enough to feed the engine on low revs with the butterflies closed. if the engine requires idle screws turned out too many turns then you are running too small idle jets.depending on the type of carburetors the optimal setting should be 1.5-6 turns out.

2.passing to the progression phase the verification should be done once accelerating slowly to 3000-3500rpm and once fast.there shouldnt be any hesitation on both trials.hesitation on the first slow test-when the pump jets dont come into action may indicate lean/rich idle jets or too small main jets.if the hesitation only occurs on the fast acceleration test then the pump jets are too small.try increasing the pump jets' size,shorten the acceleration pump lever's run or change the pump jets to the form of the that squirts the fuel right to the middle of the cylinders.carburetors with more progression holes require bigger idle jets then carburetors with fewer holes(the increased number of holes was produced in order to have a smoother transition fase from idle to main.An increased number of progression holes and an adjustable pump lever arm provide you with plenty of adjusting possibilities to get the transition right.these two elements are found in all the later types of Italian made carburetors-dellorto,weber (dcom and dcoe) and solex.if factories went out of their way to change the production lines for these last two element changes-there is a good reason for it.technology goes forward in time!(specially when the brand names are weber,dellorto and solex)).bigger main jets enriches the mixture on low and middle range RPM's while small air correctors enriches the mixture at high RPM .
often hesitation can be solved by merely opening the air-by-pass screws.this increases the air flow velocity .cars having long duration cams often require an opening of these air-by-pass screws to increase the idle air speed flow.(its also used to balance the air flow between the barrels).***please note that the air-by-pass screws are present in all the latest types of italian made dual barrel carburetors.sometimes they are stil tapped with very thin alluminum caps-that is how they came out of the factory after settings have been made.a little tap on them with a pointed tool will remove them for inspection and adjustments.always remember to seal them with some silicon to avoid dirt getting inside***.

3. the main circuit is adjusted by changing the main jets,air correctors and/or the emulsion tubes.a optimal setting should have the engine rev up clean with no flat spots.

4. Hesitation is a symptom of a lean or rich mixture in the same transition fase where it occurs.a look at the spark plugs will give you the right direction.correcting it involves change of jets,change of emulsion tubes(please note that lean emulsion tubes can often be adjusted for proper use by installing smaller air correctors),opening/closing the air-by-pass screws,adjusting the pump jet level's run and checking the float level(a higher float level leads to richer mixture and idle inconvenients).

5.99.5% of the italian made carburetors have the cold starting choke option.if you live in cold weather and the engine compartment space permits you to use it-then please use it.its most helpfull in starting the engine in the cold weather.

footnoted http://members.ebay.com/ws2/eB...a1750

**Preen59** · 19-10-2008, 10:18 AM

A.IGNITION

How to control the engine's ignition without an ECU is the most asked for answer. There are several way to do this, first being the easiest.

1.Aftermarket ignition control: Simply buy an MSD 6A(L) or Crane HI-6 ignition box and use the magnetic pick ups from the stock distributor and you will have a working ignition. I have not seen the Crane HI-6 used successfully, but it is cheaper than an MSD 6AL, and comes with a module (pill) less rev-limiter. I personally use the MSD 6A, without rev control. The typical belief of the ignition boxes is that they do not have a built in ignition advance. The 4AGE can run smoothly with around 20-30 BTDC static ignition timing. However, the MSD has a nice built in feature that is not found while reading the instruction manual. By reversing the magnetic leads, the MSD can give you a nice timing advance curve. You simply set the ignition at you want at idle (stock is around 10-15 degrees BTDC). As you blimp the throttle, you will find that the timing jumps to around 20-35 degrees BTDC. For more control over the timing, you can purchase an MSD ignition control box which allows full control of the timing curve.

Another plus feature of going with an aftermarket ignition box is the added spark power (with accompany coil). With carburetion, the fuel is not atomized as well as EFI injectors. Therefore, having a higher power ignition spark can only add power. Don't forget to go with lower resistance spark plug wires as well.

2.Stock ECU: If you already have the stock ECU wired up, there is no need to remove it necessarily. I have heard that the ECU can work the ignition control independently of the fuel system. You might get some error codes because the injectors and stock EFI manifold will be disconnected. This would be a cheaper way of doing the ignition. I have not seen this work personally, but theoretically, it should work.

footnoted http://www.geocities.com/ae82power/FAQ-carbs.html

B.Ignition Systems, Spark Output and Spark Advance

This is a serious topic that seems to get ignored even by professional installers.

The essence of a Weber conversion is that you are putting on a Larger carb that flows more fuel and Air to make more HP.
Most older cars that are getting these carbs installed on them had very bad Point and Condensor Igntion systems with very low spark output. These systems were barely adequate for a stock carb let alone a performance upgrade. Adding even a single 32/36 carb to an old BMW, Opel, Etc will overload the stock ignitions systems capabilities.
When you add Dual or Triple carbs you are really causing a problem. You are adding a bunch of extra Fuel and Air but not adding the extra fire needed to burn it properly. This results in jetting problems, rich running conditions, etc. If you are doing a conversion from a later model Fuel Injected car that had a decent Electronic Igntion system on it this will not be as much of a problem although you could have a problem with Spark Advance on these types of vehicles (Read below.)
When doing a Weber conversion on an older Point type Ignition car it is a MUST to at least do an upgrade to Electronic Ignition with a higher output Coil and good wires and plugs. This will allow you to jet and tune the carb to its maximum HP and Fuel Economy potential.
We use the Pertronix Ignition conversion on most vehicles with the Bosch Red Coil and good plug wires and NGK SPark plugs. On dual and triple carb conversion we highly recommend the use of the MSD Spark Amplifiers with the Electronic Ignition. This will insure you have enough spark to burn all that extra fuel you are throwing at it. The difference in HP, Idle Quality, Cold Starts, and Fuel Economy are all very noticeable when doing the Ignition upgrades.

Spark advance is the other problem you are faced with. Most factory carb equipped cars have vacuum advance distributors. This is fine when installing a 32/36 or 38/38 because they have vacuum advance ports int the carb but when installing sidedrafts you do not have this option.

DO NOT hookup the distributor vacuum advance to the intake Manifold. That does not work and is a common mistake we see. If you do that you will pull full advance at idle then as soon as you open the throttle it loose vacuum and the timing will retard quickly causing a big stumble or flat spot and very bad throttle response.

When running Sidedrafts you need to either get a centrifugal advance distributor or leave your vacuum advance disconnected and just run more initial timing. You usually need 12-14 degress advance at 1000 RPM and 36 degrees total by 3000 RPM for the carbs to react properly. These timing numbers are baseline estimates only and can vary from car to car. You have to make sure you do not have a detonation problem from too much advance.

footnoted http://www.racetep.com/webfuelspark.html#webspark

**Preen59** · 19-10-2008, 10:18 AM

Timing considerations

If you just add DCOEs to an engine and start it up chances are that it will idle poorly and occasionally spit out the front of the carbs. Modified engines and engines with DCOEs need more than stock advance. Stock advance is 4 degrees BTDC. You will probably need at least 8 degrees BTDC initial timing with a cam and DCOEs. With a cam a good idle speed should be 800-1200 RPM depending upon the duration of the cam. If the timing is too retarded the engine will not perform well below 3000-ish RPM unless you had very big idle jets. A way rich idle jet can mast a lack of spark advance and reduce cab spittings but will drastically decrease fuel mileage.

footnoted http://www.cruzers.com/~twakem...o.htm

**Preen59** · 19-10-2008, 10:26 AM

MSD wiring diagram with OEM ignitor.

**Preen59** · 19-10-2008, 10:31 AM

"Weber nomenclature is chaos"

The prefix is the size of the throttle plate, a 40DCOE has a 40mm plate.

The letters refe,r in italian, to the general type of the carburetor;
DC means doppio corpo or double throat
V/O means verticale/orizzontale vertical or horizontal respectively
I (in IDA) seems to mean invertito or inverted, although there are no updraft webers, the IDA is a downdraft

less consistent single letter designations:
E Die-cast carburetor
F Ford or Ferrari? application
V Weber with a power valve
A Water-operated automatic choke

An example of an exception, the 40DCOE in later Alfa use is neither die-cast or equipped with an electric choke. The E indicates a trapezoid mounting bolt pattern instead of the rectangular one of the DCO.
or
There may be three, as well as two throats, in a Weber IDA, and there is no choke at all.

Any number after the letters denotes a variation of the basic type, to date there are 10 known variations of the 45DCOE.

Braden, Pat. Weber Carburetors. HPBooks, 1988

**Oneofthegreats** · 19-10-2008, 10:38 AM

Whooo.

I read through alittle bit of it, but look's like I'll need the entire day.

Awesome info Preeny.

Bloody Awesome!!!

Well done

I like the bit about buying secondhand.

People take note.

Sometime's it's better buying brand new. That's my opinion anyway.

I'll still have Fuel injection though, even if it is K-Jet! Ha ha

**Preen59** · 19-10-2008, 10:44 AM

Tim, you know you love carbies, you're just afraid to admit it! There's more to come...

**Preen59** · 19-10-2008, 10:51 AM

**Preen59** · 19-10-2008, 10:53 AM

Wiring in a 8980 timing computer and a 6A or 6AL. using a VW ICM

**Oneofthegreats** · 19-10-2008, 11:01 AM

Originally posted by Preen59 View Post

Tim, you know you love carbies, you're just afraid to admit it! There's more to come...

True.

But I like Holley's!!! Ha ha.

I'd have a weber on a rotary though!

But If I had a rotary, it would be turbocharged & on Microtech.

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