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    Thread: FAQ - Carbs

    1. 03-13-2004 12:03 PM #1
      Quote, originally posted by GTaye »
      Ever wonder?
      (Stolen from

      Basics of Motorcycle Carburetor Operation

      The basic secret of carb function is that inside each carb are thousands of tiny gnomes; each with a small bucket. As you open the
      throttle, more of these gnomes are allowed out of their house and into the float bowl, where they fill the buckets and climb up the carb's passages to the intake, where they empty their buckets into the air stream.

      But, if you don't ride the bike for a while, bad things can happen.
      Tiny bats take up residence in the chambers of the carb, and before
      long the passages are plugged up with guano. This creates a gnome
      traffic jam, and so not enough bucketfuls of fuel can get to the
      engine. If it gets bad enough, the gnomes simply give up and go take a nap. The engine won't run at all at this point. Sometimes you'll hhave a single dedicated gnome still on the job, which is why the bike
      will occasionally fire as the gnome tosses his lone bucket load down
      the intake.

      There has been some research into using tiny dwarves in modern carbs. The advantage is that unlike gnomes, dwarves are miners and can often re-open a clogged passage. Unfortunately, dwarves have a natural fear of earthquakes, as any miner should. In recent tests, the engine vibrations caused the dwarves to evacuate the Harley Davidson test vehicle and make a beeline for the nearest BMW dealership. Sadly, BMW's are fuel injected and so the poor dwarves met an unfortunate end in the rollers of a Bosch fuel pump.

      Other carb problems can also occur. If the level of fuel in the float bowl rises too high, it will wipe out the poorer gnome housing in the lower parts of the carb. The more affluent gnomes build their homes in the diaphragm chamber, and so are unaffected. This is why the bike is said to be "running rich".

      If the fuel bowl level drops, then the gnomes have to walk farther to
      get a bucketful of fuel. This means less fuel gets to the engine.
      Because the gnomes get quite a workout from this additional distance,
      this condition is known as "running lean".

      The use of the device known only as the 'choke' has finally been
      banned by PETG (People for the Ethical Treatment of Gnomes) and
      replaced by a new carb circuit that simply allows more gnomes to carry
      fuel at once when the engine needs to start or warm up. In the
      interests of decorum, I prefer not to explain how the 'choke'
      operated. You would rather not know anyway.

      So, that's how a carburetor works. You may wish to join us here next
      week for basics of electricity, or "How your bike creates cold fusion
      inside the stator, and why the government doesn't want you to know
      about it."

      Modified by GTaye at 4:59 PM 9-8-2004


      Modified by the12for12 at 10:37 AM 6-21-2007

    2. 03-13-2004 12:36 PM #2
      Carbs - The Basic

      The usual tuning last for the N/A motor includes for the most part, headers, muffler, exhaust, hi-profile cams, high comp pistons... But have you considered carburetors? Here's a look at the classic but effective form of N/A motor induction.

      When one thinks of high performance carburetion applications, we tend to imagine funneled intake making that nice classic induction noise...

      One of the major advantages in using the carburetors is in it's throttle response. This is more apparent in the racing field where no filters or collectors are used in the intake. Also, compared to the single throttle injection, the Mikuni and Weber style side-draft uses dual, 2 barrel throttles for a total of 4 individual throttle mechanisms to mix the fuel and air with more control and immediacy, resulting in a positive production of gasoline/air mixture, and in turn making potentially more torque than single throttle. As you may know, there are 4 throttle, fuel injection mechanism too. And the resulting principle is similar. The two systems do have very similar, and distinct advantage over the single throttle setup.

      So, what's so hot about using carburetors?

      Well, here are some characteristics you may find attractive:

      First of all, carburetors need no intervention of ECU's which can be both expensive and in most cases limited in adjustability, unless expensive alternatives like those programmable variety is in your budget. Although it takes some practice, setting a carburetor can be as simple as changing the jets and monitoring air/ fuel ratios. The goal is to match the jets within the carburetors to the required spray pattern and volume to desired mixture at a given rpm and vacuum. There are usually main jets and sub jets for various compensation, both of which have to be manually setup.

      Second, the carburetors can be adjusted for much wider variety of engine setups using the same unit for the most part. Since the carburetor's adjustment is in the jets alone, it can accommodate almost anything you can long as it's normally aspirated. (Well, some forced induction setups exited in the past but all of them are running fuel injection now)

      Third and my favorite reason for the carburetors is the esthetics... The setup simply looks really nice!!!! and it sounds mean! Once an addict, you'll never go back.

      So why don't you install them right away?

      Well, there are some stuff you should be aware before you jump in.

      Since carburetors work with very narrow, optimized range, the more you set it for peak performance in one area, the more you will run into substandard operation in other areas. For example, the carburetors cannot compensate for difference in gasoline or effects of climatic temperatures and pressures on it's own. This adjustment is left to the owner to re-adjust each time. Though carburetors do operate very well in most conditions, the fuel delivery under many different conditions is usually much more accurate with modern electronic fuel injection. And usually much more efficient.

      For those who likes to tinker or wants optimum mixtures for a narrowly focused field, this can be much fun. Certainly, you will get attention from those not so inclined when you fiddle with carburetors on the spot and get good results. Race mechanics are often admired for such talent and gets gratification from that alone.

      But at the same time, it's certainly a chore for those who likes to me free of maintenance tasks or depend on it to commute every day. You must be frequently prepared to re-jet them or make adjustments when weather changes dramatically. For sure, those who live in areas with drastic seasonal climate changes will have to make adjustments all throughout the year, to keep it in top shape, and sometimes even just to start the engine.

      Keeping the above precautions in mind, the carburetors are seriously rewarding piece of equipment, and once it is running correctly, it's hard to beat with even the best fuel injection in terms of response and torque output...

      footnoted from


    3. 03-14-2004 11:28 AM #3
      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


    4. 03-15-2004 12:53 PM #4
      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.



    5. 03-15-2004 12:56 PM #5
      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.



    6. 03-16-2004 06:28 AM #6
      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....


    7. 03-21-2004 03:52 AM #7
      bump for some good info

    8. 03-21-2004 11:28 AM #8
      Basic weber carburetors settings

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


      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


      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 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.



    9. Member g60vw's Avatar
      Join Date
      Oct 3rd, 2002
      Anchorage, AK
      83/4 Rabbit w/ 2067cc 16v, 75 4dr ST, 85 4kQ for DD'n, F-350 haulrig, and Richard Pryor
      03-21-2004 08:49 PM #9
      AWESOME info!!

      Needs to be a sticky.


      Quote Originally Posted by wilm13 View Post
      I refuse to say anything but A1, A2 and A3. As far as I am concerned VW stopped making cars after that.

    10. 03-21-2004 10:35 PM #10
      Could you cover ignition/rev limiter next

    11. 03-22-2004 06:51 AM #11

      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.

      2.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.


      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.



    12. 03-22-2004 11:15 PM #12

    13. Member vdubjunkie37's Avatar
      Join Date
      Oct 25th, 2003
      Groton, CT
      2000 BMW 540i/6 Sport, 2003 Mazda Protege5
      03-28-2004 11:27 AM #13
      Quote, originally posted by g60vw »
      AWESOME info!!

      Needs to be a sticky.


      i second that.

    14. 03-28-2004 10:19 PM #14
      Timing without detonation please.

    15. 03-29-2004 08:47 AM #15
      Quote, originally posted by Redline Evangelist »
      Timing without detonation please.

      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.



    16. 03-31-2004 02:14 PM #16
      Are these tuning guidelines as far as jets go applicable to all carbs, ie a sportbike setup?

    17. 04-01-2004 02:14 PM #17
      Quote, originally posted by 89sport »
      Are these tuning guidelines as far as jets go applicable to all carbs, ie a sportbike setup?

      I'm not too sure, but I'll find out for you, OK?

    18. 04-01-2004 03:21 PM #18
      12.........hey kid i was reading the good stuff about the MSD box....i am running that same box, will that short it out reversing the wires?, and will it last if you do that? i bought my A2 with it all good to go and the timing gear rounded out and took out all my intake valves before i got to jump into it further and play with you have the diagram for that box, so i can see if indeed they did that......the car is kind of been half azzed so i am trying to sort thru all the ghetto rigging that they did..........thanks in advance........oh by the way she was running 13.6's before the little mishap.....

    19. 04-01-2004 10:17 PM #19

      Kool questions, but I'm running Jacoubs stuff personally . Gimme a minute I find what you're asking for , OK?


    20. 04-01-2004 10:53 PM #20
      Thomas, sent you an IM

    21. 04-02-2004 08:31 AM #21
      jacobs is the shizzle........i ran that back in the day when i was into aircooled, absoultely loved it........but my car came with the MSD so i am just going to stay with it.......

    22. 04-03-2004 07:39 AM #22
      Quote, originally posted by asnvolks »
      12.........hey kid i was reading the good stuff about the MSD box....i am running that same box, will that short it out reversing the wires?, and will it last if you do that? i bought my A2 with it all good to go and the timing gear rounded out and took out all my intake valves before i got to jump into it further and play with you have the diagram for that box, so i can see if indeed they did that......the car is kind of been half azzed so i am trying to sort thru all the ghetto rigging that they did..........thanks in advance........oh by the way she was running 13.6's before the little mishap.....

      Hopefully this helps to clarify some of your concerns.


    23. 04-03-2004 07:52 AM #23
      Quote, originally posted by 89sport »
      Are these tuning guidelines as far as jets go applicable to all carbs, ie a sportbike setup?

    24. Member FastLapRSII's Avatar
      Join Date
      Jul 15th, 2001
      Mk3 GTI 8V
      04-05-2004 01:20 AM #24
      What's the fuel PSI of the stock in-tank fuel pump?
      Could this be used after eliminating the main pump and housing?

    25. 04-05-2004 04:14 PM #25
      i don't believe so.......i have never heard of anyone using that pump........the pump for carb set up is very cheap.......i ran out and bought a getto pump after this nice expensive pump on the car quit working and have been running with it ever zone $30 bucks......and of course running a fuel pressure regulator set to 2.5 (didn't have to replace that, but pretty cheap as well i am sure)........

    26. Member RaceJetta's Avatar
      Join Date
      Oct 18th, 2002
      Ontario, Canada
      2010 R8 V10, Jetta Racecar, '98 GTI, '11 335ix
      04-05-2004 09:40 PM #26
      I use the intank transfer pump on my Mk2 racecar. With a pressure regulator, it provides more than enough fuel and pressure.

    27. Member FastLapRSII's Avatar
      Join Date
      Jul 15th, 2001
      Mk3 GTI 8V
      04-06-2004 12:44 AM #27
      Seems like a high volume/low pressure pump to me.
      Glad to hear someone has tried this!

    28. 04-06-2004 06:13 AM #28
      Quote, originally posted by RaceJetta »
      I use the intank transfer pump on my Mk2 racecar. With a pressure regulator, it provides more than enough fuel and pressure.

    29. Member glibobbo21's Avatar
      Join Date
      Nov 11th, 2002
      04-06-2004 06:21 PM #29
      this is great

    30. Member
      Join Date
      Feb 11th, 2003
      Winchester, VA
      05-04-2004 08:31 PM #30
      What do the terms DCOE and IDF mean, when talking about Webers?

    31. Member
      Join Date
      Apr 27th, 2003
      oregon city, oregon
      79 rabbit
      05-07-2004 09:59 AM #31
      can i use the bosch fuel pump and accumulator with carbs? i have a 2.0 liter 16 valve motor going in a 79 rabbit with motronic but might switch to carbs. both the accumulator and fuel pump are brand new. thanks

    32. 05-08-2004 11:41 AM #32
      Anyone know where I can get parts for dellorto's? Specifically for 45 DHLA? TIA.

    33. 05-10-2004 08:31 AM #33
      search Ebay

    34. Banned Rabbit 16v's Avatar
      Join Date
      Feb 3rd, 2002
      05-16-2004 06:36 PM #34
      Quote, originally posted by candm »
      can i use the bosch fuel pump and accumulator with carbs? i have a 2.0 liter 16 valve motor going in a 79 rabbit with motronic but might switch to carbs. both the accumulator and fuel pump are brand new. thanks

      Absolutely not. You will blow out all the seals and gaskets from the carbs. The FI pump operates around 80 psi. Carbs use between 4 and 7 psi . Anything higher is damaging to the carbs and definitely a fire hazard.

    35. Member
      Join Date
      Aug 15th, 2000
      Corvallis, OR
      05-25-2004 02:29 AM #35
      Quote, originally posted by noypiesky »
      Anyone know where I can get parts for dellorto's? Specifically for 45 DHLA? TIA.

      If you haven't tried CB Performance they have a lots of Dell parts. Alternetely check out I ordered my chokes from them and they showed up in like 4 days. I was really impressed.

      '83 GTI 2L Dell 40's (crashed)
      '86 Cabby ABA/SDS - Bitch Basket
      '07 Tundra -DD - more front travel than a Raptor

      West Coast President - Dubsquad Conglomerate International

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