What do weber carbs do

This engine features a well-ported cylinder head, higher compression, more cam, and many other performance tricks. It makes good power throughout a big rpm range. The chassis dyno figures always include driveline loss, hence the lower figures for the MGB.

Context is king when choosing a carb setup. So, the numbers show the Weber DCOE winning by a hair, but each setup produced nearly the same numbers. As a result, many people feel that a properly dialed-in Weber provides slightly crisper throttle response.

Another drivability consideration is our ignition system. Most importantly, a vacuum advance increases cruise and idle drivability as well as engine smoothness. If we plan on dialing in things in once and then basically forgetting about it, any carb is fine. However, if we like to tweak our tuning, the DCOE is probably the easiest to service.

Other SUs H and HS models have their idle mixture controls hidden underneath the carbs, so reaching and adjusting them can be an exercise in contortion. Further mixture work with the DCOE comes through the removal of a wing nut followed by a few turns of a screwdriver—the process is very simple and fast. SUs are nearly as easy: three screws to remove the carb top followed by another screw to change the needle.

DGVs are probably the least convenient to service. To change the jets, the air cleaner as well as the whole top of the carburetor must first come off. Emissions are another factor. SUs can easily be equipped with factory PCV systems and work with the evaporative loss systems that absorb fumes. Many Weber setups lack provisions for these things.

Another thing to consider: Who do you know? If your friends in the sports car community are Weber people, maybe you should follow their lead. That way you can freely exchange knowledge and parts with each other.

The same is true if you hang out with SU people. The last consideration, whether you want to admit it or not, deals with aesthetics. Maybe you like the look of polished dashpots. Or maybe you need two—or three! After all, you pick your paint colors and accessories for aesthetic reasons, so maybe your engine compartment choices should follow suit to some extent. Looking for some concrete answers? Both SUs and Webers have their strengths and weaknesses.

Either is good and neither is perfect. Weber carburetors might not be the induction of choice for a modern, high-tech, race engine. By that time, many of the Sixties-era race cars had been long sold-off, retired, or just pushed into the corner and covered-up.

Around the late Seventies and early Eighties, a lot of these carburetion systems were available used, and they could be bought fairly cheaply at swap meets. Understanding them, and getting them to drive on the street was entirely another matter, but they sure looked great. All it took was the time and patience of a few people who took a genuine interest in them at that time, and who saw a ready market for them in hot rods.

Weber carburetion tuners were few and far between, but a few shops popped-up that actually specialized in them. A carburetor is simply a device for the balance of fuel and air. You just have to understand the carburetor. Every circuit in a Weber carburetor can be addressed separately. Today, we know that the fuel level is oh-so-critical, so we pay a lot of attention to how the floats are set. And fuel pressure is the other huge factor.

We know we have to run a special, low-pressure regulator, usually set at 2. Compression ratio is very important when the size of the carburetors is considered.

Some engines need 44mm or 45mm carburetors, while other engines are more suited to 48mm carburetors. For instance, if you have a mild engine with 9. As you would expect, one of the biggest complaints about Weber carburetors is that the engine may run badly at the lower speeds.

There may be a lot of popping, blubbering, and possibly a flat spot. The jetting and timing have to be exactly right. The independent runner manifold makes for an extremely efficient engine; essentially, each cylinder is tuned individually. Please re-enable javascript to access full functionality. Posted 25 July - Hey guys, I've recently been working on a car with a multiple Weber setup four of them to be exact , and I've read a good bit about the venerated Weber.

I have two questions: First off, what was it about Webers that made them so great? That and the fact that some of them work sideways. The other question I have is, why multiple carbs instead of one big one? This car has four two barrel carbs. Really it's essentially four pairs of synchronized carburetors. It's a pain in the ass to tune and I'm turning over the job of rebuilding them to someone with more expertise.

Seems like the procedure of linking up the throttles and chokes to make them all work in perfect sync, plus of course tuning each idle circuit individually, leaves a lot to be desired. So what's the payoff? Posted 26 July - Posted 27 July - Posted 28 July - I have seen carbs that run miserably but still keep the car moving; with the new systems that don't happen.

No computer, no forward motion. I thought that a 'limp home' fallback was standard on all ECUs? Wouldn't necessarily help in all circumstances, but same applies to a carb too I presume. Posted 29 July - One of the major problems of early ECU ignition systems was the cost of programming. Ducati used a complete electronic ignition system on one of their bikes, iirc in the 80s.

The bike returned to points and bob weights the following model year, as the cost of reprogramming the system for the modified model was totally uneconomic on the size of Ducati production runs.

Obviously systems are much easier to reprogram now. Never take a pit place next to a Bultaco, Ossa or Montesa owner unless you like pushing bikes up and down pits. In the early 70's I sold my Ossa for a CZ. Shortly thereafter I became so aggrivated with bikes I went back to Mini Coopers. I have shelves of Weber bodies,parts and jets but love the SU' for simplicity and reliability.

I still have points in my car so I can fix them on the side of the road!. Posted 30 July - I have electronic ignition so it never needs fixing! The Bertone Alfas used to come with either Weber or Dellorto carbs.

Apparently the Dellorto ones had slightly better engine output and economy. David Visard used to build Dellorto bits into Webers on engines homologated with Webers. Posted 04 August - Posted 05 August - Did someone say Weber carbs [I know, late to the party] Posted 25 August - Were those Nissans you worked on the s?

With the geared overhead cams no belts or chains? Posted 26 August - No, Stanza's - the 's were mostly Jap factory only, not to be touched by mere Ozzies without 6 letters of permission signed in blood and in triplicate. Anyway, I was never an actual member of the team just an outsource. Bastards wouldn't even give me a shirt on events! That's an extremely efficient system. The only way a smallblock Ford can handle that kind of CFM is with an "independent runner" manifold.

So, in order to get drivability, throttle response, and lots of torque from the Weber-carbureted V8, the choke size is the first consideration. How big is the motor, what's the compression ratio, and what are you going to do with it? Once the correct size choke has been selected for your application, the jetting for all the circuits can be calculated around that choke size.

If you change the chokes which changes the cfm , you must also change jetting. On the other carburetors, the idle jet does it all. With the fuel and air that is measured in the idle circuit, the tuner can meter the right proportion of each during low rpm operation. The idle mixture is delivered in a ratio of fuel and air that the tuner decides on, and the total volume is regulated with the idle mixture screw, located on the lower part of each carburetor barrel.

On the IDA's, the air is metered in the idle jet holder; on the others, it's through a cross-drilled hole in the idle jet itself. The size of the fuel orifice and the size of the air bleed hole will determine the ratio The idle circuit is actually the low-speed circuit and must carry the engine all the way up to about 2, rpm, where the transition to the main circuit takes place.

That means if you don't drive over rpm, you're only running on the idle jets. After rpm or so, the idle circuit is entirely bypassed and no longer has anything to say. So, if you have a drivability issue, like a stumble, or rough spot that "goes away" after about rpm, that tells you to spend time tweaking the idle circuit. Or maybe the opposite is true. Either way, the two circuits are completely separate, so isolating the problem to a specific circuit is fairly simple. As mentioned above, one the most common gremlins with Weber carburetors is a seemingly incurable and very annoying flat spot shows up anywhere between 2,, rpm.

This condition is generally caused by one of two things. Either the wrong emulsion tube is in the carburetor, which is causing a rich stumble perhaps due to an under-emulsified mixture at that particular rpm range, or the idle circuit is too weak and falling off too early, not carrying the engine up to the point where the main circuit takes over.

When that happens, it leaves a "lean hole" that feels like a blubbering stumble. In the case of the wrong emulsion tube, there are really only a few that work really well for V8 applications.

If the flat spot is still there even with the correct emulsion tube, then you'll need to richen or lean-out the idle circuit. This is sometimes a tricky area, because the first thing you want to do is throw in a bigger idle jet, but sometimes playing with air bleeds, mixture screws, choke sizes, and timing can accomplish the same thing while sticking with the original jet size. I will admit, a little experience comes in handy here.

Sound advice can save a lot of time and aggravation. Drivability problems can be solved with a little tuning on your own or by relating the symptoms to someone who is knowledgeable enough to help you. Remember, these carburetors will do just about anything you want them to, as long as you know how to interpret the symptoms.

This circuit also has two basic calibration elements: the pump exhaust valve and the pump jet. The pump exhaust is a bypass valve located in the bottom of the float bowl. This is the piece that regulates how much fuel you want to make available when you need that pump shot. Putting a bigger bypass hole in the valve allows more fuel to bleed back into the float bowl instead of out of the shooters. The smaller the hole, the more fuel you're making available. You can even put in a "closed" bypass in, for when you need all the gas you can get.

The duration of the pump shot is varied by installing a larger or smaller pump jet shooter. Larger pump jets give a heavy blast over a short period, while the smaller ones will give a finer, longer-duration shot.

This circuit has three primary elements you should concern yourself with: the main jet itself, the emulsion tube, and the air corrector. In conventional carburetors, the main jet was all there is to work with. The main jet is stuck into the bottom of the emulsion tube and sits in fuel. As the carburetor begins to work, the main jet meters the amount of fuel allowed to pass through it and up into the emulsion tube. Air enters the top of the emulsion tube through the air corrector which meters the amount of air to be mixed with the fuel coming in from the main jet.

The air blows out of the emulsion tube through a series of holes along its length and aerates the fuel as it rises up the well around the tube.