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Member
Join Date: May 2009
Location: Lisbon
Posts: 66
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Carburettors, I shall miss you old friends
Seeing that carburettors are clearly on their way out, I thought that I’d write something in their defence, because I'm quite sad to see them disappear. Maybe I'm a bit biased because by now I know them quite well.
Apart from some 50cc mopeds, all road bikes in Europe today are fuel injected (FI). Only a few offroad bikes, up to 500cc, still use carbs, but not for much longer. Another year or so and they are history...
Why is this the case? As we have been told, one of the main reasons for swapping to FI is that it allows the engine manufacturers to reach better emissions standards, which are getting tougher. This is because injectors deliver just the right amount of fuel to the engine for its given running conditions. As a result they are more fuel efficient, and so pollute less. FI also has allowed the development of more powerful bikes, and because of the compactness of their systems, motorcycle designers have had more space to play with around the engine. This led to shorter wheelbases as well as better weight distribution. In a race environment, FI has taken out all the work of jetting and re-jetting the carb to find the perfect fuel mixture according to the track conditions, temperature, altitude etc., etc. FI does all this rather technical work automatically using sensors, which have allowed us to have all sorts of information on our instrument displays. Cool stuff. Sure that there must be a few more benefits.
Now what about carbs? I think we shouldn't forget that carburettors came in different designs, and were seriously developed on the later 1990s bikes. These high-performance carburettors (slide carburettors) are still used in some of today’s offroad bikes (up to 500cc).They have been developed to an extraordinary degree. A Keihin FCR-MX 41, for example, is an amazing carb, absolute state-of-the-art technology, great engineering, a 100% mechanical beauty.
Keihin, or Mikuni, carburettors got so highly developed that injectors didn’t have much more to offer. However, the demand for more powerful superbikes meant that engine designers needed straighter intakes with larger diameters. Slide carburettors could work well up to about 41mm and then struggled. Carburettors with bigger intakes were available, but not as efficient as the slide carb, and bigger in size, which in the case of a motorcycle, wasn't an option.
But really, in terms of performances up to say 500cc (per cylinder), these carbs are excellent in most riding conditions/situations. If the right mixture arrives in the cylinder, the engine doesn’t care if it comes from a carb or a FI system.
Carburettors do need more maintenance, and some parts will wear out with use, but they can easily be replaced and are relatively cheap. Also, if more than one carb is used then they need balancing from time to time. As far as reliability is concerned, I have found that they give little problems, if you make sure the fuel bowl is drained occasionally, and the fuel filter is regularly cleaned. Fitting another in-line fuel filter can also be a good idea. Carbs are less complicated than they appear. When they go wrong, it is mainly because of dirt blocking one of the jets, or that has accumulated somewhere. Cleaning them is again not such a big job, and it can be very rewarding... Just some organisation and an interest in mechanics will get you there. If you like mechanics, you should like carbs.
It's not like injection systems never fail, and when they do, there’s not much you can do with your toolbox, even less by the side of the road. It's more likely you’ll be stuck... I find that carbs are much more robust than FI systems, their sensors and the fuel pump. Dirty fuel is more of a threat to injectors because they work with minute clearances, and any change in the clearance can cause them to operate incorrectly. Injectors can get clogged (fuel residue build-up, dirt) and injection pump can give problems. Quite often injectors are sealed units, so you can’t repair them, and in this case mechanics just replace them (and they are not cheap...). And of course the computer can fail, the sensors or their wiring can fail. All sorts of sensors are needed to monitor FI systems, sensors to measure airflow, air temperature/pressure, throttle position, engine rpm, fuel pressure and so on. It is worth adding here that new cars have many problems due to failing sensors. It's likely to be the case with motorcycles too as the number of sensors continues to increase.
With carbs, on the other hand, you are in control, and personally, because I like to be as much in control as I can, and carburettors don't scare me, I would rather have a carburettor than a FI system. When a carb goes wrong it start running poorly but it won't leave you stranded... If I were to look for a bike to do some touring on, like crossing continents, it certainly would be on a carburetted bike (if they haven't been banned on our road by the time I get to do this trip!). To illustrate my point, a friend of mine in Africa needed to take the FI system out of his Toyota Hiace van and put carbs on because he had too many problems with his FI system. And he found that no one could repair his fuel injection system successfully!!
All this makes me think about something that has little to do with carbs, but rather with how fast we are loosing control over our vehicles. And this has been so much the case with cars, and it all happened so quickly we didn't realise anything. With the newest cars, to mention one of many examples, it is now necessary to give the car computer a specific command so that it can release the brake pad pin!! In other words, we can no longer change brake pads ourselves unless we invest in some serious piece of dealer software… It makes me wonder what part of taking out a pin was so difficult that the computer has to do it for us now!? Personally I see this as useless progress, and a bit scary because it prevents us from doing things ourselves... Sometimes even dealers can't do things themselves and need to be connected to the manufacturer´s website to check the car computer online. Small independent garages are having more and more difficulties to survive. Although this is another issue altogether, similar developments are taking place in the motorcycle industry, and in my view, it is not all positive...
Anyway, as electronics are getting cheaper, and for the sake of convenience, motorcycle manufacturers will soon fit their smallest and cheapest models with FI too, but I am sure going to miss carburettors, my trustworthy old friends.
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The spirit of a motorcyclist is what matters. It doesn't lie in an image or in the power of an engine. Two-wheel fun is an option for everyone, and is hard to beat.
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