Choose the language.
Tkart magazine

Special | 30 years of float bowl carburettors, with 9 models and 3 solutions… Extreme!

3
Exclusive Content

30 YEARS OF FLOAT BOWL CARBURETTORS, WITH 9 MODELS AND 3 SOLUTIONS… EXTREME!

22 February 2022
alt

A unique journey, in a world that no longer exists, that of carburettors for shifter karts. When, however, you could “get your hands on” them and the only limitations in the changes and improvements were solely dictated by the inventiveness and the level of competence of those who worked on them. Fasten your seat belts, because considering 1,800 Euro models and hybrid solutions, you will see some interesting things

History in a drawer

On the occasion of our visit to Alessandro Piccini’s workshop (read the article “Once in a lifetime – Visit to Alessandro Piccini’s dream workshop“), we were allowed to browse the drawers of the various work benches. Precisely in one of these we found a sort of mini carburettor museum, a maniacally organised space, containing carburettors of various brands and models, the result of years of work in which the carburettors were a component of karts on which trainers and drivers could express all their inventiveness in terms of development.

There was a time when the regulations did not impose particular limitations and made it possible to find the winning trick for each kart component. A time when inventiveness and flair, failures and successes walked arm in arm on kart tracks. At that time, the carburettor was one of the main areas of conquest for the preparers, a small laboratory capable of bringng joy and, at the same time, frustration. This is why, thanks to a very special selection of carburettors, we take a trip into the past and into the very essence of this sport. When in the workshops, with the shutters down, among grease, beers and machinery of all kinds, there was omly one goal: to find a way to go faster than everyone else. Without YouTube tutorials to watch or Facebook groups to question, relying on only three things: inventiveness, dexterity and … The desire to win.

A world… that is lost

We could not miss the opportunity to tell you about these jewels of the past and to do so we let ourselves be guided by Alessandro Piccini, who needs no introduction in our world: 4 world titles and official driver of some of the teams that have made the history of karting. His love for motorsport and his desire to leave nothing to chance when it comes to racing have led him, over the years, to use and collect different models of carburettors and on these to prepare every possible improvement in order to always extract the maximum from his vehicle. Thanks to his stories, anecdotes and technical knowledge, we retraced the history of a handful of carburettors that we discovered in his “kingdom”.

Our guide
alt

DELLORTO, MIKUNI, KEIHIN: we cannot talk about float carburettors (to learn more about this topic read “Technique – The float bowl carburettor”) without mentioning some of the main brands in this sector. This journey gave us the opportunity to experience first-hand the development of these components and the ways in which they were “processed”. Between interventions on the Venturi duct, on the volume of the float chamber and holes in the carburettor body, this dossier is a journey into the very essence of kart drivers. In fact, the carburettors examined are not representative of the most important and epochal technical-evolutionary steps of this fundamental component but are the plastic representation of what a kart driver is: a person who, despite having to do with the simplest vehicle in the motorsport field, continues to experiment, modify, look for a hundredth of improvement in lap time. And these carburettors show the signs of these experiments, of this continuous and incessant search for improvement typical of motorsport.

The protagonists
alt

MAGNESIUM MIKUNI KOGYO 35

Our journey starts from this float chamber carburettor by the Mikuni Corporation, a Japanese company known mainly for the research and development of fuel systems and fuel pumps, which kart enthusiasts know best for their carburettors and diaphragm pumps. Today the distribution of Mikuni carburettors is very limited, due to the DELLORTO monopoly and very restrictive technical regulations, although in substance we are talking about small masterpieces of carburetion.

Manufactured in the period 1981-83, this carburettor model was dedicated exclusively to racing. In particular, it was designed to equip the 2-stroke grand prix motorcycles, the Suzuki RG 500 XR 40, 4 cylinders with rotary valve (4 carburettors, two right and two left), of Team Gallina, winner of the 1981 MotoGP world title with Marco Lucchinelli. Its characteristics, however, made it versatile and also suitable for smaller displacement motorcycles, such as the 125 cc or 250 cc grand prix. Conceived, designed and built for motorcycling excellence (where weight reduction immediately translates into greater agility and performance), this Mikuni Kogyo had to combine the highest standards in terms of performance and the lowest weight levels, so the selected construction material was magnesium. From a traditional aspect, its real peculiarity is precisely that of being made entirely of magnesium, including the float bowl. This peculiarity, for the more experienced, can be seen directly by the naked eye thanks to its unmistakable golden colour, due to the treatment with a particular type of acid which on the one hand stops the oxidation processes to which magnesium is subject and on the other contrasts its high microporosity (which weakens its structure), extending its life-cycle. Transferred to karting, since the carburettors were not manufactured specifically for this category, this Mikuni replaced its aluminium counterpart, thus allowing an overall saving in terms of vehicle weight. The following were the engines it was most often combined with: the single-cylinder 125 Mac Minarelli, Asco, Villa and Rotax with gearbox.

Historical context

The Mikuni Kogyo 35 made of magnesium does not have any identification marks on its body. However, we know that the Mikuni Corporation usually uses the letters VM for its round valve carburettors, with this structure (the letter V stands for round guillotine and M for the type of body that must work vertically and with the guillotine operated directly from the cable) followed by the diameter dimension in millimetres. There are no abbreviations on the body of this carburettor to recognise it with precision. The impression that this model gives, at first glance, is that it is very compact, perhaps a little squat. However, let’s not forget that we are dealing with a diameter of 35 mm, much larger than the current ones used in the KZ class. The fact that it has a diameter like this and overall small dimensions is due to the fact that it was made for motorcycling where the dimensions had to be reduced to the bare minimum. It is easy to understand that, in order to maintain a resistant structure, there was little room to go further with the diameter of the duct, because looking at the rear part that is inserted into the intake manifold, we notice how much the thickness of the connection is reduced to a minimum. Its duct has a cylindrical section, with a real diameter of 34.9 mm, and mounts a traditional round valve combined with a yellow plastic ring nut and a starter kit with short clip, less practical than the lever one used today. but still very easy to use and contained in size. We are unable to measure the original external inlet on the intake side since it has been modified and brought to 63 mm, for use strictly without a filter as required at the time in the racing field. This model was made in two versions, a “right” and a “left” to ensure that it worked correctly when cornering, when the bike remained leaning and it was necessary to allow the normal oscillation of the float inside the tank. In fact, the float was connected via the balance wheel laterally with respect to the central axis of the carburettor. The two versions also had different petrol inlets positioned with respect to the intake on the right or left side in such a way as to always remain facing forward.

How it’s made

Thanks to this carburettor, Alessandro Piccini retraces the first years of his career, which began almost for fun (for further information, read “Editorial – Alessandro Piccini: from 40 in karts“) “This 35 mm Mikuni Kogyo was an absolutely performing carburettor from all points of view: it allowed a greater range of use than other carburettors popular at the time and had a fairly good delivery response in relation to its short length despite a round and not flat guillotine. The initial diameter was 35 mm, but sometimes it was enlarged, even if the available thickness was really reduced”. With the help, and several suggestions, from excellent trainers, Alessandro immediately began to modify this carburettor in various aspects, including, for example, a very important Venturi flange, created on a lathe and then mounted for interference. However, Alessandro tells us that this modification, which we have noticed, is the latest in a long series since “it was very difficult to find the best radii without spending hours on the flowmeter which at the time was not so close at hand, we needed a lot of evidence”. In fact the changes, mainly took place due to study, specific knowledge and a lot of experience. If we analyse it carefully, we notice that it has even gone in the opposite direction to what the vast majority of enthusiasts would think: the inlet diameter has even been reduced to 30 mm, with a very precise radius, both in the front and in the one at the rear of the aluminium flange, which however we were unable to measure. This allowed greater stress on the pulverizer (soiled pulverizer), with better performance over the entire range of use of a kart engine.

Alessandro's anecdotes
alt
Continue reading the article by subscribing for only € 0.96 / week