If we should decide which part has the “priority” and which aspect or regulation is so important to put a lot of attention relating to a kart, they would be the carburetor and the carburetion. The carburetion is something very difficult to understand, also for expert people. During world championship you can see pilots who seize, since they have an incorrect carburetion (even if during that kind of competition all engines are very close to their max feasible performance); this fact confirm it’s not so easy finding the right carburetion and regulating it. In fact an incorrect carburetion is the most frequent cause of engine malfunction or breaking. When something is not running correctly in your engine, very often there’s something wrong with the carburetor. So the carburetion is the main factor to be considered in karting.

WHAT CARBURETOR IS AND HOW IT WORKS

The carburetor can be defined as part of the engine, responsible of engine feeding. It means it is the tool responsible to mix fuel and air and to put the petroil in the engine. The carburetor has a quite big dimension (it means if you keep it in your hands you can perceive a certain satisfaction) and inside it is very complex how it works. Here you can see again a picture of it (made smaller).

This is a carburetor for 100 category; in the top of it, there’s a plastic part where the fuel pipe is inserted, and it goes to a covered small tank inside the round plastic part. Through a not easy way, the fuel “falls” in the big hole (you can see it in the picture), it goes through the whole carburetor, and from there it enters the engine together with the air, which is sucked in thanks to the depression created by the piston going up in the carter. The pipe is almost closed by a valve (usually it is a choke butterfly plate). The more you accelerate, the more the wire is pulled and let the valve open. In this way, being the surface bigger, more air and fuel can pass and the speed increases. On the carburetor there are 2 (in some cases 3) "screws", used for the carburetor regulation, which is the most interesting aspect. The carburetor price is not lower than 130 euro, but it depends on functionality, brand and quality.

CARBURETION REGULATION

This is the most interesting and important thing related to carburetor; and the basic concepts are the following.

The carburetor regulates stoichiometric ratio, that means the ratio air/fuel. This ratio should be around 14,5 - 15. Lower ratios define greasy carburation, while higher ratios a lean carburation.

The carburetion can be regulated in 2 directions, or you increase the fuel percentage (in comparison with the air – greasy carburation) or you increase the air percentage.

To have a greasier carburation screws have to be unscrewed, to have the opposite you have to screw all screws.

Let’s start saying a greasy carburation can be harmful, but a lean one can be very very harmful: in the first case the engine run the risk of being flooded, in the second one it runs the risk of being seized, which is even worse… From here, we can resume 3 main rules:

Rule number 1: if you are undecided about which direction to follow, you can increase the fuel part with no worries, but if you want to increase the air part… do that with a lot of care and not too much.

Rule number 2: the carburetion has to be revised very often. Once you have found the right carburetion, you can keep it until the end of the day, not more. In fact regulations, which are fine with certain ratios (even if it’s not so important) and under certain weather conditions (rain-sun, warm–cold, dry-humid), cannot be used for the next time. You can keep the last regulation as a starting point for the new one.

Rule number 3: do not regulate the carburetion when the engine is cold. You have to warm up the engine, going very slow for some laps and then regulate it.

In order of regulating the carburetion, you can follow this procedure: put the kart in the track, regulate the MIN screw at one opening round (starting from all close) and the MAX one at 1 and 1/4 and the power jet at 1 round and 1/4. These settings are ok for all carburetors and engines, but they have to be kept as not more than starting point. The MIN screw can be less open only to facilitate the kart start (if your petroil has a higher percentage of air, the kart will start easily…. closing more the screw is more difficult..); but after the starting up, it’s better opening a further ¼ round (be careful not to confuse the rotation way when you are on the kart, since you’ve changed your position). Drive slow some laps: it will smoke even if there’s a high air percentage because the engine is cold (the oil burns worse than under normal conditions). Now we can start explaining regulations.

First of all you have to regulate the MIN. The MIN is the main responsible of the engine behaviour when it is at low rate. The screw responsible for its regulation is the most internal one, very close to the engine. To regulate it, you have to bring the kart to a low rate, but remember the kart starts up around 6000 rpm, so you cannot have it lower. At this point you have to accelerate with a clean blow. And here you can study the kart reaction: if it’s well carbureted the response is high, the acceleration is sharp, sudden and “nervous”; based on the kart grip and position, your kart could powerfully give gas (for example during bending in a track with not too much grip). Very likely when you execute this operation, your kart won’t be very well carbureted and so the reaction will be caused by a “hole” in which the kart will slowly raise speed for a long period of time; after it, it will start running better. This reaction doesn’t say anything about petroil (if it’s greasy or not; even if very often is greasy) since the hole can be caused by the lack of fuel (in this case the carburetion would be very lean), or by an overabundance of fuel, which doesn’t favour a good combustion. At this point, for safety reasons, it’s better greasing and seeing how it’s the reaction. If the reaction it’s better than before, that’s a good sign and you can grease a bit more, until you continue having good performance. If it’s worse, the petroil is really grease; in order of being sure of it (without running the risk to seize) try to grease, opening the MAX screw; if it doesn’t improve you can be sure the petroil is too grease. Then return the MAX screw in the previous position and subsequently close the MIN one (let’s say you should close it of almost ¾ from the starting position, which is a “completely close” position). Turning for a while the screw in the 2 directions, you should find the right position. On the contrary, continue attempting and when it seems you have found the correct carburetion, stop and keep in mind how the screw is regulated, then close it and count turns (or fractions of turn) you need to close it completely (we are talking about the MIN screw). If it’s open a lot (‘til 1 turn and 1/2 - 1 turn and 3/4), it could be ok; if it’s too much close (less than 3/4) it could be dangerous. It could even be the correct regulation, but you enter the track with a petroil with too much air, which is very dangerous for your engine. It could even be you need to revise the carburetor. Anyhow, since I don’t have any other advices to give you, I really hope you have the MIN well regulated.

We now have to see how is the kart behaviour at medium speed (around 11-12-13 thousand rpm), which should be the moment when you have the best performance; that’s the situation your kart has the maximum power and the best torque. Considering that your MIN screw is almost at the right regulation, you have to act on the MAX one, and then slightly revise the MIN one. The test is always the same: you have to reach that speed, driving in a constant way, then suddenly accelerate and you should wait for a fast kart response. If the response is not as expected, the solution is the same we said before but using 2 screws. In case of not optimal reaction, you have to grease the MAX screw (the external one), then try to do the opposite (if you didn’t get what you wanted greasing) and, in this case grease once again the MAX and regulate again the MIN in the same direction. At the end, in “disperate” situations, lean both, being very careful not to get close to the “danger level”, even with just one screw. At the end of this regulation, test the MIN response at low speed, then test again at medium speed. If you are not able the get a good regulation for both, you can follow a kind of criteria which links the carburetion regulation to the track type (even if in a very approximate way). If the track is full of slow bends, low speed is the best choice; if it’s full of medium-fast bends, medium speed/rate has to be chosen. Anyhow if you should have this problem (that you cannot regulate your carburetion at each speed), probably you need to completely revise your carburetor (it could also be the engine, but more likely the problem is the carburetor).

Assuming everything done until now is ok, we can start in regulating carburetion at maximum speed (I don’t know if it’s the most difficult or easiest thing…). Considering I don’t have a power jet screw carburetor, I dont’ have a direct knowledge about it; anyhow it’s not very popular and the action you should perform is the same one you did for the MAX screw – as I’m now going to explain - (the power jet screw is the most external one, not in line with all the others… in a weird position). Run your kart to very high rate (not less than 15.000 rpm) and simply, during the fastest straight stretch, stretch and challenge your kart performance (exploiting also a good going out from the bend, before entering the straight stretch). You should reach the maximum rpm. Unfortunately it depends more on ratio than on carburetion, but these two things are a bit depending on each other. To realize it, you should notice something during progression: if engine is overworked and it seems to push “without determination” and maybe utters not a clear noise, (combustion is not as it should be), petroil should be a bit grease. Instead, if your engine has a good running performance but not an optimal one, it seems to be overworked (the engine is keeping a certain speed but with a lot of effort) and it utters a metallic noise, try to cover the filter with your hand, because in these cases the reason could be a lean petroil, and at this rate you run the risk of seizing. So drive slowly your kart for one lap, to give the engine the possibility of “relaxing”,… after a long filter coverage by hand, leave it uncovered. In the first case try to lean a bit, in the second one grease a lot. I hope you were able to find the correct carburetion, on the contrary act as follows (kind of comparison method): in fact you should grease and see how things change, then put the regulation as it was before, then lean and see again the reaction (very carefully here…). Going on with these tries, you should understand which kind of carburetion you have and how much it is in one direction or in another.

Then try again at all different speeds, and eventually slightly revise all regulations in order to find the ideal setting.

1st IMPORTANT REMARK: If you corrected a grease petroil to have a lean one, you should wait a moment before testing new setting result: in fact the sparking plug is probably wet and it’s necessary covering a certain distance to “clean it”.

2nd IMPORTANT REMARK: Avoid to test the carburetion regulation on the carriage, even the low rate one. This test is useless, since the behaviour of your kart when it’s in contact with the ground is completely different. Avoid to reach a high rate/speed when the kart is on the carriage; keep it always at low rate.

3rd IMPORTANT REMARK: All advices I gave concerning regulation are quite general; actually you should be informed about settings for your specific engine together with carburetor: difference can be very broad. In some case you could go below 3/4 turn (anyhow not too much), if this 3/4 is the basic setting. So, if the basic setting is 1 and ¼, it’s very dangerous going below 1 turn and so on. Actually the only real test is driving… and since at the beginning you are not an expert, you have to practise by errors. But it’s always better not incur in very serious mistakes, so grease a lot but leant very carefully.

4th IMPORTANT REMARK: Before regulating the low rate/speed, it’s better driving very fast; it’s very important because on the other hand you could have your kart with a wet sparking plug and the regulation would result impossible.

General advice concerning carburetor and its use

Before going fast with your kart, during warm up, it’s advisable squeezing (with 2 fingers) the pipe which brings petroil to the carburetor. In this way petroil will be leaner and at low rate the sparking plug will not be wet. For the same purpose and in order to clean the sparking plug, it’s also sometimes advisable accelerate.
At the end of the day, it’s better if you empty the carburetor and remove any petroil trace from the carburetor (especially if it is unleaded), since the carburetor could be ruined. I don’t know if it’s true, but it’s better not running this risk: in fact it takes you just 5 minutes to clean the carburetor and other 5 minutes to fuel your kart. So it’s up to you deciding, based on time, possibility and will. To easily clean the carburetor, it’s enough to put some compressed air (not too strong, let’s say not above the bar and half), where there’s the petroil entry neck for some seconds.

Revising the carburetor is a very easy action. It’s more difficult explaining it than performing it (since now I don’t’ have in front of me the part: you just have to disassemble the cover-tank and the underlying part, which is fixed by small allen screws. Once you opened it, you can act with a compressed air pistol (always with a low pressure) to clean everything (in all small holes) and then check membranes, and based on their condition, you can decide to replace them (the cost of it can be around 25 euro). Also spilli (regulation screws) have to be disassembled, then they have to be cleaned and you have to clean also the hole where they are put; regarding spilli, you have to check 2 rubber rings and if they are ruined, they have to be replaced. You have to check the internal spring (it’s very easy to recognize it), since if it’s very worn out (and it becomes less hard than when it’s new or than you want), it has to be replaced, too. After cleaning the whole carburetor, you can reassemble and test it.

Regarding the internal spring hardness (which regulates the petrol decent): if the valve is quite hard you will get a lean petroil, if it is quite slack, the petroil will be the opposite. For enthusiasts and not very expert people, it’s advisable choosing quite slack springs. Also the spring hardness (so if it’s hard) could be the cause of seizing, in particular if you are in a track which has a kind of straight stretch - speed bend series and with a wide radium - straight stretch: in fact we can say a slack spring works as a container of a small petrol quantity, which is released in case of holes due to shifting (in this case the shifting is due to the kart side acceleration during bending); with a hard spring you run the risk of having a moment when the petrol cannot enter and so the temperature raises a lot, and at the end of the straight stretch you could have a engine seizing. A slack spring is not really a container, but considering it like a container, it’s very easy explaining why a lean petroil (due to a hard spring) cannot always be balanced by a petroil greasing done by an action through regulation screws.

Air filter

The cost of an air filter can vary between 25 and 80 euro, even if I’m not very convinced there are a lot of quality differences between air filters, since this component is so simple. If we look at the air filter in the picture, air entry holes are lateral and I think in this position they are quite difficult to be closed in case of need.

First of all I want to say the word “filter” is not a fitting one; in fact this plastic part is completely empty inside it and it doesn’t have any kind of “defences” against external agents. Its purpose is to reduce the risk (or to increase the safety, it depends on what you mean, but I prefer the “risk” concept): in fact instead of leaving the carburetor completely free of sucking in everything, it limits the air entry in 2 small holes, which could be on the front part or on the side (as shown in the picture). The simplicity is due to the fact in karting there are competition engines which require the entry of a lot of air and every filtering element would be a kind of obstacle, with a decrease in performance.

One side of the filter is directly connected to the engine, while the other one is completely free; it could be lifted up if the air pushed it from below: for this reason in the top part there’s a kind of fin which pushes the air filter down. If you should run into the opposite problem, it means the carburetor is too pressed, you can make a small hole in the bumper, on the engine side where the front part of the air filter is put (in this point it should have a small hole); then bind the filter with a small band, which is easily removed by scissors.

The filter is connected to the engine by a small band; this band has to be quite tightened but not too much…, or you will run the risk of ruining the filter itself and creating cuts and cracks.

The only maintenance needed is simple but very important: the cleaning while it is really needed.
In particular when you finish using it, but in every situation you need to clean it, do it, removing both dirtiness coming from outside and petroil residues, which are lost by the carburetor. Most of all, it has to be removed any water as consequence of a wet track “exit” or as consequence of driving under rainy condition (if there’s water inside the filter, the engine will be negatively affected in a very heavy way); in particular you have to remove all pebbles and other small and hard objects which could enter the engine and cause irreparable damages (or very expansive to repair).

The filter simplifies a lot the break of the air entry into the engine; for this reason a small trick exists and it consists in closing with your hand the filter at the end of a very speedy straight stretch, so that the engine can continue working with a lot of fuel but almost without air, so that the temperature can be lowered in order of avoiding engine seizing. The action of covering the filter has to be fast and minimum, on the other hand you will risk not to have enough power to exit the bend (since the engine, from a certain point of view, has to start again) and then also to wet the sparking plug (with a drop in performance). Some years ago there was a kind of story which said this trick was invented by Ayrton Senna and it was used to have more fuel to burn at the end of the bend, in order of achieving a kind of “turbo” effect; actually it’s a story which let you smiling, but it was like a tale between people…. I would advice the purchase of a filter with holes in the front part instead of lateral because, from my point of view, it’s easier to be covered by your hand.