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For example, in regular cars if a exhaust’s part should be detached, the problem created will not be so serious: you could have an increase in noise and pollution, but at the end your performance wouldn’t be so much affected. That’s because cars have special valves to manage fuel entry and exit. Kart engine, on the other hand, has
simple holes on the cylinder which are always open... so you can
imagine what could happen without exhaust: fuel would enter from
one side and would go out to the other side. At least a large fuel
percentage would be wasted and probably the engine wouldn’t
start up. The exhaust task is almost this one: with a particular
shape (the internal one is different than the external one) it creates
some depressions and pressures which keep the fuel inside and let
exhausted gases going out at the right moment.
Actually the real exhaust shape is this one (at least concerning the 100 category, while in the 125 category the internal and the external shape are the same): so, while for the first and for the central part the internal shape is the same than the external one, for the last part it is convergent (blue line). So the exhaust is composed by a cylindrical part fixed at the exhaust pipe exit of the engine, through a special small spiral cylinder, a divergent segment, a cylindrical segment, a final convergent segment, at the end of it a silencer is connected (partially it is internal and partially it is external). The divergent segment, thanks to a depression, increases the fuel request and so favours the entry of a bigger fuel quantity (if you compare it to a fuel entry without exhaust). The convergent segment creates a pressure (after some seconds the divergent segment has created a depression) which helps in keeping more fresh petroil inside the cylinder, in order not to have a fuel waste (at least as minimum as possible). So, while the divergent segment favours the suction, the convergent segment works at the end of the suction and creates a kind of obstacle to the fuel to be lost. This theoretical part about exhaust
was just useful to give you a general understanding of what is its
structure and how it works. Giving you more details would be almost
useless, since it would mean explaining a lot of things completely
out the kart driver concrete life.
The exhaust setting up regulation is just one: take a ruler and insert it (leant to the exhaust) until the end, inside the hollow part where there’s the engine and where the exhaust pipe starts (picture n.2), in a way the ruler leans really to the end. Then extend the ruler until the first exhaust welding (in the picture n.1 there’s the number 1 put on it); this is the measure you have to take into account. The length of this part basically depends on the engine you have on your kart. My Italsystem one is between 39,5 cm and 40,5 cm. Anyhow the variation is only 1 cm in all engines. Once you measured it, the question
is: what is the purpose of it and how can it be modified? Let’s
start talking about this last aspect, the modification. You have
to operate on a flexible spiral pipe: looking at what pipe you have,
you can eliminate some spirals or buy a shorter one. And to lengthen?
Obviously you cannot, so you should by a long one and then cut it.
Or you could buy a long one, a medium one and a short one, so that
you have all availabilities based on your need. The price of this
part is not too high. Then remove springs from your manifold (picture
n.3) as you want (there are people using the screwdriver, others
some pliers, or specific tools which are kind of screwdrivers U
shape curved at the end), remove the exhaust and the flexible pipe.
Now you can operate as you want (you can cut the old pipe, replace
it, …) and modify it based on your need. Needs generally are:
in speed tracks it’s better having a shorter length, in slow
tracks a longer one. That’s because lengthening the lenght
of your exhaust, the maximum power will be reached at a lower rpm,
while shortening it the maximum power will be reached at a high
rpm.
The needed exhaust maintenance is almost simple and fast. Basically it consists of the cleaning, the manifold springs check and the flexible pipe check. With the word cleaning, I don’t
mean cleaning it externally and having it shining (of course the
kart will have a better “look” and will not run the
risk of being dirty every time you touch it..) but I mean the internal
cleaning, because using it there’s an incrustation problem.
I was saying it’s a very easy operation, in fact almost all
people know how to perform it, and it can be divided in 2 parts:
1) The exhaust has to be warmed up and it has to reach high temperature; you can use an oxydrogen blowpipe, or a fireplace or other methods. 2) At the end of this operation (or
if you want, during it), you have to hit the exhaust to let all
incrustations falling down. These hits have to be given both from
the long side (keeping the exhaust, for example, from the top part
and hitting the part towards the ground) and on the cylinder (with
a rubber/plastic hammer for example): these hits do not have to
be too strong (or you could damage the exhaust itself) but anyhow
enough strong in order to detach the incrustations. You will not
going to find big rubbles, generally very small and pulverized rubbles
will go out. It’s very important working and cleaning when
the exhaust is still warm. This operation is very important for your kart performance: in fact if the exhaust is dirty, your performance can fall down when you increase the kart speed, since we see how much important is the exhaust system in two-stroke kart engines. Other important things to be checked are springs; at least they have to be 3. The maximum number of springs you can insert is 6. Generally 4 is the right choice; it’s important all of them work properly, with the right degree of tension. Together with the springs check, you have to check the flexible pipe too. You have to check it is properly inserted in the engine exit part and in the exhaust entry part. In addition to this, you have to check the condition: after a long use it’s better replacing it, in particular if it’s completely black, with some holes and seems to be close to fall down. In fact it couldn’t work properly (maybe it could leave too many spaces open, it couldn’t be enough flexible, very incrustated ...and so on…). Springs and flexible pipe are connected
in this way: where the part going out the engine and the exhaust
are connected, you could notice an oil leakage when the engine is
running. This fact could happen whatever the rpm is (even if I personally
notice it only at low rpm, because I start up the kart on the carriage,
where the kart is at low rpm). An oil leakage is normal if limited,
but if it is excessive there’s a problem. Together with the
oil some smoke can exit. Follow the same rule. In order of knowing
which is the correct amount of smoke and oil, you can simply compare
your kart with the others’ one. We can conclude with the ending
part of the exhaust (to follow a logical path): in the picture we
can see this part. The silencer doesn’t need any particular
care (just remember to clean also the small hole). What you really
need to check are the 2 small springs: also these springs have to
be very tightened, so that the exhaust doesn’t “jump”.
Another thing to check is a small pad under the exhaust; it doesn’t
have to be too much in bad conditions. For this purpose, you don’t
have to tighten too much the screw under it, also because this operation
isn’t useful for anything. Finally, you will see there are
2 holes, be sure to choose the most suitable one for the exhaust,
these 2 holes are at the exit of the engine; the exhaust part of
the engine requires the exhaust on the same line of the final part.
There’s a certain tolerance angle, but if it’s exaggerated
the exhaust will be linked to the exit engine part in an incorrect
way, causing a worse exhaust setting up functioning. For this purpose,
you have to choose the hole which better let the exhaust entering
in the final part: the less the flexible pipe bows and the better
is (the exposure distances of the flexible pipe should be, in front
and at the back, as close as possible).
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