Do-it-yourself Java tuning - new motorcycle capabilities

The legendary Java 350 motorcycle is the dream of every motorcyclist of the late 20th century. Not a single Soviet motorcycle could compare with the quality of workmanship and smooth running of the Java. The particular popularity of Czechoslovakian technology is still relevant today. Naturally, every owner wants to improve the characteristics of the model, and the topic of today's article is Java tuning. In it we will look at what Java 638 tuning is, how to achieve better performance from the engine and create a modern appearance with your own hands. Let's find out how the Java 634 tuning differs from the 638 model and which is better.

Tuning Java 350 let's start with the engine. Clean the engine thoroughly from dust and oil to prevent dirt from getting into the engine. Having completely disassembled the engine, carry out a complete inspection for wear. It is recommended to immediately replace the bearings with new Japanese ones, since only they can cope with the increased speed and increased power when tuning the engine. Keep in mind that boosting the motor is a serious matter; at least turning, a grinding tool, and preferably a drill to change the purge channels will be required. The factory shape of the channels provides traction at low and medium speeds, which is done in order to save fuel. By slightly boring the cylinder bores a few millimeters in height, you can increase the engine speed and, accordingly, its power. To improve purging, be sure to align the channels of the lower plane of the cylinder with the upper plane of the crankcase; steps and protrusions that will interfere with the flow are not allowed. Also sand down any irregularities in the intake and exhaust ports until they are smooth. Then we move on to tuning Java 638 cylinder heads. To do this, having secured the heads in a lathe using a mandrel, cut them with a cutter by 1.5-2 mm, due to which the combustion chambers will decrease and the compression ratio will increase. If you have a Java 634, tuning the pistons consists of making them lighter; to do this, the jumpers of the lower piston skirt are cut off, and the free space under the piston will ensure the unhindered flow of the fuel mixture. Tuning Java 638 is more preferable because it has aluminum cylinders that can withstand boost much better and effectively remove heat.

The power supply system is very important for a two-stroke motorcycle. The filling of the cylinders and power depend on the quality of mixing of fuel with air. Reed valves also play a huge role in this system. It allows the fuel mixture to be admitted when the piston is sucked in, and does not allow the mixture to be pushed back, thereby improving engine performance. Reed valves can be selected from any other two-stroke motorcycle of similar capacity. A photo example is shown below:

The efficiency of tuning Java 638 can be significantly increased by dividing the intake channels into two separate ones for each cylinder with its own carburetor.

One standard carburetor is not able to fully cope with its task and significantly chokes the engine in terms of speed. Installing crossover carburetors from Mikuni or Keihin with a diffuser size of 28mm will radically change the behavior of the engine. You can read how to set up a Java carburetor here.

Bright, stylish, but still Dnepr

Looking at this motorcycle, different emotions immediately appear in me. On the one hand, the author of the project had a hand and spent a lot of time creating this “horse”, but on the other hand, I don’t see much point in them. It is unlikely that this homemade seat will be more comfortable than the standard one.

Exhaust

- the highlight of the whole design. As for me, the “cans” are too massive for the pipes that go directly to the cylinders. I think if they were made thicker in cross-section, this modification would look somewhat more impressive.

The colors here are extremely bright and dull

, but this is
a matter of taste
. And, according to the classics of the genre, we are witnessing the abandonment of the steering wheel and the fact that the author of the project gave preference to clip-ons, completely cutting down the ability to move around on this motorcycle.

Java engine tuning

First of all, I would like to talk about modernizing the engine of this once legendary bike. The latter is done quite easily and quickly these days. The method of strengthening the power unit, given to us by our parents, will remain virtually unchanged. These motorcycles are quite easy to boost.

Tuning Java often involves adding another carburetor to the engine. In this case, the mounting of the basic fuel regulator is subject to change. A carburetor is installed on each cylinder only after a new mount (adapter) is installed on each “pot”. All this is mounted on pins - there is no need to invent anything new, as you can see for yourself. Each carburetor needs a separate filter. Buying a faucet for a tank with a couple of outlets is also not difficult.

Firstly, you need to adjust the purge channels for tuning the Java 350. In addition, the main goal of upgrading the Java engine is to increase the compression ratio. This way you can certainly supplement the power of the bike. All this won't cost that much. If you do not have the necessary tools and equipment for speeding up, you can turn to a turner. Even in small towns, such specialists are present, for which we must thank, first of all, the Soviet government, which relied on the engineering and mechanical potential of the labor resources of the USSR. There are many machines left on post-Soviet soil that are quite suitable for reducing the combustion chamber.

Do not forget that any changes to the combustion chamber, as well as the cylinder windows, must be carried out with the utmost care. Any mistake, in this case, can render the rather fragile duralumin “pots” unusable once and for all.

You will probably find photos of bikes after some of the above modifications here too.

MY MOTORCYCLE

Improving an engine can only be done by those who understand what is happening in it, have metalworking skills, experience working on metal-cutting machines and... patience. These qualities can, of course, be acquired with experience and in a constant process, but you can just ruin the engine. Although those who do not take risks do not drink champagne. This article is for those who do not have enough resources provided by the JAWA 350/634 engine. But be careful with forcing too: you never know...

REFINING THE CYLINDERS First of all, the engine must be thoroughly washed and completely disassembled. Check the gearbox and engine transmission parts: those. which have defects will not cope with the increased power and will fail. And if the piston group is worn out, alterations will be of no use at all. You will need files, cutters and an electric drill (or better yet, a drill). The shape and size of the purge channels of cast iron cylinders are often far from ideal, especially at the joints between the cylinders and the crankcase. The speed of the fuel-air mixture at high speeds in these places is so high that a step of just half a millimeter can cause a vortex that “eats” up to 20-30% of the flow area. In order to regain lost power, you will have to work with files and cutters and eliminate factory flaws.

How to detect discrepancies? Make gaskets from thick paper, one for each cylinder and one for the crankcase. Copy onto paper, running your finger along the back, the channel imprints of each part. Having aligned the paper prints, find a position (as far as the pins will allow) at which the channel mismatches will be minimal. Place marks, and then secure the parts with steel pins so that during subsequent assemblies they will always occupy this position. Now remove the protruding areas. Gaskets installed under the cylinders after assembly must exactly match the shape of the purge channels. Edges that protrude inward will give the same effect as mismatched channels. The angles and shape of the purge channels at the exit to the cylinder determine the direction of movement of the fuel-air mixture, and, therefore, the quality of the purge. Any arbitrary changes in these places can undo all the work. It is enough to sand all channels: inlet, outlet and purge with fine sandpaper. There is no point in polishing until it shines. Lower the lower edge of the inlet windows by 3.5 mm, and make a smooth transition in the channel (as shown in the figure).

After this, having assembled the crankcase with the central insert, adjust and polish the intake channels. Raise the upper edge of the exhaust windows by 2 mm. Make a 0.5×30″ chamfer on the upper and lower edges - this will extend the life of the piston rings. Do not touch the upper edges of the purge channels: this will significantly worsen the purge of the cylinder. There is no need to expand the entire exhaust channel; sand off the casting flaws, and near the windows, polish the surface of the channel. Much less carbon deposits are deposited on smooth walls.

General concepts of Java tuning

Improving Czechoslovakian Jawa quite often involves the installation of new electronics. In addition to the ignition system, the number of lighting devices also changes. Fog lights are installed, new indicator lights are installed on the panel, the sound signal is replaced, etc. However, the instrument panel is often left unchanged by tuning specialists for the 634 Java. This legendary Czech motorcycle already has everything that is needed to indicate the operation of the bike. The most pleasing thing is the presence of a tachometer.

Sometimes the front end of the above iron horse becomes heavier. Since a motorcycle can easily rear up (on a goat), this often infuriates many motorcycle enthusiasts. Tuning Java, in this case, makes the front structural elements heavier in any way the owner likes.

You can reduce the fuel consumption of this two-wheeler. The jet clearance in the carburetor is simply reduced. There are also many ways to carry out such modernization. In turn, along with a decrease in gasoline consumption, the power of the bike’s power unit will also decrease. The engine will become less playful, which may even benefit many lovers of comfortable driving. Some riders are annoyed by the fact that the bike tries to rush forward immediately after engaging the gear, despite the fact that the clutch is depressed.

Back
Forward

Tuning various elements

The modernization of these Czechoslovak motorcycles, as a rule, does not end with external tuning or increasing engine power. Very often, owners of these motorcycles install additional electronic equipment and replace some standard parts. The first thing to do is change the standard ignition system, especially if we are talking about a motorcycle with a “bored” engine. Optics and various lighting equipment are also subject to changes - new headlights, foglights, different front panel lighting, etc. are installed.

The brake system also needs some modifications, usually replacing drums with disc brakes. Sometimes it is recommended to weight the front of the motorcycle. This can be done in several ways, both with your own hands and with the help of specialists. It is worth noting that if you do not have the necessary knowledge and experience, it is better to resort to the services of tuners, since motorcycle owners often make serious design errors when independently upgrading the engine and other elements of the motorcycle, which subsequently leads to emergency situations on the road.

What can be tuned in Dnepr?

At the time these motorcycles were released, their quality was at the highest level, so all the components and the design itself still actively serve all owners. But modern requirements for appearance and some technical characteristics force us to carry out cosmetic and internal modifications to the motorcycle. Of course, you can do the tuning of the Dnieper with your own hands, but if you don’t have enough knowledge, workshops are open in most cities where people are probably knowledgeable in modernizing Soviet motorcycles.

There are basic elements that need to be changed when tuning, and in this model the following elements can be improved or even replaced:

exhaust pipe;
almost the entire chassis, in particular the windshield, roll bars;
engine;
front fork.

You can also briefly discuss the refinement of each element. For example, to tune the exhaust system, you will need to install a forward flow system and nickel elbows, which you can do yourself. External tuning will contain a lot of chrome parts, so tuning the Dnepr engine will involve a polishing process. If you upgrade these two parts, your motorcycle will not only look great, but it will also sound great.

As for technical modernization, the above recommendations can be supplemented by installing a fifth gear on the Dnepr. It is unlikely that you will be able to do this kind of work yourself, so it is better to turn to specialists with experience. But the result will be justified; your vehicle will have reverse gear. But even this is not where the basic tuning ends, because some Dnepr models, depending on the year of manufacture, can be improved by installing an electric starter.

Technical and operational characteristics of jawa 350 638

Jawa 350 638 has the following technical characteristics:

The fuel consumption of the Java 350 638 motorcycle is about 6-7 liters per hundred, which is a pretty good indicator for this class of motorcycle of that time, because only Japanese motorcycles, which are much more expensive, gave similar results.

Smooth running was achieved by a 4-speed gearbox consisting of three main shafts. The steering function was a conventional Java 638 telescopic fork. The electrical circuit of the motorcycle is based on a 12V circuit. Generator Java 638 with a power of 210 W, at 14V and 15A at 5000 rpm.

The Java 638 carburetor is a float carburetor with a central chamber equipped with a device for easy engine starting. When operating a motorcycle, it is necessary to pay due attention to the Java 638 crankshaft, because due to insufficient lubrication, this is a rather vulnerable part of the motorcycle.

Body and frame tuning

Its appearance will largely depend on how the frame base on the motorcycle is redone. At the present stage, there are several popular ways to remake the Dnepr frame.

Regardless of the modification of this bike, all models have a similar frame design.

You can extend the frame at the rear of the motorcycle. This tuning involves adding 15-20 centimeters to the frame, which increases the space for the rider’s legs. When the frame is lengthened, the driveshaft also lengthens, and the adjustment of the distance by which the frame should be lengthened depends on the height of the driver. If you lengthen the frame in the front part, you can achieve a landing similar to classic American choppers, while you do not need to change the driveshaft, but you will have to redo the pedal arrangement.

The frame is also expanded. We are talking about installing a more powerful rear wheel. To do this, an additional gearbox is installed on the cardan shaft, which will shift the cardan output to the side. It is best to install wheels with a profile of 130-150 millimeters, this way you can achieve optimal ride quality from the bike. A tire that is too wide can add certain difficulties to the driver.

When changing the angle of the front fork, experts recommend increasing the angle of inclination by no more than 35 degrees, otherwise the handling of the motorcycle will be seriously affected. In addition, an increase in the angle of inclination is accompanied by loads on the “stays” of the front fork, which leads to their rapid wear and failure.

Changing the angle of the rear shock absorbers will provide a more aesthetically pleasing appearance for the motorcycle, however, as with the front forks, too much angle can result in a loss of load-carrying capacity to the point where even single-passenger riding becomes impossible.

Sports option

Tuning for sports, due to the technical features of Java, is the most common way of modifying it.

Basic requirements for sports motorcycles:

Maximum speed.
Acceleration speed.
Controllability.
Safety.
Convenience.

One of the obvious disadvantages of the Java 350 is considered by many to be too light a front end, which begins to lose traction at high speeds. Therefore, despite the need for a general lightweight design, when installing a sports front fork, it will not be superfluous to place a counterweight. Changes to the chassis also include the installation of disc brakes, alloy wheels and a more wear-resistant chain from IZh motorcycles.

The performance characteristics of the Java 350 are largely relevant to this day, but the modernity of its design is a big question. The simplest option for external tuning for sports is to install parts from the Yamaha FZR400 and Kawasaki KR250 on a motorcycle. The first option is an excellent donor for the front wing, the second - for wheels, front forks and brakes, rear shock absorber and pendulum.

The last part for installation in the Java socket must be narrowed by replacing the standard bearings with needle bearings from the Volga pins. The combination of these innovations makes the motorcycle more maneuverable, stable and controllable. Body kits are made to order, both in workshops and by “home” craftsmen. Do-it-yourself external tuning of Java is also not uncommon. To do this, it is enough to be attentive and careful, and also to have a sufficient amount of plastic or fiberglass with you.

Unusual yellow Java 638

Personally, I have a conflicting opinion. It is clear that the author of this project spent a lot of time on its implementation. Didn't save money, bought an exhaust with resonators

, painted the entire motorcycle in a bright and noticeable color, installed caps on the wheels. I even installed a mono shock absorber.

With all this, I have one question: why? It’s not clear why the “tail” of the motorcycle should be lifted up so much, or why install clip-ons. I think this bike will be equally “comfortable!”

both driver and passenger.
Looking at the passenger footrests, it’s difficult to imagine how two people would sit on this Java. Well, the final chord – turquoise zero
!

Of course, the author is a great fellow

, had a hand in it, but the essence of the project remains a mystery to me.

Perhaps, such Java is truly the only one in the world!

Here I can definitely say that I would like this “tuning”

did not engage in training under any circumstances. I had enough sad experiences with vinyl film, but this is still on a completely different level.

I can’t say that this solution looks beautiful, nor can I imagine what will happen to all these “carpets” after a trip in the rain.

I would put such a motorcycle at home to entertain guests, but, alas, there is no extra space. It’s strange or not that here the author of the project decided to abandon the standard steering wheel

? Who knows, maybe the motorcycle really went faster or the landing became more comfortable.

Extraordinary JAWA tuning in action!

Here, too, I simply have no words. On the one hand, most of the motorcycle is kept original - the lower part. The pipes are shiny, no oil is leaking from them, good tires are installed, the engine is clean

. Most likely, technically everything is fine with this motorcycle, but why “decorate” it like that?

I remember as a child I was perplexed when I saw motorcycles passing by, whose seats were covered with some kind of skin, carpet, fur coat or something like that. Is this really convenient?

What's wrong with standard casing? Even if it was in short supply, is it really impossible to use another, more suitable material?

Well, I’m generally silent about the fairing. The solution with lighting devices is strange, in my opinion. At the very least, very extraordinary. And yet it is not clear why he was wrapped in a rag. Probably to match the seat.

Source

Improved technical characteristics

The following steps are allowed:

replacing standard crank (crankshaft) bearings with support units of better quality, attention, without reducing the size of the journals; installation of K-301B instead of the base carburetor, with mandatory adjustment of the synchronization of its operation; cleaning the engine cylinder channels and setting the ignition timing from 40 to 42 0; installation of a pair of air filters from GAZ-24 or Moskvich-412; minimizing the weight of connecting rods and pistons - an example is removing flash - to improve engine performance; organization of inertial boost - with it, the tuned Ural will be able to reach higher speeds, but only if a high-quality and reliable compressor is selected; production of a camshaft with cams of a non-standard profile, facilitating changes in valve timing; although it is better to entrust this task to professionals; making new gearbox gears is a more than justified measure, since standard parts usually make quite a lot of noise during operation, shift relatively poorly and do not last very long; alignment, grinding, lapping of both intake and exhaust valves - to increase the efficiency of filling the cylinders with fuel.

Addition

Tuning Java 350 very often affects the exhaust system. Despite contraindications from specialists, many owners install forward flow systems made from VAZ 2131 mufflers on this motorcycle; 21213; 21214. The part of the pipe leading to the engine is cut 5 cm from the muffler itself, and the part going out is bent at the required angle. When connecting to the elbow, the pipe is slightly cut and pressed tightly. The body mount is first welded to the forward flow, and a footrest is finally mounted on the motorcycle itself.

The tachometer, often borrowed from the VAZ 2106, will add to the presentation and functionality of the unit. Its connection is made according to the same parameters as in the car. Installing a starter on a Java 350 is a rather complicated procedure, but quite realistic. It requires a flywheel change, additional mounting on the body and a reinforced battery.

Motorcycle lighting is another characteristic manifestation of sports tuning. LEDs, the color of which can either emphasize the color of the device or be in contrast with it, illuminate key design components: the engine, exhaust pipe, rims.

Correctly performed tuning can not only transform your two-wheeled friend, but also significantly improve its technical parameters, making the motorcycle the envy of surrounding motorcyclists.

https://youtube.com/watch?v=YgfNadWJd1M

Increasing the power of a 2-stroke engine

Many people believe that in order to restore the engine's former power, it is enough to replace worn parts with new ones and carefully break them in. This usually happens, but often, after completing the repair, they note with bewilderment its low efficiency and, having unsuccessfully tested various adjustment options, they conclude that it is impossible to get more from this engine. In fact, if all other systems are in good working order, very often it is possible to significantly increase the main parameters (power, throttle response, efficiency) of such a motor by fine-tuning, or rather, by mutually adjusting some of its parts.

The fact is that due to the requirements of mass production, such as the motorcycle industry, some dimensions of parts, especially those produced by casting, have a fairly significant spread. If we add to this the frequently changed casting molds, which do not always exactly repeat the previous ones, it is not difficult to imagine that inconsistencies between some parts and others in the event of an unsuccessful combination may well occur during assembly.

This discrepancy is most often observed in the cylinder and crankcase of two-stroke engines, where the channels and windows do not always completely match. This causes not only a decrease in flow areas, but also turbulence in gas flows, which worsens the charge of the mixture, and therefore the power, acceleration dynamics, and fuel consumption.

Fig.3. Scrapers for channel processing.

Let's take as an example the YAVA motorcycle engine of the “634” type. whose owners are the most demanding in terms of power (recommendations apply equally to engines of other brands).

So, we install the cylinder in the corresponding half of the crankcase. Here you can detect a discrepancy between the lower (bypass) windows of the cylinder and the beginning of the purge channels in the crankcase (Fig. 1).

Most often, there is a circumferential displacement, which it is desirable to eliminate. To do this, you have to remove metal both from the cylinder and from the wall of the channel in the crankcase. The entrance to the purge channel should be smooth, without ledges. The upper outer edge 4 of the bypass window can be rounded. Sometimes, in order to ensure an even smoother entry, the lower window bridge in the cylinder (6) and piston (5) is removed completely, and the lower edge 7 of the crankcase channel is rounded (Fig. 1.6). But such a measure can reduce the life of the piston and partially increase noise. according to our observations, slightly change the engine characteristics in favor of higher speeds. At the same time, it completely eliminates the risk of spontaneous breakage of the lower piston bridge, which, unfortunately, happens. Among experienced JAVA owners, such a piston reconstruction (Fig. 2.6) is very popular.

In conclusion

To improve the performance of their two-wheeled “iron horse” and give it a second life, many owners use tuning. “Java 350” is a quite decent motorcycle, but in design and parameters it no longer reaches modern models. Modernization allows you to make fundamental changes to the design, resulting in a car whose owner will be the envy of everyone around you.

It is quite possible to remake the equipment yourself. Properly performed restyling will not only transform the motorcycle, but also make it a unique bike. The main thing is to stock up on the necessary materials, theoretical knowledge and patience.

Previous entry Motorcycle repair and maintenance

Improved appearance and safety

Think about safety first. Standard rims, and even more so drum brakes, are not able to cope with the increased power. It is recommended to install a good disc brake along with replacing spoked rims with alloy wheels. This will not only give a modern look to your bike, but will also significantly improve stability on the track. Accordingly, improved rims from another motorcycle are designed for greater braking force and have normal mounting for the brake disc. Good road tires are also a must.

Replacing headlights and other outdated lighting equipment will appeal to everyone. And the dashboard can be easily transformed by installing LED strip lighting.

The standard steering wheel can be easily replaced with clip-ons or a straight-shaped steering wheel, which will somewhat improve the driver’s aerodynamics due to the inclined seating position. Installing wind deflectors is no longer in fashion, as in Soviet times; they create too much air resistance in front of them. Much preferable is a sports body kit, which, depending on the financial investment, can be picked up from any other motorcycle, but if you really want to make it yourself from fiberglass and epoxy resin. Tuning a Java motorcycle in the photo:

And finally, we want to say that a forced engine requires good 2-stroke oil and timely maintenance. Java tuning is a fascinating activity that requires imagination and direct hands. If you follow the tuning technology, the result will not leave you indifferent

Java is a dream motorcycle of the 70-80s of the last century. IZH, Voskhod, Minsk, even the powerful Ural, all this is not the same in comparison with the only imported motorcycle widely available to the Soviet motorist - Java. And even though this is not a bike from the decaying, but technically more developed West, but an import from a country party to the Eastern Treaty, Czechoslovakia, at that time, was ahead of the USSR in the quality and technical perfection of the motorcycles produced. Java was perhaps the best thing that a Soviet person could acquire for himself back then, and the motorcycle deservedly became a real legend for several generations.

1970 The Java 350 model is entering the market. A powerful, maneuverable motorcycle with a load capacity of 200 kg, a two-stroke engine, disc brakes, and a fashionable and sporty appearance. Java is completely different from other models available on the market. Soviet motorcycles of that time were not far removed in their technical characteristics and appearance from the German models of the 40s, on the basis of which mass production of domestic motorcycles was launched using equipment exported from Germany. Owning a Java motorcycle was considered prestigious, fashionable, and simply a must for anyone who wanted to keep up with the times.

Features of electrical equipment

In many respects, the components and assemblies of the Czech motorcycle were similar to domestic products, but at the same time they differed:

high quality;
amazing wear resistance;
maintainability and long service life.

In those years, Java motorcycles were in short supply, so they were often sold second-hand. And at the same time, the price remained quite high. New owners could immediately get behind the wheel and operate the equipment without any restrictions, because:

wiring to Java did not require maintenance;
the engine had a significant service life;
shock absorbers and suspension had a fairly high safety margin;
consumables were required no more often than provided for by the technical regulations.

Repair instructions for Java motorcycles officially supplied to the USSR

However, the manufacturer constantly modernized its motorcycle models, and each time made changes to components and assemblies. In particular, in different years the following were supplied to the territory of the USSR:

model 559-07 was produced since 1969 under the name “JAWA 250” and was a variant with a 250 cc engine producing 12 hp. with 6V equipment;
model 634 (01-04) was produced from 1973 under the name “JAWA 350” and represented a variant with an increase to 350 cc. cm 16 hp motor, designed to work with 6V equipment;
model 634 (01-08) was produced since 1977 under the name “JAWA 350”, but already with 12-volt equipment and on 16-inch wheels;
Model 638 has been produced since 1986 under the name "JAWA 350". It had only visual differences in the shape of the frame and was equipped with 18-inch wheels (see wiring diagram for Java 638);
Model 640 was the last modification that was officially supplied to our country. It was also designed to operate 12-volt equipment and had differences in design and suspension.

Original wiring diagram for Java 12V model 638

Equipment 6W

For the first 8 years of deliveries from Czechoslovakia, JAWA motorcycles were equipped with equipment designed for a current of 6V.

Original color diagram of electrical equipment Java model 634

There are differences in the above diagram due to modification. In particular, the JAWA 634.8.00 model does not have:

direction indicator warning lamp;
neutral control lamp in the gearbox;
breaker capacitors.

Subsequent motorcycles had these electrical parts installed at the factory. And domestic craftsmen independently equipped their “iron horses” using a new scheme.

Differences in voltage were not an obstacle for owners, who often independently converted the motorcycle’s power supply from 6V to 12V. This required:

replace the generator with a new six-pole one with a self-excitation system of electric current, which made it possible to operate the motorcycle with a completely discharged battery;
replace incandescent lamps with more powerful ones;
install contactless electronic ignition;
replace high voltage wires.

Equipment 12W

Later, the manufacturer recognized the promise of 12-volt equipment and began to equip its products with it. Thereby:

electronic ignition appeared on motorcycles;
changing the generator circuit made it possible to operate the vehicle without a battery (during the daytime);
The luminous flux of the headlights has increased and the brightness of the side lights has increased.

Original photo of the electrical circuit of the model 640 in Czech.
Features of the 12-volt equipment include a bipolar turn relay, which has not previously been found on motorcycles. Its operation scheme is based on the principle of the difference in the current consumption of the control lamp (6W) and the direction indicator lamps (21W):

when turning on the right turn, “+” from the generator or battery enters the right turn circuit, passing through the terminals of the bipolar relay;

in this case, current is supplied to the right front and rear right turn signal lamps;
The indicator lamp is directly connected with one contact to the right turn circuit, and the other to the left turn circuit. When the right turn is turned on, “+” is supplied to the control lamp, and “-” appears in the left circuit of the control lamp for the other contact, coming through the filament of the left lamp of the turn circuit (see also the Java 350 wiring diagram).

What else can be improved?

Some owners improve the exhaust system of the Java motorcycle. Tuning, the photo of which is presented below, is performed by installing direct flows from the mufflers of VAZ cars. The pipe leading to the engine is cut fifty millimeters from the muffler itself, and the outer part is bent at a certain angle. To connect to the elbow, the pipe is cut and installed securely. First, body clamps are welded into the forward flow, and a kickstand is installed on the bike.

The tachometer taken from the VAZ-2106 adds additional aggressiveness and presentability to the two-wheeled unit. It is connected identically to the connection diagram in the car. To install a new starter on a Java, you will need to replace the flywheel, install an additional housing mount and a reinforced battery.

A good innovation would be to change the lighting of the motorcycle. You can choose LEDs to match the color of the unit or play with contrast. The lighting of the rims, exhaust pipe, engine and other main components of the device will look original.

Exhaust system improvement

Another significant thing in tuning the Java 350 is the exhaust system. Unlike a 4-stroke engine, in a 2-stroke engine the cylinder is filled by purging the cylinder. With a properly assembled resonator, a fresh fuel mixture effectively fills the cylinder, and due to the conicity of the resonator, the sound wave is reflected. Thus, part of the mixture does not fly out into the pipe, but returning to the cylinder gives up to 20% more power. You can weld such a resonator with your own hands from sheet steel 0.6-0.8 mm thick, and argon or semi-automatic welding is recommended. The exhaust pipe of the resonator can be made by shortening the standard one by increasing the cone according to the drawing:

According to the figure, the engine will have a sharp pickup and increase in power around 5000 rpm. The damping nozzle is not necessary and only performs a noise-absorbing function. As with tuning the Voskhod motorcycle, this resonator can be used in the same way.

The significant mass of the crankshaft has high inertia, which is done for smooth operation of the engine. By lightening it, you can achieve a sharp response to gas and improved acceleration dynamics. Keep in mind that with this modification of the engine, it is extremely reluctant to operate at idle and low speeds. And of course, don’t forget about replacing the ignition from a contact system to an electronic microprocessor system.

“Boring” a Java engine

Upgrading the Java 350 engine with your own hands is only possible if you know how to work on various machines. To carry out work to increase power, it is necessary to dismantle and completely disassemble the engine. Next, examine the condition of the gearbox and gearbox parts; if they are severely worn, further modifications to the engine will be of no use. After inspection, you should begin polishing the purge, inlet and outlet channels.

After this, it is necessary to remove the jumpers at the bottom of the piston “windows”, and the piston pin skirt can be ground down to a cone. It is also advisable to polish the piston crowns so that less carbon deposits are deposited on it. To increase the compression ratio, it is necessary to trim the heads of all cylinders by 1.5-2 millimeters. After this, the load on the crankshaft will increase during engine operation. If the work is carried out correctly, the power of the Java two-stroke engine can be increased to 23-24 horsepower.

Trimming the cylinder heads of a Java 350 motorcycle

The large mass of the standard crankshaft is necessary for greater load capacity of the bike and maintaining stable idle speed, but this circumstance has a negative effect on the dynamics.

After repressing, there may be dips at idle, but acceleration dynamics will improve. To lighten the crankshaft, it is necessary to use turning, milling and boring machines. It is better to replace the bushings of the lower connecting rods after repressing the crankshaft, especially if they are already quite worn.

Replacing the bushings of the lower connecting rods of the Java 350 motorcycle

The final part of the tuning is to redo the ignition of the Java 350 motorcycle. Experts recommend completely replacing the entire system with a dual-circuit system from a VAZ 2108 with a hall sensor. It is best to replace the factory carburetor with an analogue from the Jawa 638 version, for which it will be necessary to make a special adapter. And remember that you can use the updated power “to its fullest” only after high-quality fine-tuning of the brakes and balancing.

Java tuning and modification of various parts of the motorcycle

Java motorcycle tuning with your own hands. What can be improved in the Java model. Increasing power and other characteristics of the motorcycle.

The efficiency of tuning Java 638 can be significantly increased by dividing the intake channels into two separate ones for each cylinder with its own carburetor.

"Java": do-it-yourself tuning

Using an example, let's look at how to make a forward flow for a motorcycle yourself. It will add originality and also make the engine sound more roaring. To work you will need:

steel sheet 0.8 mm thick;
standard exhaust pipes from modifications with the 638 engine;
metal scissors;
"Bulgarian";
hammer;
welder.

The dimensions of the new element are calculated in such a way that the cone-shaped rear part is located opposite the shock absorber clamps. This advice is relevant if the pendulum has not been replaced and the frame has been lengthened. The forward flow muffler is made of metal sheet in a cone shape. The working parts of the new part go into cylindrical tanks filled with mineral wool.

It is appropriate to improve the power unit of a motorcycle yourself if you have experience working on various machines. Modernization will require dismantling and complete disassembly of the motor. In addition, it is necessary to replace the worn parts of the gearbox and gearbox, otherwise there will be no practical use from the alteration. After this, you can start boring the cylinders, having previously polished the intake, exhaust and purge valves.