DIY 4t scooter engine repair

A list of the most common scooter problems that you can fix yourself without the help of specialists.
Crime: the brake light does not light up, the brake lever limit switch does not work.
Analytics: the lever of one of the brakes has not been pressed or a malfunction has occurred in the brake light circuit.
Procedure: replace the bulb, adjust the brake lever free play or replace the brake lever limit switch.

Crime: fuse blown.
Procedure: check and, if necessary, replace the fuse for the main circuit and the starter circuit.

Crime: the junction of the terminal with the wire is covered with a loose coating of oxides.
Analytics: the battery gives insufficient voltage, which can happen due to a malfunction in the circuit or if the battery terminals are oxidized.
Action: check the circuit, recharge the battery if necessary. Clean the terminals from oxides.
A temporary measure is to start the engine with a kick starter.

Crime: you turned on the ignition, pressed the brake lever and the starter button, and the starter relay still does not click.
Analytics: the electric starter circuit is faulty.
Actions: clean the contacts on the relay and starter, "ring" the relay, wiring, starter windings.

Crime: when you press the kick-starter lever, it scrolls, but the engine crankshaft does not rotate; the leg does not feel resistance to the stroke of the kick-starter lever.
Analytics: Kick starter or ratchet gear teeth are broken. Action: replace defective parts.
Crime: the electric starter turns the crankshaft, but the engine does not start.
Analytics: the carburetor is "dry" (unscrew the drain screw of the float chamber - see). Variants of reasons: the filter of the gas valve is clogged, the gas valve is faulty, the fuel line is clogged, the vacuum hose for the control of the gas valve has jumped off or is leaking.
Actions: clean the fuel tap filter, blow through the fuel line, make sure that the automatic gas tap is in good working order.

Crime: fuel is supplied to the carburetor, but does not enter the pop-up chamber.
Analytics: float fuel valve stuck.
Procedure: remove the float chamber cover and clean the valve seat. If it does not help, replace the valve.

Crime: you unscrew the candle, and it is "wet" - covered with a layer of unburned benzo mixture.
Analytics: excessively rich combustible mixture, which happens due to too high fuel level in the float chamber or due to clogged air filter.
Actions: disassemble the carburetor, check the fuel level, clean the air filter.
Side effects: The engine starts immediately if a little gasoline is poured into the air filter.
Analytics: the automatic starting enrichment does not work.
Actions: check the serviceability of the starting enrichment (there are several ways - they are described in detail in the repair manuals)

Crime: a spark does not occur on a spark plug unscrewed from its socket (in a position where the metal part of the spark plug reliably contacts the "mass" of the scooter).
Analytics: the spark plug is faulty: the insulator is broken or the electrodes are covered with a thick layer of carbon.
Procedure: Clean the spark plug with emery paper or replace. If the spark still does not appear, diagnose other elements of the ignition system.

Crime: the spark on the spark plug is formed, but weak or "running".
Analytics: the spark plug has a broken insulator.
Action: replace the spark plug.

2. THE ENGINE STARTS WITH LABOR, RUNNING UNSTABLE
Crime: the engine does not "spin", there are pops in the carburetor.
Analytics: excessively lean fuel mixture, a possible cause - air is sucked in through a loose intake manifold or damaged crankshaft oil seals. Water in the float chamber.
Procedure: replace the gasket under the branch pipe and evenly tighten the bolts of its fastening. Replace the crankshaft oil seals. Get rid of the water in the float chamber (by unscrewing the drain screw of the float chamber), blow out the jets and channels of the carburetor, replace the gasoline in the tank.

Crime: a spark on an unscrewed spark plug (in a position where its metal part reliably contacts the "mass" of the scooter) is formed, but the surfaces of the insulator and electrodes are dry.
Analytics: the automatic starting enrichment does not work (if the engine is cold). Normal combustible mixture does not form. The idle air jet is clogged.
Actions: check the serviceability of the starting concentrator (see item 1). Purge the carburetor jet and channels.

Crime: there are water droplets on the insulator and electrodes of a twisted spark plug. Analytics: water penetrated into gasoline.
Action: get rid of water in the float chamber.

Crime: a spark on an unscrewed spark plug (in a position where its metal part reliably contacts the "mass" of the scooter) is formed, but the surfaces of the insulator and electrodes are covered with black oily soot (photo 5).
Analytics: the brand of the spark plug does not correspond to the thermal mode of the engine operation - its glow rate is higher than that set for the given engine (the spark plug is "cold"). The temperature in the working area of ​​the plug is insufficient for self-cleaning of the electrodes.
Action: replace the spark plug with a "hotter" one (with a lower glow number).

Crime: the engine starts normally, but soon there are interruptions in its work and it stalls.
Analytics: the vent hole in the fuel tank cap is clogged or the hoses responsible for communicating the contents of the gas tank to the atmosphere are clogged.
Procedure: Clean the fuel tank cap vent or hoses.

Crime: when you press the kickstarter lever, there is no resistance to compression of gases in the cylinder.
Analytics: the piston, cylinder, piston rings are extremely worn out.
Actions: check the compression - using a compression gauge or by measuring the parts (after dismantling the cylinder). Upon confirmation of the diagnosis, the engine requires repair with replacement of worn parts.

Crime: the sound of escaping gases is heard, oily traces are formed on the head and cylinder.
Analytics: the gasket under the cylinder head is damaged or the fastening of the head to the cylinder is loose.
Actions: replace the gasket and tighten the nuts securing the head to the cylinder with the required torque (effort) in the sequence recommended by the repair manual.

3) EXTRAORDINARY SOUNDS IN THE ENGINE
Analytics, version 1: increased wear of parts of the cylinder-piston group.
Action: the engine requires repair with replacement of worn parts.
Version 2: the thermal clearance in the valve drive is broken (for 4-stroke engines).
Action: adjust the valves.
Version 3: Loose chain in the valve drive (4-stroke engines).
Action: adjust the chain tension.
Version 4: grooves in the variator pulley have developed, along which the rollers move, as well as the rollers themselves.
Actions: replace the worn pulley, rollers (possibly other variator parts).

4. ENGINE STOPS AT SHARP OPENING OF THE THROTTLE
Circumstance 1: The engine has just started.
Analytics: the engine is not warm enough.
Action: continue warming up the engine at idle speed.

Circumstance 2: The engine is well warmed up.
Analytics version 1: carburetor not adjusted.
Actions: adjust idling speed, if necessary - the main dosing system (see item 5).
Version 2: the variator does not work properly.
Actions: see item 10.

5.ENGINE STARTS NORMALLY BUT IT DOESN'T SPEND
Crime: thick smoke in the exhaust, excessive fuel consumption, black plaque on the spark plug electrodes.
Analytics: The main dosing system prepares an overly rich mixture.
Actions: adjust the quality of the mixture - lower the carburetor throttle adjusting needle one notch (groove) down. It may be necessary to install a smaller bore main jet.

Crime: the engine overheats, detonation is heard during acceleration, white bloom on the electrodes and spark plug insulator. After turning off the ignition, the engine continues to run for a few seconds (detonates).
Analytics: The carburetor's main metering system is preparing an overly lean mixture.
Actions: adjust the quality of the mixture - raise the carburetor throttle adjusting needle one step up. It may be necessary to install a large bore main fuel jet.

Crime: the engine runs unusually quietly (although it is easy to start), low-smoke exhaust, the engine “does not pull” during acceleration.
Analytics: muffler, channels and cylinder windows clogged with carbon deposits (in two-stroke engines).
Action: clean carbon deposits if possible. If the muffler is completely clogged (no air flow), replace the muffler.

6. AFTER A LONG DRIVE, THE ENGINE LOSES POWER
Circumstance 1: an air-cooled engine.

Crime: no air movement is felt from under the cylinder casing, and a sheet of paper does not "stick" to the air intake mesh (on the right side of the engine) (if a test is carried out with paper).
Analytics: the fan impeller blades are broken, another assumption is that the shrouds of the cooling system are loose or split in places.
Procedure: Replace the impeller and damaged covers.

Circumstance 2: Liquid-cooled engine.
Crime: coolant leaks, its level in the tank has dropped.
Analytics: faulty components of the system: pump, thermostat, radiator.
Action: replace faulty components.

7. ENGINE DOES NOT ACCELERATE THE SCOOTER TO 50 KM / H
Inspection data: speedometer calibrated, no power or rev limiter installed.
Analytics version 1: The scooter is not designed for this speed.
Actions: all actions are meaningless.
Version 2: the carburetor is incorrectly adjusted, the muffler is clogged, or the parts of the cylinder-piston group are worn out.
Actions: see item 2 or change the scooter.
Version 3: the variator is not working properly.
Actions: see p. 9, 10.

8. WHILE THE ENGINE IS RUNNING THE SCOOTER DOES NOT START FROM THE PLACE.
Crime: the variator is faulty.
Analytics: the driven pulley spring is broken, the V-belt is torn (to make sure of this, remove the variator cover - breakdowns are perceived at a visual level).
Action: replace defective parts.

Crime: faulty centrifugal clutch.
Analytics: the springs of the shoes are broken, the linings of the shoes are excessively worn out (found out during a visual inspection after removing the variator cover) (photo 9). Action: replace defective parts.

9. THE SCOOTER RIDES IN SPECTS
Crime: jerks are felt when driving.
Analytics: the variator belt slips (due to wear, damage or oiling) or the surfaces of the pulleys are excessively worn out.
Action: replace defective parts (photo 10).

10. SCOOTER SPEEDS SLOWLY, RIDES SLOWLY
Analytics: during the recent tuning, the weight of the centrifugal regulator weights or the spring of the driven pulley are incorrectly matched. The springs of the centrifugal clutch shoes are broken or have lost their rigidity, the linings of the centrifugal clutch shoes are worn or oiled.
Actions: carry out the tuning more thoroughly, preferably with the participation of specialists.

In order for the engine of a four-stroke scooter to work perfectly, only three things are needed: spark, fuel and compression.When troubleshooting, you should adhere to the following rule - everything is checked gradually, from the most elementary malfunctions to the repair of the main parts of the moped.

The first thing to check is the presence of fuel in the tank and in the system. Then we check for a spark. The engine will not start if the quality of the mixture is disturbed, or if the carburetor is clogged.

If the ignition key is not turned, a fuse is blown, or the battery is discharged, the engine will show no signs of life. Therefore, before proceeding with a global repair, you should check these reasons.

The starter motor cranks, but the engine will not start.

Possible reasons - the spark plug is broken, the carburetor is clogged, the fuel does not enter the system.

The engine runs erratically or a loss of power is felt.

This may indicate that the carburetor is clogged, the oil or air filter is clogged, the head valves are misaligned, the variator or piston group is worn out.

There was a specific knock in the engine during operation.

This could be a sign that the bearings are out of order and need to be replaced. It may also be associated with the need to adjust the valve clearance.

1. We remove the engine from the scooter. We install the scooter as stable as possible. We remove the trunk. Disconnect all wires from the engine and the throttle cable from the carburetor. Remove the gas hose and vacuum filter. Disconnect the rear shock absorber. After the engine has been separated from the frame, unscrew the nut on the mounting axle and remove the axle. After removing the engine, it is advisable to wash it.
2. Removing the cylinder head. It is necessary to do to clean the chamber from carbon deposits. In order to remove the head, you must first disconnect all the "extra" parts. Then the chain tensioner bolt and locking bolts are unscrewed. Then we turn the flywheel until the T designation matches the one on the engine body. We unscrew the bolts on which the cylinder is attached and remove the chain, and then the cylinder head itself.
3. Valve clearances must be adjusted if a metallic knock appears. The principle of operation is as follows: the cover of the valve mechanism is removed. The mark on the flywheel is related to the mark on the engine housing. We measure the clearance between the adjusting screw and the valve stem. When increasing or decreasing the gap, we adjust by rotating the screw.

As practice shows, it is better to entrust the engine overhaul to professionals, since there are many nuances that an ordinary driver does not pay attention to, but which in the future can create even greater problems and then more expensive repairs will be required.
A video on repairing a 4-stroke scooter will introduce you to the main aspects of repair.

In order to disassemble the engine of a Chinese scooter, you don't need to be a super-mechanic or an overly gifted person. First of all, you need desire, accuracy and the availability of the necessary tool. Unfortunately, there is nowhere without a good tool. There are, of course, people who repair scooters with a crowbar and a sledgehammer, but if you do it for yourself and for a long time, then you need to use only good tools. If you do not have the tools, then it is better to leave this venture.

• Alternator puller (you can do it yourself)
• CVT puller (you can do it yourself)
• Kickstarter sprocket remover (157QMJ engine only)
• Heads for 8, 10, 12, 17 mm
• Phillips and flat head screwdriver
• Small hammer
• Wish

Most of China's four-stroke scooter engines can be classified into two main types

1. First type: 139QMB-series engine. This engine is very popular in the CIS countries and is installed on most Chinese four-stroke scooters.
2. Second type: 157QMJ-series engine. This engine has a larger volume than the first and, due to the higher price, is not so popular.

Basically, these two engines are a copy of the ancient Honda GY6 and differ from each other in displacement, kickstarter design, oil pump drive and electric starter drive. Otherwise, these engines are identical.

Typical 139QMB, in fact JL1P139QMB-2

And this is what a typical 157QMJ looks like, in fact LK162QMK

We remove the engine from the frame, drain the oil, clean off the manure of the year before last from all visible surfaces, blow out all the cracks and cavities with a compressor, put it on the cutting table and proceed to an extremely interesting and exciting activity ...

• Remove the muffler
• Remove the cooling shrouds
• Remove generator
• Remove variator
• Clean and blow off connectors
  

It is very easy and simple to remove the muffler: we unscrew two nuts and two bolts on the cylinder head that secure the muffler to the frame (139QMB) or the rear wheel amplifier (157 QMJ)

The cooling shrouds are even easier to remove: we turn off all the bolts and screws that attach the shrouds to the engine and remove.

But the generator is not so simple. The generator can only be removed with a puller. All your attempts to knock down the rotor with a hammer or pick it up with a crowbar are doomed to failure in advance.

We unscrew the bolts on the cooling impeller and remove it and the rotor

We fix the rotor with a puller and unscrew the nut (right thread)

We install the puller and pull the rotor off the crankshaft journal

We blow out the generator, unscrew the bolts and remove it somewhere further

Remove the variator cover. There is nothing difficult in this: we turn off all the visible bolts and remove the cover from the engine. On the 157QMJ engine, so as not to bend the kickstarter return spring bracket, first remove the crank, remove the retaining ring from the kickstarter shaft, and only then remove the cover itself. You can, in principle, and so remove, but then you have to trim the bracket a little.

Removing the variator is not much easier than removing the generator. As with a generator, you need a good puller. Fortunately, the puller can be made by yourself: for the 139QMB engine, instead of the puller, you can use a metal plate: remove the bendix from the niche, insert the plate into it, rest the variator impeller tooth on the plate and unscrew the nut.

You can also make a more advanced puller: we are looking for an unnecessary clutch disc from an IZH motorcycle, we weld a bar and several hooks for the impeller teeth to it

For the 157QMJ engine, the puller is done a little differently.

You can go to the nearest tool store and buy a universal wrench for the grinder. For removing the variator of the 157QMJ engine, it fits very well and costs a penny

The principle of removing the variator is identical to that of removing the generator: fix the impeller with a puller, unscrew the nut, remove the variator from the axle. After removal, we completely disassemble the variator and check all its parts for wear.

On the 157QMJ engine, there is a kickstarter gear behind the variator. It is not so easy to remove, but if you are going to subsequently half the engine, you will have to remove it.

We clean and blow out the cylinder connectors, cylinder head and valve covers. We unscrew the bolts on the valve cover and remove it from the head

We turn off the nuts and bolts on the cylinder head

Remove the camshaft bed. The camshaft bed is virtually wear-free. After removing it, it is enough to wash it and check for cracks.

We remove the chain from the camshaft and take it out of bed. The camshaft has two problematic points that are worth paying attention to: wear of the support bearings and the working surfaces of the cams.

The cylinder, head and camshaft bed are centered relative to each other using guide bushings. These bushings have the ability to fall out of the sockets and then try to find it. To avoid this - immediately remove the bushings and put them somewhere further away. Hereinafter, the bushings will be indicated by arrows.

Remove the cylinder head.The cylinder head is the most vulnerable part of the engine and the operating parameters of the engine directly depend on its condition. In order not to have problems later: the head must be completely disassembled, inspected for cracks, cut the valve seats, put new valves, grind the valves to the seats, put new oil seals and grind the plane on the plate or milled

Remove the cylinder. We check the cylinder immediately after removal for liner wear and the presence of seizures on the mirror

We take out the retaining ring from the piston boss, push the finger out of the upper connecting rod head, remove the piston. We check the piston for cracks and wear, pay special attention to the condition of the grooves for the rings and the rings themselves

We unscrew the bolts on the cover (there are fewer bolts by 139QMB: 8), slightly hammer it with a mallet and remove it from the engine. The crankcase guides will be marked with arrows as in the case of the cylinder head. The covers, especially on 139QMB engines, break even if the scooter falls slightly. When you remove the cover - carefully inspect its body and if the cracks are not significant - weld them at the nearest "argon"

157 QMJ looks more complicated inside

To disassemble 157QMJ you need to do the following:

• Remove the starter intermediate gear
• Unscrew the nut on the freewheel
• Remove the chain from the oil pump
• Unscrew the last bolt tightening the engine crankcase

With 139QMB, much less fuss:

• Remove the oil pump gear
• Unscrew the last bolt tightening the crankcase

We take an old blunt screwdriver and use a hammer to unscrew the freewheel nut (left-hand thread: unscrew strictly clockwise!)

Press on the drive chain:

• A good chain should have some slack. Such a chain can still be operated
• If the chain is worn out, the slack will be maximum. Such a chain should be thrown out.

The chain is in average condition. The new chain practically does not sag when pressed on it

Remove the protective screen of the oil pump

We put a tin bar or stick under the chain, unscrew the nut on the oil pump sprocket, remove the sprocket from the shaft, remove the chain

On 139QMB we do almost the same thing: hold the sprocket with our hand, unscrew the nut, remove the gear from the shaft. On some 139QMB models, the gear can be without a nut, if you have done so, then you are in luck: take out the gear and housings and that's it.

We unscrew the last bolt tightening the crankcase and use a wooden mallet to half the engine

We take out the crankshaft from the crankcase and check it for suitability for further operation

We check the timing chain for wear, but it will be better if you throw it away immediately. At this, the epic with the disassembly of the engine can be considered over. As you can see, there is nothing difficult in this. But it is up to you to disassemble the engine yourself or send it to the workshop.

On scooters, a fairly common problem can be the occurrence of foreign noise. In this case, you can repair the scooter engine with your own hands. To do this, you need to understand how you can determine the cause of their occurrence and how you can deal with it.

Basically, the occurrence of foreign engine noise on a scooter can occur due to the wear of various parts. The motor in a scooter is subject to gradual wear, however, like almost all other mechanisms. Some parts are subjected to colossal loads during operation, which is why over time they can simply become unusable. It is necessary to understand in time that there are some problems with the engine, because due to the wear of one element, the performance indicators of others can significantly decrease.

Scooter engines have a much lower service life in contrast to automotive units. For this reason, the scooter owner must make timely diagnostics of the engine operation.And if suddenly some malfunctions appear, then do-it-yourself scooter engine repair is required.

When some parts of the engine wear out, a variety of sounds can occur during its operation, for example, chirping or light ringing. They can appear at high speeds, as well as at idle. In addition to noise, the scooter may lose the previous level of dynamics, experience some problems while driving, and also not reach high speed. If such problems appear, then you need to think about repairs. If the breakdowns are insignificant, then you can do it yourself with certain knowledge and tools.

If the power unit functions normally at idle, but howling occurs when a high speed is set, then the crankshaft bearing may well fail. Such parts cost relatively little, which is why it is not recommended to neglect their timely replacement. Better not to save in this case. If the scooter engine will be repaired independently, then you need to be as careful and calm as possible. During assembly and disassembly of the engine, the basic repair rules must be observed, that is, there is no need to rush. When new bearings are installed, it is also very important to keep clean, because just one grain of sand in the motor can have a serious negative impact. It will also not be superfluous to flush the old bearing in gasoline. This is necessary to remove the grease. If you cannot dismantle it yourself, then it is recommended not to risk it, since careless actions can cause damage to the crankshaft. But if everything went well, then the bearings need to be run in.

Another popular problem with an engine is piston wear. Rings can wear out rather quickly. If there are problems with starting the engine and at the same time a metallic ringing is heard, then the piston grooves are probably worn out. In this case, the piston must be replaced. It is important to do this in a timely manner.

In order for an internal combustion engine to work, it needs three components: fuel, spark, compression. The main slogan of the motor mechanic is “miracles do not happen”. It must always be remembered that if, when troubleshooting and scooter repair it turns out that there is a spark, there is compression, fuel comes in, but the engine does not start, this usually means only that some of these components are actually missing.

Too lazy to give the scooter for repair and pay money for it. Familiar situation. Then it's time to take on the repair with your own hands.

The basic principle of troubleshooting and repairing a scooter is to exclude system elements step by step, trying to identify the cause of a malfunction in one of them. Search and repair must be carried out strictly sequentially, from the very beginning of the chain to the very end. That is, for example, in the absence of a spark, you should not immediately change the switch. First, you need to make sure that we have a "live" generator, then test the wiring. Etc.

An important note: if you have a device in front of you, which, according to the owner, “used to work like a clock”, it makes sense to ask if old gasoline is poured into the tank. A couple or three months of storage is quite enough for gasoline to lose its octane number to such an extent that it has lost the ability to ignite.

It is important to remember that before making the final diagnosis and starting the repair of the scooter, you need to make sure that a working candle is installed on it, as well as the carburetor is functioning normally.

In addition, you need to know that the correct operation of the engine (even at idle) is closely tied to the correct operation of the variator, clutch, as well as the camshaft and valve group.In other words, with normally functioning power supply, ignition and CPG systems, the problem may be, for example, in the transmission, since the crankshaft torque is directly transmitted to the variator.

When carrying out diagnostics and repairs, it must be remembered that under some circumstances that led to the need scooter repair, it is necessary to check not a single element, but the entire system. For example, if the carburetor is clogged, provided that the air filter is intact and impregnated, it is necessary to check if there is any dirt in the gas tank and fuel filter. If the scooter has been driving for a long time without an air filter, or with an untreated filter, then everything must be checked: the CPG, the crankshaft and the main bearings.

Below are some of the problems that you may encounter and the basic steps to take to fix them. The links indicate the places where you can find information on this item.

In our country, scooters are a fairly popular two-wheeled technique that occupies the minds of young people, as well as older men and women. It is not surprising, because there is no more such a miniature, economical and convenient in many ways transport, at a reasonable price. However, despite its modest dimensions and tiny engine, the scooter can also be quite fast. In this article, we'll talk about tuning a scooter, what is it like and how much does it cost?

Tuning scooters is a fairly extensive process, but consists mainly of styling (improving the appearance), tuning the chassis (modifying the ride performance) and tuning the engine. The last point consists of many different operations, which are aimed at increasing engine power, better implementation and increasing acceleration and maximum speed. Below we will consider precisely the modifications of the engine and transmission.

It should be noted right away that the scheme is general and is suitable for Italian, Japanese and Chinese models. Those who doubt the quality of Chinese scooters should be reminded that the level of production of modern models from the Middle Kingdom has grown significantly over the past 10 years, and most of the spare parts on the market for all models are from Chinese manufacturers.

There are many ways to speed up your scooter, and first of all they depend on the current technical condition of the unit. Take, for example, an old scooter with an incorrectly tuned variator, clogged air filter, dirty carburetor, and a number of other problems that arise from improper maintenance of equipment. The potential of such an engine is great, but it can be realized only after correct tuning. Once all systems have been thoroughly cleaned and tweaked, even standard motor performance seems like a significant improvement.

It follows from this that any work aimed at improving driving performance should begin with a complete revision of the engine.

Removing the factory restraints is a very popular type of tuning and is quite simple. Most of the Japanese equipment and similar Chinese ones come from the factory with special limiters that prevent the engine from working at full capacity. Fortunately, you can get rid of the restrictions in any garage and any tuning of a scooter with your own hands begins with the elimination of such restrictions.

When childhood diseases are over, you should pay attention to real tuning, namely, improvement or modification of existing components and assemblies. We are talking, of course, about the cylinder-piston group, carburetor, muffler, variator, air filter and ignition system. At this stage, the degree of involvement in improving a particular element depends on the budget. If funds are limited, then we will maximize the squeeze out of the existing set, by modifying the described nodes.

If there is a certain budget for tuning, you can follow the path of replacing parts with special tuning ones.Special parts designed for such modifications automatically improve the main characteristics of the engine, plus they are designed for higher loads. We figured out the general scheme of improvements, and below we will consider how tuning takes place, using examples of specific nodes.

Experts, connoisseurs or garage masters start tuning a scooter with their own hands by dismantling the factory restraints. They are necessary in order, firstly, to keep the equipment within the established speed limits (Japanese models), as well as to increase the resource of the motor. The problem is that you can find this item only after studying your engine model in various forums. The reason for this is the different locations of these same limiters, so it can be a blind fork in the exhaust, an electronic limiter installed on the variator or even in the carburetor.

• A plug in the variator. In this case, the part is a special plate mounted on the side of the weights. It prevents the belt from reaching the maximum radius, which means that it is impossible to reach the maximum possible speed. If you have such a part, then removing it you can significantly increase the maximum speed.
• Limiter in the variator. Sometimes the side on the bushing itself acts as a limiter; here you cannot do without the work of a turner. The speed can be increased by squandering the clutch flange of the variator. Also, for many models, a ready-made, bored part is sold.
• Carburetor. In this assembly, the plug looks like a valve. With a significant increase in pressure, it opens, thereby preventing the full flow of the fuel-air mixture into the combustion chamber. All this is treated, as in the previous versions - by dismantling the element or replacing the whole part.
• Exhaust. An interesting restrictive system is located in the exhaust. It is a fork, where one of the channels is a dead end. Thus, the turbulence and internal pressure in the exhaust are increased, which prevents good purging of the combustion chamber. The problem can be solved by welding dead-end forks.
• Electronic system. Finally, the switch limiter can be considered the most advanced by modern standards. Some Chinese and Italian models can be fooled, we will have a bite of the limiter wire, for this we will have to study a lot of literature on electrics. The rest of the models get rid of the problem by simply replacing the assembly.

As mentioned earlier, the engine must be serviced before forcing. Work that will help improve dynamics include valve adjustments. The procedure is suitable for tuning Chinese 4t scooter and other 4-stroke motors. For small-sized equipment, it is recommended to carry out such an adjustment at least once every 3, and preferably every 2 thousand km. It is also necessary to carry out the adjustment after manipulations with the CPG.

Before starting work, you need to make sure that the engine is completely cool and that you have a set of keys (8.9) and 0.05 mm probes for the inlet and 0.07 mm for the exhaust valve at hand. You can get to the adjusting nuts by first removing the valve cover. When access to the valves opens, the piston is set at top dead center. Next, a dipstick is installed in the intake valve clearance and, depending on the current position, an adjustment is made.

To increase or decrease the clearance, loosen the lock nut (while holding the adjusting bolt), turn the adjusting bolt, and while holding it, pull the lock nut back. Thus, we achieve a gap when the probe passes into it with little effort. After tuning, rotate the crankshaft a full turn and check that the alignment is correct.

The main principle of fast driving is to burn more gasoline per unit of time, it is suitable for tuning Chinese 4t scooters, Japanese 2t scooters and any other models and types of motors, and the carburetor helps in this, first of all.It is possible to modify the standard unit by installing more efficient jets, but in practice it is better to install more productive models. Tuning of scooters is facilitated by productive models of DellOrto carburetors, a set of pipes and other accessories for them.

A high-performance carburetor will deliver more fuel to the cylinder, and more fuel will need more air. Therefore, the standard filter should be revised, it is best to replace the filter element with a new one, while making sure that the entire system is tight. If a high-power device is being prepared, it makes sense to install a filter of minimum resistance, but do not forget that it needs constant maintenance, otherwise the filter element will dry out and sand will start to get into the engine.