Friday 18 November 2022

Fix kickstart play Ural and Dnepr

 At F2 Motorcycles we sometimes work on older Urals and Dneprs. We are often asked to fix them on a limited budget. These bikes may have not functioned well for some time and one of the things that fails is the kickstart shaft where the kick start attaches using a wedge bolt. They may have been kicked and kicked in desperation as the owner tries to start a bike with underlying running issues. 

The flat part of the kickstart shaft and the wedge bolt both start to wear and the kickstart starts to slip. Once this happens the kickstart shaft wears very quickly and it's not too long before most of the kickstart movement is simply damaging the shaft rather than turning the engine over. 

For comparison this is what one looks like with no wear. 

Obviously the correct fix is to take the gearbox apart and replace the kickstart shaft then refit the kick start with a nice new wedge bolt. There is a low budget fix which we have used many times and if done correctly lasts for many years. You will need some metal loaded epoxy glue such as JB Weld and an old feeler gauge. These feelers are made from a very hard metal that does not crush easily. Cutting them is fairly difficult, but we find a Dremel with a cutting disc works well. You only need a piece large enough to cover the damaged area of the kick start shaft. 0.3mm to 0.5mm thick seems about the correct thickness but this will depend on the amount of damage to the kick start shaft. 

Degrease the kickstart shaft and then glue the piece of feeler onto the damaged surface using a high quality metal load epoxy such as JB Weld. 

Allow the epoxy to fully cure and then carefully file the excess away so the kickstart lever and wedge bolt can be refitted to the kickstart shaft. 

Refit the kickstart lever using a new wedge bolt. There should be zero play, If there is any at all it will wear quickly, We have carried out t repair many times with good results allowing many more years of use without going to the expense of a new kickstart shaft and the labour cost of fitting it. 

We have carried out this repair many times in order to keep our customers on the road while keeping the repair cost low. Many are still functioning perfectly years later. 

Saturday 23 May 2020

Ural and Dnepr Clutch Push Rod Repair.

Both Ural and Dnepr use a clutch push rod operated by a lever on the back of the gearbox. The rod runs though the input shaft of the gear box and includes a thrust bearing sandwiched between the clutch release slider and the release rod tip. There is a small hollow in the clutch release slider to hold grease and the thrust bearing should be greased when it is fitted.

The design is OK rather than excellent. The bearing consists of 6 ball bearings housed in a brass (or plastic) holder. Being spherical only a tiny area of the ball bearing is in contact with the surface of the clutch release slider and release rod tip. This causes very rapid wear. The balls wear a track in both the release slider and rod tip. Once the track is deep enough, the brass (or plastic) bearing holder makes contact with the release slider and rod tip. At this point the thrust bearing can no longer do the job it needs to, leading to rapid wear of the clutch release rod and the clutch pressure plate. The picture below show the tracks worn in the release slider and rod tip.

The standard "fix" for this is to replace the thrust bearing along with the clutch release slider and the release rod tip. The wear process can then start again. This situation is made worse by the fact that nearly all the spares available today are nasty cheap pattern parts. These are not surface hardened at all and will usually last less than 500 miles. The picture used above shows the wear on parts supplied from eBay after a little under 200 km. Genuine parts are harder wearing but nearly impossible to obtain. Dnepr closed in 1998 and Ural changed their design in 2007 so no longer supply original parts.  

F2 Motorcycles Ltd have a solution that not only fixes the issue of the worn bearing tracks but offers a far superior bearing with a much longer life. The original clutch release slider and release rod tip are retained. A perfectly flat surface ground and hardened disc sits over the damaged part covering the worn track and giving the new caged needle thrust bearing the perfect surface to run on. The ball type bearing that caused all the trouble in the first place is discarded and a caged needle thrust bearing is used in its place. The two discs plus the replacement bearing combined are almost exactly the same width as the original ball bearings so everything fits and works perfectly. If the bearing is well greased before fitting and again every 10000 km this upgrade will last the life of the bike. 

Monday 6 January 2020

Lithium Motorcycle Batteries

LifePo4 batteries.
Not that long ago if your motorcycle needed a new battery you simply had to decide between various types of lead acid batteries. They all use the same chemistry and only differed in terms of how that chemistry is packaged and the quality of build.

Wet fill lead acids batteries are always the lowest cost, and to be honest in a kick start bike with no high current loads they last OK. They often die simply due to lack of maintenance as the acid level slowly drops over time and needs topping up with distilled water.

Absorbent Glass Matt or AGM offer more convenience and are often sold as zero maintenance. They are filled with a pre-measured amount of battery acid either by the shop or the owner just before fitting, the top is then sealed and that’s that, no further maintenance can be done. The chemistry is just the same as wet fill, but the acid is held in a fibre glass matt and this matt can be very thin so AGM batteries can be built with the plates closer together and in some cases with more plates per cell, this in turn allows them to supply higher current which is useful for electric start bike.

Top end specialist sealed batteries, these were always factory filled and supplied pretty much ready to fit. They are variations on the AGM battery, but built to a very high quality, some even have spiral plates to increase the surface area. These are always the most expensive lead acid type, but often offer much higher maximum current known as Cold Cranking Amps (CCA) which can be very useful for higher compression electric start bikes or those used in the winter.

But now there is a range of lithium batteries designed to directly replace the lead acid battery in your motorcycle.
It’s important to understand the terminology as “Lithium Technology” seems to cover a range of different types of battery. All are often referred to as Li-ion or Lithium Ion.

Lithium-Cobalt Oxide or LiCoO2 are the smallish batteries used in mobile phones, they charge slowly, they hold a decent amount of energy for their size and they can be discharged slowly. No use at all for a motorcycle. If LiCoO2 batteries are charged or discharged quickly they can go into thermal runaway and catch fire. There have been famous cases of reputable mobile phone makers demanding too much from these batteries, which lead to some much publicise fires.

Lithium Iron Phosphate or LiFePo4 is the only chemistry currently available (2020) to be trusted in a motorcycle. They store much less energy size for size than either LiCoO2 or lead acid. This sounds like bad news, but it can deliver all of that energy very quickly so it is perfect for electric start bikes. There is no real need to store a lot of energy, as soon as the bike starts the alternator will supply all the energy required. To start a bike the single most important thing is cold cranking amps (CCA).

LiFePo4 safety and maintenance is only a concern if it is not understood. Just like a lead acid battery the LiFePo4 battery is made up of several cells inside a convenient box with a terminal at each end. It is vital that these cells are kept roughly in balance so one does not become deeply discharged while the others are charged. If this happens the battery life will be shortened and there is a very small possibility that during charging, the charger (or regulator on the motorcycle) will not cut out as this one low cell is bringing the total battery voltage down, if this situation continued eventually a fire may start due to overheating. So ONLY consider batteries manufactured with an inbuilt factory fitted Battery Management System know as BMS (sometimes referred to as BMC). This is an internal electrical circuit that monitors the voltage of each cell with in the battery and balances the voltage.

LiFePo4 batteries really do not not like being charged above 15 volts, their life will be dramatically shortened, and given the high cost of LiFePo4 batteries this issue should not be ignored. Before fitting a LiFePo4 battery to any bike it is worth taking a voltage reading across the battery with the engine running at various speeds and with various electrical loads such as light on or off. If the voltage regulator on the bike is doing it’s job it will never peak above 15 volts, or if it does it will be for less than one second as it adjusts to different electrical loads. If using a battery charger it is much better to use a charger designed specifically for LiFePo4 batteries, these will never go above 15 volts but equally they will not supply a very low amp trickle maintenance charge which also shortens the life of LiFePo4 batteries. At a push it is possible to use a standard charger of the correct size, whilst monitoring the voltage with a volt meter. Allow the charger to take the battery to about 14 volts and then turn it off. Earlier I mentioned that LiFePo4 batteries store less energy than AGM batteries, and when it comes to fast charging this is a huge advantage. To charge a discharged bike sized LiFePo4 battery may only take an hour compared to 4 or more hours for a AGM battery.

Lets start comparing AGM with LiFePo4 to understand the difference. All these batteries are exactly the same physical dimension and both fit a Jawa 350 OHC.

Battery type
Full Charge Voltage
Energy stored in AH
Cold Cranking
Lead Acid wet fill
Standard mid range AGM
High end AGM

The table shows some interesting things when it comes to starting an engine. The more amps that are supplied the more torque the starter motor will produce, but also worth noting is the more volts that are supplied the faster the motor will spin.

The total energy stored does need to be considered. If the bike is fitted with any alarm or tracker device with a high drain you will need a lot of storage
however good quality modern alarms should have almost zero drain. Still worth checking if you have an alarm and you are considering a change to a LiFePo4 battery. The alarm manufacturer should be able to tell you the drain on standby, anything below 5 mA should be OK.

If you have read any of our other blogs you will know that at F2 Motorcycles Ltd we like to test stuff before deciding if it’s all hype or a useful product.

As the UK Jawa importer we have two nearly identical bikes available to allow comparative testing. Both are Jawa 350 OHC which are 4 stroke singles with Euro 4 fuel injection and electric start. They use a 9 amp battery mounted behind the side panel and like most modern bikes there is no room for a larger battery. Both bikes have covered less than 2000 miles from new, and both are freshly serviced using the same oils. They are both stored next to each other in an unheated area so the temperature should be the same.

One bike is fitted with mid range new AGM lead acid battery the other fitted with new LiFePo4 battery of same dimensions and sold as direct replacement. After fitting, both batteries were given similar treatment, used to start the bike, allowed to charge, allowed to discharge a little by leaving the lights on, charged, bike started and run for 10 minutes, etc. This treatment continued for a few days and both batteries were always treated in the same way. This was only done as in the past we have experienced brand new AGM batteries not performing well until they have been worked a little. The AGM battery was always charged with a smart charger designed for AGM batteries and the LiFePo4 used a similar size charger but one designed for LiFePo4 batteries.

The batteries were than fully charged using the correct charger and left plugged in until the charger displayed the full charge light. They were then unplugged and left for one hour and the full charge voltage reading taken.

A thermometer that records maximum and minimum temperatures was used to give a range of temperatures during the time between each voltage reading.

The batteries were then monitored over time attached to the bike just as they might be if you left your bike in a cold garage in the winter with no charger.

Voltage after full charge 8.2 °C
Voltage after 24 hours at between 5 and 10 °C
Voltage after 3 days at between 5 and 10 °C
Voltage after 7 days at between 5 and 10 °C
Voltage after 14 days at between 3 and 10 °C
Voltage after 20 days at between 2 and 8 °C
Voltage after 26 days at between 2 and 8 °C
Voltage after 30 days at between 3 and 8 °C

After 30 days an attempt was made to start both bikes.
The temperature was 3.2 °C

AGM results are as you would expect for a battery showing 11.5 volts and a temperature of about 3 °C. The engine turned over very slowly once but the engine did not start. On the second attempt the engine didn’t turn over compression. The battery was rested for 15 minutes to recover and a third attempt made, but again although it managed to take the engine over compression once, it did not start.

LeFePo4 results are much more encouraging. On the first attempt the engine turned over reasonably quickly but failed to start, Waited 10 seconds, and the second attempt turned the engine over even quicker but still failed to start. Waited another 10 seconds and the third attempt spun the engine over very quickly, it started and ran.

Different techniques for different battery technology. Lead acid batteries tend to recover a tiny amount if they are allowed to rest for 15 minutes. LiFePo4 batteries work much better if they are slightly warm and the act of pressing the starter button warms them so by the third attempt with just 10 second rests the battery was performing well. There is advice on line suggesting that on very cold days it is worth turning the lights on or holding the brake on to light up the brake lights for a minute before trying to start the bike.

The first test would seem to show the LiFePo4 as the easy winner, but the AGM battery performance seemed almost too bad to be believed.

The first test seemed too bad to be trusted, experiences says AGM batteries don’t like standing about in the cold, but the results seem terrible. Test repeated using another new battery, but a different make from a different supplier at a higher price. Again it was fitted and used for a few days to cycle it a little before the test started. This time the AGM battery was charged using an intelligent charger with winter mode which holds the peak voltage slightly higher during the float stage of charging. This is cheating slightly as many people will have a smart charger, but not so many will have one with winter mode. However if this proves the AGM battery can be used as a reliable starter in winter, it might be worth knowing. There is no winter mode for LiFePo4 so this was charged using the same charger as the first test.

Lead Acid
Voltage after full charge 9.5 °C
Voltage after 24 hours at between 5 and 10 °C
Voltage after 3 days at between 5 and 10 °C
Voltage after 11 days at between 5 and 12 °C
Voltage after 13 days at between 3 and 12 °C

After just 13 days an attempt was made to start both bikes.
The temperature was 6 °C

Surprisingly AGM even at 12.80 failed to start, First turn seemed hopeful but engine failed to catch, second press engine noticeably slower to turn, Voltage after 15 minutes to recover was 12.50. Further attempts to start fail to produce a running engine and the starter simply got slower with each press. At this point we were getting suspicious that there might be something wrong with the bike rather than the battery, so a second battery was linked in parallel to the bike and it started immediately proving the only thing stopping this bike from starting is the inability of the battery to supply enough power to the starter motor. BUT this second battery is far too big to fit to the bike permanently as it is from a small car.

LiFePo4 battery turned engine over at reasonable speed but did not start on first attempt, waited 15 seconds with the ignition on and brake lever pulled in to activate the brake light. 2nd attempt engine turned quickly and started with no problem.

The problem seems to be modern high compression engines need lots of amps to spin them over, modern electronics need a voltage close to 12 to trigger the injectors and ignition system. Small AGM batteries don’t seem to be able to crank the engine fast while supplying good voltage when they are cold. A much bigger AGM battery would work, but there is no space on a modern bike. The LiFePo4 battery does seem to offer something better than the AGM technology but at a price. There is no getting away from the fact they are much more expensive and in order to last well would need a charger designed for them. The final unknown is battery life. There are reports online of LiFePo4 batteries lasting only a few months, but looking in to these they all seem to be cheap batteries with no BMS fitting or batteries that have been left deeply discharged for a while. Generally a good quality LiFePo4 battery fitted with a well made BMS and kept charged regularly by either riding the bike every couple of weeks or by attaching a LiFePo4 specific charger will out last a mid range AGM but may not last as long as the very best of the best AGM costing as much or more than a LiFePo4.

Based on these results we are now offering LiFePo4 batteries and chargers for the Jawa 350 OHC.

And finally just a recap on the safety and suitability of Lithium Batteries. They may all be marketed as Lithium, Li-ion, Lithium-Ion etc, but the ONLY safe reliable ones are LiFePo4 with high quality BMS designed specifically for vehicle use. If it’s on a dodgy online site and looks to cheap to be true it probably is not a reliable and safe LiFePo4.

Monday 12 August 2019

Right Hand Sidecars in the UK

Registration and riding of Motorcycles fitted with the sidecar to the right of the motorcycle.

We often get asked if it is OK to ride a motorcycle with the sidecar fitted to the right of the motorcycle.
Often it is because the customer has seen one on eBay that says it is fine.
These adverts are misleading to put it mildly.

Q. So can you ride a motorcycle on UK roads if the sidecar is fitted to the right of the motorcycle?
A. Yes, but only under the following conditions:

The motorcycles is registered in the UK before 01/08/1981
The motorcycle is permanently registered to you in another country and you are visiting the UK on holiday.

The confusion these sellers rely on when they say their bikes can be legally registered is complex.
1. Any bike of any age can be registered in the UK.
2. The V55/5 used to register a previously used vehicle in the UK does not actually ask if there is a sidecar or which side it is fitted to.
1 + 2 means they are correct in stating their bike can be registered.

However it is important to note there is a big difference between the ability to register a vehicle, and legally using it on the public road. To use it legally it must conform to The Road Vehicles (Construction and Use) Regulations 1986 or newer version where applicable.

Regulation 93 of The Road Vehicles (Construction and Use) Regulations 1986 states the following:

“No person shall use or cause or permit to be used on a road any two-wheeled motor cycle registered on or after 1st August 1981, not being a motorcycle brought temporarily into Great Britain by a person resident abroad, if there is a sidecar attached to the right (or off) side of the motorcycle.”

Lets pick this apart and deal with all the arguments I have heard from people claiming it is legal to ride a motorcycle registered on or after 01/08/1981 with the sidecar on the right.

Argument 1.
My bike was built in 1969, and I registered it in the UK in 2018 so it's fine.
Counter argument:
The act is very specific in the use of the word registered. The bike was registered in 2018 so its use must comply with the Act. The fact that it was built in 1969 is irrelevant.
Argument 2.
But it was registered before 1981 abroad, so it is registered before 01/08/1981.
Counter argument:
This is a UK Act and is concerned with UK registration only. The UK government do not pass acts pertaining to road traffic laws in other countries.
For clarity, simply look at the table of contents at the beginning of the Act. Under the word registered it states:

“registered under any of the following enactments—
(a) the Roads Act 1920,
(b) the Vehicles (Excise) Act 1949,
(c) the Vehicles (Excise) Act 1962, or
(d) the 1971 Act
and, in relation to the date on which a vehicle was registered, the date on which it was first registered under any of those enactments.”

All of these are UK Acts, all apply to the UK. Registered therefore means registered in the UK.

Argument 3.
If DVLA allow me to register it I must be allowed to ride it on the road.
Counter argument:
When you register a used motorcycle in the UK you have to fill out form V55/5. Nowhere on this form does it ask to which side the sidecar is fitted. DVLA will assume that once registered, the rider will adhere to The Road Vehicles (Construction and Use) Regulations 1986 when using it. DVLA are the registration authority, their remit does not extend to how the vehicle is used. This argument is as stupid as saying DVLA allowed me to register a car that can do 120 mph and therefore I can drive it at 120 mph on the road.

Argument 4.
LHD cars are legal so LHD motorcycle and sidecars must be.
Counter argument:
Cars and motorcycles are not the same vehicle and the rules regarding the use of them differ in a number of ways. I'm not saying that it's fair, but that's just how it is.

Argument 5.
But people visit the UK all the time and their sidecars are fitted to the right of the motorcycle.
Counter argument:
Yes they do and the Act allows for this in the statement: “not being a motorcycle brought temporarily into Great Britain by a person resident abroad.”

Argument 6.
My bike has just passed an MOT with the sidecar on the right so I am good to go.
Counter argument:
MOTs are primarily concerned with the condition and maintenance of your vehicle. The MOT test does not specify to which side the sidecar is fitted, only if it is secure, has good tyre tread and decent wheel bearing/brakes and sufficient lighting. So you are not good to go.

Argument 7.
My mate's been riding his for years and never had a problem.
Counter argument:
Well, if your mate had been shoplifting for years, would that make shop-lifting legal?

Argument 8.
I even asked a police officer and he said there was nothing wrong with my bike.
Counter argument:
OK, we all like to think that every police office knows every single law word for word, but this is not the case. This lack of knowledge is exactly why argument 7 is often used.

In conclusion, it seems very clear that using a motorcycle on the road that was first registered on or after 01/08/1981 with a sidecar fitted to the right side of the motorcycle contravenes Regulation 93 of The Road Vehicles (Construction and Use) Regulations 1986. No ifs, no buts, no maybes.
On a serious note, lets say you are involved in a road traffic accident causing serious injury or death to a third party, how will you defend yourself against this statement:
93. No person shall use or cause or permit to be used on a road any two-wheeled motorcycle registered on or after 1st August 1981, not being a motorcycle brought temporarily into Great Britain by a person resident abroad, if there is a sidecar attached to the right (or off) side of the motorcycle.

And finally:
The guys selling online with the statement that the bike can be legally registered are either deliberately misleading you or more probably have not understood the difference between the rules required to register a vehicle and the rules regarding the use of that vehicle on the road.
If they are telling you in writing that it is legal to ride the bike on the road after registration I would say that they are on dodgy ground legally.
93. No person shall use or cause or permit to be used on a road any two-wheeled motorcycle registered on or after 1st August 1981, not being a motorcycle brought temporarily into Great Britain by a person resident abroad, if there is a sidecar attached to the right (or off) side of the motorcycle.

As a legitimate business in the UK dealing with sidecars I will never do anything that may lead any person to believe that they can ignore UK road laws.

Rule 93 is very clear and covers motorcycles registered in the UK regardless of the origin of the vehicle.

So to be clear, if the bike you are considering buying looks like the one in the picture with the sidecar fitted to the right side of the bike when facing the direction of travel. 
If it is not already registered in the UK on UK plates and you intend to register it now. Riding it on the road after it is registered with the sidecar on the right will contravene The Road Vehicles (Construction and Use) Regulations 1986. 
If it is already road registered in the UK simply look at the V5C. The only section you need to worry about is the date of registration. If this date is on or after 01/08/1981 riding it on the road will contravene The Road Vehicles (Construction and Use) Regulations 1986. 

Monday 3 December 2018

Restoring Plastic Headlights

Plastic headlights on modern cars tend to fade to yellow and become very milky over time. Milky yellow lights are much dimmer than clear new lights, but because this happens over a long time most owners don't notice the lights getting worse.

Picture of light before restoration

You need to be brave to tackle this as the lights are going to look a whole lot worse before they look better. If you are brave it's fairly easy to make a huge improvement to the lights in less than 2 hours even without power tools. There are some disadvantages, and I'll mention this later.

The aim is to completely remove the original degraded factory coating, there is just one way to do this and it seems extreme. Sand it off.

Mask round the light so you don't damage the paint, I used insulating tape. BUT wax polish the paint first so the tape does not lift the lacquer when it's removed (yes I learnt this the hard way).

Use 600 grade wet and dry and use it wet with slightly soapy water, no power tools, just round and round, back and forth until the whole light is evenly matt.

Move on to 1500 grade wet and dry, and again use it wet until the whole light is smooth but still matt

Picture of light after sanding with 600

The next bit is easier with a 50mm finishing sponge and a low speed drill, but I have done them by hand, it just takes longer. Use G3 finishing compound (from a car paint shop) and polish the light until is is clear and all the matt finish from the 1500 appears to be gone. It will now look pretty good but just a tiny bit dull or matt.

Use T-cut or similar super fine cutting compound in the same way as you did the G3, and then finally use a high quality war polish to protect the surface.

The lights will look pretty much like new, and the first time you drive in the dark you will amazed at how much better they are.

Light after polishing

Now the disadvantage. The original coating was put on the light by the factory to stop the plastic getting dirty as the surface of the plastic is slightly porous. The coating has gone, you have no protection, so you will have to clean the lights far more often. A good wax polish seems to offer good protection for many weeks.

Friday 31 March 2017

When is an EGR valve Not an EGR valve

When is an EGR valve not an EGR valve.

Just so you know EGR valves send some of the exhaust gas to the air box hence their name “Exhaust Gas Recirculation”. They are generally fitted to large diesel cars.

If you look at nearly any carburettor equipped 125cc engined motorcycles made between about 2000 and 2016 you will see some pipe work routed to the exhaust port or even into the exhaust directly, but very close to the exhaust valve. On just about every forum and facebook page concerned with these bikes you will find all sorts of complete nonsense about blocking the so called EGR valve and how it makes the bike go better, run sweeter and start better. There are even dealers selling EGR blanking kits for these 125s on eBay and similar sites. Read on, I have news for you.

They are NOT EGR valves, they have nothing whatsoever to do with recirculating exhaust gas, they do not dilute your inlet air by sending exhaust gas to the air box, they do not change the performance of your bike, blocking them will in nearly all cases not produce any increase in performance, and it may well damage the expensive catalytic converter in your exhaust.

So what are these valve things on 125cc motorcycles ?
They are Secondary Air Injection (SAI) valves also known as Supplementary Air Systems (SAS).
More accurately as there is no pump in the system they are Aspirated Air Injection (AAI) valves.

So what are they ?
They are a simple diaphragm operated one way valve.
At idle (or tickover) with the throttle shut there is considerable inlet manifold pressure and the valve is open in one direction only. Fresh, oxygen rich air can flow from the air box to the exhaust, but never from the exhaust to the air box.
When there is little or no vacuum created in the inlet manifold for example when running flat out on a flat road with a wide open throttle the valve is closed, now air can pass through it and it may as well not be there.
Under hard acceleration there is little or no vacuum in the inlet and again the valve is closed and doing nothing.
Coming down a hill with the throttle shut using the engine to brake there is a huge amount of inlet pressure, the valve is open and just like at idle air can flow in one direction only from the air box to the exhaust.

What are they for ?
In order to pass tighter emission standards manufacturers of small bikes started fitting catalytic converters to the exhaust on carburettor equipped bikes. But this created a new problem, the catalytic converters would become blocked or contaminated very quickly reducing performance and increasing emissions. By bleeding fresh, oxygen rich air into the exhaust the excess fuel leaving the exhaust could be burnt off before it got to the catalytic converter. However a one way valve was needed to make sure the air only entered the exhaust and only at times when there was repetitively little exhaust pressure such as at idle and closing the throttle to slow down. That's it, it is just a one way valve designed to give your catalytic converter a longer life.

Removing them and blanking them improves performance, right ?
No, not at all, not in any way.
They are closed and doing nothing when you accelerate.
They are closed and doing nothing when you are flat out.
They help keep the exhaust system clean when you are at idle and slowing down.

Are there any reasons to remove them ?
They are ugly , so this might be a reason to remove them.  However if the exhaust is standard and it has a catalytic converter fitted removing the AAI will almost certainly reduce performance after a short time. If the exhaust is being changed to an after market system with no catalytic converter it would be safe to remove the valve and blank off the hole in the exhaust port but only as a cosmetic measure. Removing the valve will make not a drop of difference to the performance.

They can also be problematic, if the valve fails where the vacuum from the inlet manifold opens and closes the valve there can be too much air entering the manifold from the air box making the mixture very weak. If the one way part of the valve fails exhaust gas can indeed be sent to the air box causing all sorts of running issues, melted pipe work or even a melted air box, so again this is a good reason to remove it along with the catalytic converter.

On some bikes (I only know of one) they are always on, there is no link to inlet vacuum and they flow air from the air box into the exhaust even under acceleration and flat out. These can remove so much air from the air box that there is not enough left for the engine leading to very rich running. These should certainly be removed or restricted to flow less air.

A general note about catalytic converters.
Any condition that causes abnormally high levels of unburned hydrocarbons—raw or partially burnt fuel—to reach the converter will tend to significantly elevate its temperature, bringing the risk of a meltdown of the substrate and resultant catalytic deactivation and severe exhaust restriction, hence the addition on extra air to react with the unburned fuel before it reaches the catalytic converter
But your bike may not have one.  The manufacturers or importers should be able to say if your bike has a catalytic converter. The cheapest and simplest catalytic converters are mounted in the front pipe before the silencer, it's normally easy to spot these as the pipe will increase in diameter slightly just before the silencer and it will look obviously like something had been added. However they can also be hidden in the silencer itself which makes them impossible to see from the outside.