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Tech Tuesday: 10 ways to get the best performance in TKM

Tech Tuesday: 10 ways to get the best performance in TKM

As in any class that relies on a control engine it’s those last fractions that can put you on the top step of the podium. Yet especially in the case of our TKM BT82, actually finding them is not something that comes from spending piles of hard earned dosh. It comes down to attention to detail.

The whole reason for the existence of the class when it first hit the tracks 20 plus years ago was to provide close racing at minimum cost. No cheque books, just good preparation and of course top notch driving. Part of that thinking the class was designed to operate with the tightest of regulations on the engine to prevent tuning at a time when other classes were struggling because too much freedom meant engines could become redundant in the space of a month when something quicker came out!

But although ‘tuning’ is kept to a minimum within TKM for that reason, there are plenty of small ways in which you can help maximise performance, not by cheating but by perfecting. Most of these tweaks cost next to nothing and can be carried out by anyone with just the smallest of ability. So here we go with 10 areas where you can find time:

TKM BT82 ENGINES 5 edit

Three BT82 Units

1) When is the engine at its best?

In pure performance terms the BT82 has not been modified over its history, The dimensions in the fiche today are pretty much the same as those created two decades ago. However there have been some internal changes which are worth pointing out.

To increase reliability and rigidity, things like the crank main bearings have been increased in size. This doesn’t make the engine quicker but it does mean you can rev it harder for longer.  Several years ago the method of manufacturing the liner was changed from old style casting to the latest computer based machining. So on older engines there will be small variations which can mean one will have a fractional benefit over another. On the latest type engines the machining is to such fine tolerances that everyone should be exactly the same. So you can forget what has happened in some other classes where people pay silly money for engines that are supposed to be ‘special’. You will not find those in TKM. But there are important things that need to be done to maximise what you have.

There are two ways you can purchase a new TKM engine – standard or fiched. If gaining the ultimate top performance is not vital then by all means just take the standard engine. It can always be fiched later. But if you want the ultimate then go for the fully fiched unit. For a Fiched unit Tal-Ko includes extra checking and permitted machining of the cylinder liner top and the cylinder head to give best possible settings. The use of correct thickness base gaskets first puts the cylinder and its ports in the ideal position. Then when the cylinder position is established, the correct head volume and squish clearance is achieved with this machining.

Such factory fiching ensures the engine not only runs fast but also complies fully with the rules. It is also a job that needs to be done by a trusted specialist.  At Tal-Ko that job will cost you around £110 and comes with the promise of a job perfectly done. If someone tries to get you to spend a lot more than they are either robbing you or doing something illegal. Beware! Either way when you get your new engine you need to run it in for around 1 to 1.5 hours to put it through lots of heat cycles and to loosen it all off.

carb

2) Carburettor

This is the place where you will find the most power for the least £s.

Well first let’s just say that cleanliness is vital here so make sure that you have a fuel filter between the tank and carb. One in the tank and another in the pipe is perfect. You need one vital tool invaluable in ensuring that the carburettor is performing correctly – the carb pressure tester. You connect the tester pipe to the carb petrol inlet and then slowly pump up the pressure until the inlet needle valve opens. This pressure reduction is called the “pop off”. Expect the valve to open at about 9-11psi and to then shut at about 6-8psi.  Make sure the valve is free and wet with either petrol or WD40 otherwise it can be gummed and give a silly figure. If the pressure readings are not right repeat several times and adjust by gently altering the angle of the paddle in the bottom of the carburettor.  TKM sell a simple device for assisting with this for about £3.  It is a simple paddle height gauge to give you the correct clearance needed between the paddle and carburettor base for the correct setting.

The pressures you test with this gauge have a direct effect on the fuel/air mixture so it is vital you keep the pressures pretty consistent otherwise your carburation can be seriously affected.

As a rough guide the low jet (the one with a screw head) should start about two turns out and the high one (with the T bar) about half a turn out. And they should always total about 2.5 turns out. Now that’s the base point. Now you need to tune on track. There are some important things to watch for. First, over the first few laps when the kart brakes for a corner and then accelerates there should be some blue smoke coming from the exhaust.  If none then the engine could be too weak. That means it will lose power as the engine gets hotter over a race distance and could cause harm. Richen the mixture by turning the high speed (T bar) out say a quarter turn.

Then the acid test is on the longest straight. The engine should pull hard and sweetly all the way down the straight. If it stops pulling and starts to chortle that’s known as 4-stroking (don’t ask me why!) and means it is too rich. Just wind the high jet in a fraction until you get it clear all the way down the straight.

It is a total myth that weak mixture will make the engine quicker. While it will on some types of two-strokes, the piston port BT82 thrives on being quite rich especially in the mid-range. To check carb settings after a race simply slide off the exhaust with the flex from the manifold and look down inside the manifold. If it is light grey it is too weak. Dark grey/black is ideal and wet black too rich.

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Carb adjustment… Bandit Style

3) On track adjustment of carb

What some people don’t realise is that for optimum performance in a race you may need to adjust the high jet.  If it is very hot it may well benefit from being richer – winding out the jet a little. And ironically sometimes the same applies if it is very cold. Doing this requires some practice to make sure you can reach your hand down to the engine and tweak the high jet those small amounts to fine the perfect setting.

General rule here is half way through a race when the engine is up to temperature simply open out the high jet 1/8 turn plus. This will prevent the engine getting too hot and running slow.  You’ll often see top drivers making such adjustments – that’s what helps make them winners!

FuelPumpsShot

4) Fuel

Two key things here. The TKM engine likes being cool to give best power. The oil in the oil/fuel mix helps keep it cool. Some people think they can gain performance by changing that mix by reducing the amount of oil. It really doesn’t give any extra power and indeed especially in hot conditions could actually lose power.

Second the fuel itself. The BT82 is fundamentality a low compression engine so therefore use of super unleaded is not likely to gain any performance. On the Tal-Ko dyno Alan Turney has not noticed any difference between performance of the two. However if you do choose to use super or are using S1 control fuel then it is wise to make sure you use the fuel in testing just in case it changes the mixture effects.

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Exhause flex covered in heat resistant sleeve

5) Exhaust flex

So that bit of flex between the two is important to be in good condition. It costs next to nothing so make sure it is regularly changed, make sure it is cut straight and always use the flex ring insert available from Tal-Ko, which keeps the flex fully open at the exhaust end where without this clever ring insert the flex can distort and collapse partially blocking the flow.

And then the vital thing is to make full use of heatproof webbing to thoroughly seal it all. Wrapped tight and using twisted steel lock wire or steel cable ties to secure. It will make you go faster and keep the noise down.

Oh and that piece of flex really can make a real difference. Standard length is about 65mm. Longer gives you better low to mid-range performance. Shorter helps at the top end. I’d always advise that longer is better than shorter because the strength of the engine is maximising its low to mid-range performance enabling a smaller axle sprocket to give high MPH down the straights.

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tkm exhaust diagram

6) Exhaust

The exhaust itself can’t make you go quicker but it can make you go slower. When it is new the exhaust is nice and clean inside and the gases can pass through efficiently. But with use it will gradually and inevitably get clogged up with oily carbon deposits. They restrict the space and slow down the gases – and that means you get less power.

You will actually find the exhaust weighs more with all the deposits inside so you can keep an eye on it by use of a very accurate scales. So periodically you need to clean the exhaust out. Health and Safety laws forbid me from telling you what the technique is that many people use to clean it out and to be honest it really is a difficult and messy job. The best (easiest) way is simply buy a fresh new one when your one is past its sell by date.

By the way the other tip here is to keep one exhaust for testing and then have a fresh new one which is only used for racing. Then after a year you throw out the test one and move onto using the race one for testing and buy a new race one.  Simple and cost effective.

BT PISTON AND RING TR

BT82 PISTON & RINGS 100cc 2 TK

7) Piston Rings

First let’s explain something here. Some years ago one inventive engine tuner found there was an advantage to be had by artificially gumming the top ring in place in the piston. It helped cheat the rule on head volume testing. Hence the rule was brought in that the ring must be more than 50 per cent free.

Now in reality you want all rings to be free in the piston grooves to do their job properly. So don’t get caught out with a ring which has become accidentally gummed in the piston To check this, take off the cylinder head and then lift the barrel off the piston. Once you have done that you can easily see if a ring is stuck. If it is then gentle movement of the ring in the piston should help it come free. This must be carried out carefully by easing the ends of the ring until it is fully free to lift it off the piston. Once off you can carefully scrape clean the ring and its ring groove before fitting it back into position. This is also a good opportunity to also fit new rings if required.  Keep the rings pressed in as you guide the piston back into the barrel piston bore. Nimble fingers help!

A nice free ring helps give good all round power and will stop you falling foul of scrutineering.

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Self adjusting or not, go to hard on the brakes and you’ll end up like this fella

8) Brakes

Brakes won’t make you go quicker but can cost you a lot of performance. You want them to work well when you hit the pedal, but give immediate release when you come off the pedal. Even slight binding will cost you a lot of time. Until quite recently the brakes used on karts were manually adjusted and ideal for sprint racing because you could set them up so that there was no fear of binding when not in use. With that type you just need to make sure the brake disc is centrally positioned within the pads and then get the pads adjusted correctly with pad shims or threaded adjuster. No problem.

However more recently self-adjusting brakes have become normal fitment. Using the same principle as on cars, the pads press on the disc when in use and then back off a fraction to give clearance. However it is common to find that they still feel like they are binding a touch. To help overcome this quite a lot of systems now use ‘floating discs’ which have a degree of side to side movement to help reduce binding. But…I’d have to say that even then there is a risk. The best systems have springs to help take the pads back off the disc and should give the best result.

But whatever type you have one thing is vital – the hydraulic fluid and pad seals. You need to regularly drain out the fluid and put in fresh Dot 4 or Dot 5 fluid and bleed as appropriate to the system. And then artificially move the pads in and out a small amount to help ensure they are nice and free. If they are sticking then you must change the pistons and rubber seals and refill, bleed etc.

Jack Partridge

9) Racing in the wet

Three critical things here. First you need to fit a TKM wet box cover over the inlets of the air box. It keeps out the majority of water from the carb intake which is vital in preventing problems with carburation. However even with that in place you need to check the filter after every time on the circuit. If it is wet you need to dry it out using an airline blowing air outwards from the inside. Ideally change to a dry filter. If it is wet it can make the mixture too rich.

Second, the brake disc needs protecting from water to keep up its temperature. Tal-Ko make a ready-made item for its brakes. You can make one just from a cut down number plate.

Finally, if you have the time raise the kart seat an inch or two. Weight at an extra height helps increase grip and is an important way to sometimes find quite a lot of speed when it is slippery.

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TKM regulation Maxxis tyres

10) Tyres

Let’s start by killing one commonly held thought – going flat-out on new tyres will give the best results. No, it works in F1 but they have totally different tyres. With kart tyres it can lose you performance. What counts are heat cycles and if you go straight out on new tyres giving them maximum grief you may well cook them and will certainly reduce their life. Don’t do it!

What you should do is go out on a new set at normal pressure and do just three gentle laps. Then come in and let them cool. Re-check pressure and then you can go out and press them hard. They will last longer and give the longest length of consistent good performance. And…use the pressure wisely. Higher pressures such as 24psi may be needed in the winter to make the tyres work in cold conditions. But in hot conditions it might be 8psi.

It is very important to vary the pressure to suit the conditions. Personally I’d always use a tyre temp gauge to check the temperature of the tyres when they come off the track. Ideally you want about 75/80C as a rough maximum. More than that and you will potentially cause excessive wear and heat damage.

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Written by Grahame Butterworth

 

Like this article? Then read more Tech Tuesday here:

Tech Tuesday – How to read your tyres

Tech Tuesday – Kart Aerodynamics