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Tech Tuesday: Rotax Max Jetting and carb setup


If you have an EVO, you need to read our Rotax Max EVO article.

There are several different brands of software available like the Jet-Tech Max program that can really help save a lot of time when you go to the track. However the software needs to be calibrated to your engine and carb. That is when you need to have a strategy and become very familiar with the signs that indicate the correct rotax max jetting. These signs can be the plug colour, the dryness and colour of the piston crown and the exhaust header. If the main jet is correct, the plug will be light brown in colour and the piston crown will be dry with a dark brown hue. The engine should also be reaching maximum revs at the end of the longest straight. Using the base settings on a software such as the Jet-Tech Max program will get you close to the correct jet. It then takes several practice sessions to find the correct jet and calibrate the software to the engine.

To choose the correct setting for the needle takes a little effort from the driver who really needs to give good, consise feedback to the mechanic mechanic and needs to be objective and honest about how the engine is performing. It also requires  disicipline not to waste a valuable carb development session just to chase someone else around the track in the heat of battle, try and get yourself some space. As the needle has most influence between 1/4 and 3/4 throttle, the driver needs to focus on how the engine is performing out of the corners. It’s best to keep it simple, pick one corner on the track and get a feeling for how the engine pulls out of that corner. Getting the fastest exit on the best line is not the point of this test, it is to try and optimise the needle setting so the engine pulls strongly and cleanly down the straight.

Jetting affects the amount of fuel mixing with the air

It is a good idea to start rich by lifting the needle up to its highest position. Because the two stroke engine is not very efficient lower down in the revs due to the design of the pipe, the cylinder can be insufficiently scavenged which means a fresh charge of air and fuel is then mixed with exhaust gases. To help overcome this problem the engines typically run a lot of ignition advance to help get the air/fuel mixture burning a little earlier in this dirty environment. If you lift your needle up so you can richen the mixture and make best use of all that ignition advance you may well feel quite good gains in bottom end torque.

By repeating the procedure of going out and feeling how the engine pulls from 1/4 to 3/4 throttle, and then coming in and changing the needle position, the driver can get a good feel for what setting is best. The driver could also try accelerating from different throttle positions on the straight, say from 1/2 to 3/4 throttle, to help evaluate how each needle position effects the performance. To confirm what works the driver could then focus on his line through a portion of track and use split times to see what setting is quickest.

A short note on needles: the K27 and K98 needles have slightly different profiles. The K98 has a steeper taper which will have the effect of richening the mixture ever so slightly above 1/4 throttle. It would take a good driver to notice but the difference would become apparent on a dyno.

Clip Positions on the K98 Needle

You may ask why does anyone need jetting software if they can just go out and feel how the kart is performing? After all that is what every karter did before laptops were common at the track. The truth is that setting up a carb correctly can often be very time consuming and sometimes frustrating for everybody, not just the beginners. What jetting software does is act as a time saving instrument that once you have put the hard work into calibrating the software to your engine and carb allows you to go to the track, plug in the figures from a weather station to the computer and be very very close if not dead on the correct jetting immediately.

The beauty of a program like Jet-Tech Max is that it will take into account things like your choice of floats and idle jets and has features that allow you to easily fine tune to a high degree how close the software will be to the actual needs of the engine. One of these features is called Flow Bench which is a quite advanced adjustment that, according to the developers of the software, is best left alone until the driver and mechanic are quite experienced and confident with how well matched the software is to the engine, as it is a very fine adjustment. It is also possible to set the program up so that you have database settings for several different engines and carburettors, even if they are spread among the range of Rotax classes.

One other feature of the software that adds value is the sheer amount of supporting information included in the package, such as a wide range of chassis setup guides from the manufacturers, as well as driving tips, carb preparation guides written by the developers of the software and official Dellorto and Rotax guides to the engine and carburettor. If you can absorb all that valuable information and put it in to practice then you are well on the way to be a winner!

Alternatively, You can also use this chart to help with your jetting


Like this article? Then read more Tech Tuesday here:

Tech Tuesday – Karting Tools App

Tech Tuesday – 5 Toolbox Tools

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The Max Column

The strength of the Rotax Max engine has always been one of its greatest marketing tools.

As the Rotax classes became more and more competitive, so the Service Centres became more concerned with the life expectancy of internal components.

It is true to say that most Service Centres would rather change components and give a warranty on those parts, than take the risk of any failure that they might be held responsible for.

In reality there are many main bearings and connecting rods that are changed as a precautionary measure. The piston is easier to see and measure whether it is worn.

I am constantly amazed by the number of older engines that still bear the same seal fi?ed when new that have done countless hours and remain reliable and fast. Last week we rebuilt a year 2000 engine that had never been serviced from new. Having run it in we were surprised to see that it had horsepower equivalent to a current delivery unit. It was just the power curve that was less user friendly and might require more accurate carburetion to be fast. However there is no doubt that this particular engine has not only stood the test of time but also remains capable of winning in the right hands.

The reason that I write this is as a sequel to last month’s column where I was extolling the virtues of upgrading your Rotax by trading it in. There is a real option to ask your friendly Rotax Service Centre to give you an options quote to rebuild your existing engine to a similar specification or performance to a new replacement and then compare the prices so that you may make the right and informed choice to suit yourself.

If your accessories include a favourite Carbure?or or Exhaust, then the rebuild cost of your existing engine is very likely to be viable in spite of the generous trade in offer as detailed in last month’s column.

The Rotax EVO upgrades are very likely to be available for use in the UK next year pending the agreement of the MSA. The good news is that there is currently li?le if any overall performance advantage to the EVO over the existing MAX.

Another rumour to dispel is that the EVO is a replacement for the MAX. This is definitely not the case, the Rotax MAX is still and will remain the same core engine, EVO is a range of changes to accessories to make the production item more consistent in terms of quality and performance ex works. The UK market is one of the most highly developed distribution zones in the world for Rotax MAX engines, it is therefore a tall order indeed for the EVO accessories to out- gun existing good engines.

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The MAX Column


JAG Engineering have launched a Buy-Back scheme for any Max owner who is looking to upgrade to a new engine.

Any Rotax Max engine that is in working order and has a JAG seal will a?ract a trade in value of £550 for Seniors and £525 for Juniors.

The scheme is available through the Rotax Approved Service Centre network. Who will then overhaul the traded in engine to reintroduce it to the market for newcomers or Club racers. These rebuilt engines that will carry a full warranty as usual on all the new parts fi?ed.

There are so many perfectly good engines out there in use today that have never been apart, this
is a real opportunity for existing customers to upgrade their equipment at a really good price. Effectively a brand new engine for li?le more than a major rebuild. Equally the new engine and accessories will be covered by the Rotax Warranty Scheme as usual.

This offer is open to both existing “Pre-EVO” engines and the new EVO which is fully anticipated to be introduced here in the UK next January. The trade in deal will not affect the introductory price on EVO upgrade kits. The trade in is for engines complete with all their accessories. If you wish to keep any of these, such as a favourite Carb or Exhaust then you have can remove the new item from the accessory box or pay for it.

Although the EVO is due to come to UK racing next year there are no plans to obsolete any of the existing spec. In other words it will be perfectly legal to race “Pre-EVO” in the same classes as the new EVO Junior and Senior. Minimax engines won’t change specification to EVO in the UK for the foreseeable future. Our Minimax class and specification differs from the BRP-Rotax version. We do not wish to affect the stability of this excellent class as the first step out of Cadets.

In future it will be possible to introduce replacement accessories as the old type cease production, the exhaust system for example. At present the existing pipe is still in production, the new EVO pipe has a different construction. Initial tests confirm that there is li?le or no difference between new and old in terms of performance. However the new type with dismountable silencer is certainly easier to scrutineer. It’s an example of how a staged introduction of some components could benefit the Rotax classes without end user cost penalties.

Karting was late to be affected by the economic downturn and to be truthful the sport has been slow to recover. The good news is that taking Independent Kart Racing events into account the sport is

in be?er health than ever. Strong grids in the Rotax classes and very good numbers in Cadets can only be good news for the future. I know some Clubs are using their IKR as a first step to MSA racing..

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Rotax Electrics Explained



The vast majority of Max engines across all their classes are used by Club level drivers that keep the same unit for years and have it serviced annually. The market for these products remains the strongest single product that the sport of Karting has ever seen.

New parts are covered by the unique BRP-ROTAX warranty. There are however many regular maintenance tasks that can easily be completed by the owner, mechanic or friend. These are the items outside the sealed engine unit, especially the Rotax electrics which just require a little regular attention to ensure that reliability and performance remain at the top of their game.

The Battery is the heart of any electric start vehicle it should be kept clean and regularly recharged to keep it in good condition. The Battery support must also be in good condition with the foam insulation material properly in place to protect against vibration. The battery connections need to be tight to give a good supply of current. Care must be taken to ensure that the charging Jack plug cannot earth to the chassis. I see so many of these just loose and close to a metal earthing point. If the centre electrode can arc to earth it is an almost certain ignition pack replacement. A completely avoidable expense. You can bet your life it will happen within sight of the chequered flag!

The wiring loom can also do with a check over and clean. If you do this regularly and that means taking it off the chassis, you will find any chafed areas or connectors that could do with repair. Repair to the wiring harness is allowed within the regulations but not modification. This means that you may replace a damaged connector or change the spade terminals on an old style loom to the new ring type, however you must not significantly shorten the cables. If the harness is worn through you need to decide whether it can reasonably be repaired or does it really need to be replaced in order for it to remain dependable.

If the Starter Motor gives trouble I would recommend that you take it to a Service Centre or replace it. The unit is very good but once it starts to play up it can only get worse.

The Switches are very good and seldom cause a problem, it is important for them to be carefully handled and sited, the cables to them should not be under strain and always remember the two big wires go to the big button!

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Rotax EVO Engine – the facts

Following the announcement of the Rotax EVO engine upgrades there has been much speculation and opinion flying around the Karting World. BRP-Rotax have never introduced any changes that completely obsolete previous production engines or components. The Rotax Max EVO range of engines is designed to be the basis of future production for the next 15 years. The MAX has already enjoyed a unique level of success for fieen years. With the inclusion
of modern technology the EVO has a brought new features to Kart engines never seen before.

The new Dellorto electronic ignition system allows for improved ignition performance and an electronically controlled Exhaust (Power) Valve on Senior and DD2 models. This will ensure the constant and controlled opening and closing of the Exhaust Valve without any influence from the Exhaust system itself. This won’t improve the ultimate performance but it will greatly improve the engine’s ability to perform consistently. By the same token the new ignition system will improve the ignition curve to help the engines combustion to perform more consistently. This will work with the new specification VHSB 34 XS Carbureor which is a complete rethink on the existing QD and QS carbs in use today. The new carbureor has a similar body
and a 12.5 Venturi. However an old type QD or QS cannot be upgraded to XS specification. If you want to get the right Rotax Max jetting then click the link

The internal machining of the body is significantly different. The factory have done extensive testing to arrive at the new specification which allows for consistent performance with very lile variation to jet sizes. The new carb will run with a jet around the 125 mark. The need to change jets will be reduced to almost nil. Due to the time of year when the EVO range was introduced, JAG Engineering and the MSA agreed that the best time for introduction into the UK market would be 1st January 2016. It was decided that for maximum stability it would be beer to hold off until 2016 to allow for the products to sele into the European market and minimise any on cost to customers.

BRP- Rotax have pledged to supply MAX COLUMN existing pre-EVO engines and accessories for the foreseeable future, it has also been agreed to supply upgrade kits at subsidised prices for those wishing to convert their engines to use with EVO accessories. There is no hard evidence yet that the Rotax Max EVO engines or upgrades
 will in fact be faster. Yes they have the potential to be easier to use, easier to Jet and use less fuel, but faster? The jury is definitely out at the moment. The delayed introduction in the UK is the best possible solution for our extremely strong customer base. This gives us plenty of time to do dyno and circuit testing to truly evaluate all the changes and how to stage their introduction into the market.

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Rotax Regional Championships

The new season is upon us and for the first time there will be Rotax Regional Championships taking place at a Club near you. There are five regions in total covering all the main catchment areas of the UK Mainland. The Scoish and Cumbrian will be based around Larkhall and Rowrah. The Northern will be Fulbeck, Wombwell, Wigan
and Hooton Park. The Midlands is represented by Kimbolton, Shenington, Whilton Mill and Little Rissington. The South West includes Llandow, Dunkeswell, Clay pigeon and Forest Edge and last but not least the South East is hosted by Bayford Meadows, Buckmore Park, Hoddesdon and Blackbushe. The idea is that drivers must belong to a club in their local area and aend a designated race meeting at each of their area clubs.

The participating Clubs in each area have been chosen
to avoid any clashes. Each regional Championship will only have a maximum of four events. At the end of the series there
will be a regional Champion for each and no national level travel required. The hope is that this
will encourage drivers to sample other tracks relatively local to their homes, thereby cuing the cost of good quality and varied racing to a minimum. School age children are encouraged not to attend Friday practice during term time and will be offered a good share of the Practice time on the Saturday. It’s hoped that participating clubs will add a sense of occasion to their Regional Championship weekends by offering a BBQ or Hog roast on the Saturday night.

All the Rotax classes will have
the opportunity to compete; Minimax, Junior Max, Senior Max, Senior Max 177 and Max Masters. It will be necessary to register for the Championships but there will be no fee. Dates
will be published in the very near future, most clubs have already committed to a date. The Club meetings will be run exactly as normal when hosting a regional round, their only responsibility is to submit their race results to JAG Engineering aer each event. JAG will then collate the points using a common system across the board to ensure equality and fair play. The host Clubs officials will not need to change their role in any way. It is hoped that this new initiative will help to nurture entries at some of the less well supported clubs and support the new growth in Club level racing. Rumor still persists regarding the introduction of the Rotax EVO engines. This will not happen until January 2016 at the earliest. No EVO components will be eligible for use during 2015.

Decisions have yet to be made for the British and Irish markets, we are fortunate indeed that there will be EVO usage in Europe this year, which will give us the opportunity to learn from that experience and keep existing engines competitive and valuable.

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Rotax Driving tips

The art of driving a Max powered kart is always made to look easy by those who are really good at it. Much like any sport, the people at the top appear to apply the minimum of effort to achieve what looks to be impossible.

There is usually one common thread that helps to unravel the secret. They all, whatever their chosen sport, spend a lot of time doing it! It really is a case of practice makes perfect. Most top drivers will seldom admit to doing many perfect laps, every lap is a compromise in some way. Starting from the beginning therefore it is important that your Kart is in good condition and assuming that your initial level of knowledge is slight, it has to be a good idea to have your chassis professionally set up to ensure that it is all true and safe. A slightly bent chassis or misaligned steering can make any Kart really hard to drive but the less experienced will often assume that all is well and drive around an inherent problem. There is no need to make life unnecessarily difficult. Now that we know all the wheels are pointing in the right direction and that the brakes and steering are safe, the time has come to get out on track and start enjoying your Karting.

If you are really new to the sport, most clubs will have an onsite ARKS (Association of Racing Kart Schools) examiner. This guy maybe very busy, but his role is to make sure that as many newcomers as possible pass their test and start racing as a regular club member. This does not mean to say that the ARKS test is a walk in the park, but it does apply a set of guidelines which the driver needs to achieve before being allowed out in a race. The ARKS examiner is a person worth meeting, he will be sure to give good basic advice and help introduce you to others that have first-hand knowledge of your local circuit. If you are new to the sport or the circuit it is a good idea to get to the track early, get yourself ready and go for a track walk. Make sure with the officials that the track is open for you to walk round and if possible ask someone with local knowledge to show you the lines, braking points etc. Once you’ve been to the circuit, a walk round loses its value very quickly, you’ll subconsciously remember the circuit and will be on the pace after a couple of warm up laps.

1When you go out onto the circuit keep some space around you and don’t get too close to others that may involve you in their accident. There is not much point in spoiling a potential new friendship by crashing into them. As you drive onto the track remember that the tyres will take at least a lap before they have any predictable grip. Please do not leave the grid with a flamboyant full throttle wheel-spin only to disappear into the bushes at the first corner. This happens at every club meeting every weekend of the year, just don’t let it be you! Having warmed yourself, your engine and your tyres, now is the time to start applying a bit more throttle and start enjoying Karting for what it is, probably the best form of motor sport in the world! Concentrate on being smooth with all the controls, squeeze the accelerator down and brake firmly but smoothly without locking the wheels. If the Kart is correctly set up it should slow in a straight line without snatching to one side or the other.

The best early advise is try to get your braking done in a straight line and only accelerate when the kart is well turned in to the corner. It could be said that acceleration should only begin past the apex, but in Karting, even at an early learning stage this is really too late. The whole idea of a Kart is that the chassis is the suspension and the live rear axle has to rely on the driver making best use of the extraordinary handling capabilities of a kart. The transition between braking and acceleration is a real balancing act and probably the most important element that defines a fast driver from an ordinary one. At first my advice is to take it easy and explore your own limitations. It is very likely that you will soon find that you are catching some others up as well as learning from those that overtake you. Wrap up warm, it’s still good fun in the winter!