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Over the last few years, the popularity of twin-shock trials has increased very noticeably, to the extent that the later and more competitive machines are often now being sold for more money than they cost when new! Unfortunately when it comes to old trials machines, there is little useful information available concerning any of the  worthwhile modifications and upgrades, that can be carried out in order to improve machine performance in modern day competition.

This being the case we have decided to provide some accurate  general guidelines relating to this process, which may well be of assistance to anyone who might be confused about making alterations to their bikes, and who wants to know more. The upgrade process is something that in some cases merely entails replacing worn out OE parts, but can become a lot more involved and costly, depending on what might be required of the finished bike.

However before considering any of what what we have outlined here it is worth remembering that to carry out any upgrade work properly can be quite costly, if you are paying someone else to do the work, and that most completely stock T/S machines will be perfect for use in  club level events, or by riders who are not particularly competitive, and are happy to ride less capable machinery. Concerning upgrades we would urge anyone interested in carrying out modifications, to try and arrange a ride on a bike which has already had similar work done, as what suits one person perfectly, might be far from ideal for someone else!  

Modification/upgrade guidelines

Classictrial modified 240 Fantic

Classictrial modified 240 Fantic

Click to enlarge

Chassis alterations:

Back in the 1970s, when the basic designs of most of the TS machines around today were first used, the very acute turns common in competition today, were very rare. This meant that the old TS bikes were not particularly suitable for use in very tight conditions.......... but as sections were not comparable to those used now, this wasn't much of a problem!

However many classic events today, also include classes for modern machines, which can very easily contend with this very tight going, and even in events which don't include modern bike classes, this type of section is far more common than it was when the old TS bikes were new. Some machines such as the rear kick 200 Fantic, cope very well with these conditions in stock unmodified form, but many other bikes handle poorly, due mainly to their lack of front wheel traction.

Modern machines are generally designed with weight of the bike distributed 50/50 between the front and rear wheels, and also have a quite low centre of gravity, which aids stability and makes the bikes a lot easier to ride. Older TS bikes are often designed with 60% of the weight on the rear, and due to high footrests and far heavier component parts than used on a modern machine, the centre of gravity is also higher up, which makes for a rather cumbersome feeling bike, with little front end grip.

The positive effects relating to handling and feel, that can be achieved through making very simple and fundamental changes to otherwise entirely standard TS machines are in some cases very noticeable. A case in point is the 300 Professional Fantic, whose handling in stock form is very clumsy and ponderous, with not much front end grip.

In real terms altering the steering  angle increases front wheel traction, and is something to be considered by anyone who feels the steering of their bike is vague, or imprecise, and is looking for better handling in many situations. This is especially relevant in the case of 4T bikes such as the TLR Honda, which tend to push the front end out on tight turns, if they are still using the standard geometry.

Relocating the footrests obviously alters the centre of gravity, but care is required here as moving the rests too far back can negate the positive effects of increased front wheel grip provided by a steepened head angle, by putting the extra weight bias you have just added to the front wheel, back on the rear wheel again! On some machines such as the TLR250, which in standard form are much too light on the front end, simply lowering the rests is often all that is required.

Rear suspension geometry can be usefully modified as tyres and the suspension units themselves have improved tremendously over what was around in the 1970s, and subtle changes here result in far better rear wheel grip, and smoother more controlled suspension action and feel. On machines where the top suspension mountings are intrusive, in some cases these can be moved inwards slightly, which is something that makes a noticeable difference to the feel of a properly modified bike.

Front fork action on many machines is compromised, simply due to the fact that springs which may well already have had 30 years of hard use, are still fitted, and that properly designed replacements of the correct dimensions and spring rates, are often very difficult to find. We have very successfully fitted linear springs intended for small capacity early Japanese MX bikes, which in combination with simple mods to damping mechanism, and alterations to reduce seal stiction, mean much better action on most older forks.

A very useful alteration is adapting stock fork yokes to accept fat bars mounted well forward of the steering axis, and is something that will improve any bike, as this tends to quicken the steering, and at the same time provides much better feel. Bikes with “tiller” yokes (bars mounted behind the steering axis), will benefit especially from this update, as steering feedback is particularly poor on all bikes with  these tiller yokes fitted.  

Finally in relation to chassis alterations, we are now using a very  useful chassis set up program, which allows us to look at the likely final effects of any changes made, before actually making the alterations themselves. This program is something  that while not being essential by any means, really does help with getting things right first time on machines we might not have modified  before, and of course is easily able to provide comparative information relating to several different machines.   

Classictrial 240 Fantic

Classictrial 240 Fantic

Click to enlarge


Unfortunately many people with older bikes might mistakenly think that a well worn motor, that has been neglected for many years, can be magically returned to as new condition by simply changing some jets in the worn out OE carb, or maybe changing the crank seals! This is simply not the case, and a motor in poor condition must be properly rebuilt before looking at anything to improve its performance.

On 2T bikes performance can almost always be increased by properly cleaning out the complete exhaust system, and de-coking the exhaust port itself at the same time. The only wholly successful method of removing years of carbon and unburnt oil from a 2T exhaust, involves cutting exhausts which are not re-packable open, cleaning out and then welding back together. Subsequently running the bike on 70:1 fuel oil mix, using a good fully synthetic oil, will mean much better performance, and less carbon/unburnt oil in the newly cleaned out system.

Any 2T bike originally fitted with an old style round slide carb, can be easily improved very noticeably through simply replacing the often badly worn and inefficient (even when new!) carb with a more modern flat slide type. However buying a carb from an Ebay seller, can result in less than ideal running, as well as no technical support or spares back up. Classictrial can supply OKO, Keihin, and Mikuni carbs for several more popular older bikes, and can help with properly jetting bikes that we have no application data for, as long as they can be brought to our workshop near Southampton.

Production constraints, and obviously matters relating purely to cost very often dictate that parts such as air-boxes, were merely functional, and  did nothing much to enhance the performance capability of the engines that they were fitted to. We have found that increasing air-box capacity, and fitting a modern type filter element is a sure way to get better performance, as well as improving  reliability through the use  of a properly fitting modern filter element.

Design of some aftermarket exhaust back boxes, seems to be something that is dictated more by cost, then anything to do with providing a product that actually works. This being the case we have  designed an alloy exhaust back box for Fantic that works very well, and as the shape is very close to that used on the 300 Professional, also provides an original style appearance. In other cases MX back boxes, that can often be found for very reasonable money on Ebay, can be easily modified to suit many applications, and will work well.

Fine tuning of a motor is something that is very often overlooked, but it is quite easy to end up with a bike that is otherwise perfect, but may be very unpleasant to ride, due to something as silly as the needle clip being one groove away from the correct position! This point cannot be empathized enough, and we would urge anyone with final set up problems to take the bike to someone who knows exactly what they are doing, rather than looking for advice from sources which may well not be particularly accurate or helpful.  

* Finally please remember that all of the above information is provided on the strict proviso that any modifications or changes not carried out specifically by Classictrial, are not guaranteed or warranted in any way, and are entirely the responsibility of the individual carrying them out, and that Classictrial are not responsible in any circumstances for  damage or injury, that may occur as a result of poor workmanship. *

Fantic clutch lightener

Fantic clutch lightener

Click to enlarge