Upgrade my TY: Why bother?

Upgrades why bother?

This page is intended to provide more information on the various  TY upgrades detailed on this site. Some areas don’t seem to be that well understood and hopefully what’s outlined here will help with that somewhat?

Chassis: At the time when twin-shock (TS) and air-cooled mono (ACM) machines were designed the tyres available were not particularly effective and this led to rear biased weight distribution, generally around 40% front, 60% rear. Indeed, a popular alteration back in the day was to move the footrests back, putting even more weight on the rear!

Today a modern machine’s weight distribution is going to be around 60 front, 40% rear. This has come about as a result of greatly improved tyres and much more compact motors which mean longer swinging arms can be fitted, which help to move the weight forward.

From the perspective of a TS or ACM rider putting more weight on the front wheel is a win/win situation, as steering is greatly improved through better front wheel traction, resulting in a bike much more suited for use in present day competition.

Footrests need to be lowered on TY’s and ideally also moved forwards slightly. This lowers the centre of gravity and moving the rests forward complements steering angle modifications. Moving the rests back reduces front wheel grip and lessens the positive effects of any changes to the steering angle which may have been carried out.

175 frame being modified

The P65 style “tiller” handlebar position is something which was used on all of the TY twin-shock machines and was carried over to the Mono. Control of any bike fitted with tillers can be improved substantially by fitting a modified stock top yoke with bars positioned further forward. Billet yokes are available for some TY models but in terms of function these will not work any better than modified stock, which are less than half the cost.

Induction: Most older trials machines have very restrictive induction systems, which mean compromised air flow into the motor at anything above tick-over engine speeds.  Very restrictive intake and exhaust systems seem  quite common on Japanese trials machines and were very likely fitted to make the bikes gentle and easy to ride for beginners or youngsters. Long convoluted intake hoses are very common and will reduce performance even if the air box has been modified or replaced completely. On a 175 best possible performance is realised using competition air-boxes with a volume of 2000cc or above.

Stock 175 air-box with very restrictive intake hose

On the Yamaha TY twin-shocks induction is an area where properly carried out improvements make a really big difference and can easily transform an otherwise lack lustre poorly performing machine. The intake duct must be looked at as a very important part of your motor, and to work properly air box, induction hose, carb and reed block, must all be improved or changed,  as in the case of the TY175 the stock parts are not very effective in performance terms.

It’s pretty obvious why tiny induction hose’s like those fitted to TY175 are likely to restrict performance, and the same can be said for carbs which are more than 30 years old  4mm too small and invariably completely worn out! Less obvious are the substantial performance gains that a properly designed and made custom air-box and properly set up replacement carb will provide. There are very good reasons for an uprated intake system working so well, but they are relatively involved and not appropriate to outline here.

The Mono induction system is something which MUST be modified or replaced entirely for best possible performance, the main problem area being the stock air box to carb induction hose and reed block assembly. A simple alloy boost chamber will improve a Mono’s running enormously and is well worth looking at if you are wanting best possible performance. A Fantic 305 reed block works far better than stock Mono and fits without modifications to cylinder.

Mono induction upgrade

Exhaust systems: Production exhaust systems fitted to machines designed and made back in the 70s and 80s (with the exception of Fantic), all seem to be intended to slow down throttle response and reduce the tendency to lose traction, which was probably related directly to the less than great tyres around back then?

Most 2T motors respond well to a shorter front pipe with ID no bigger than the OD of the exhaust port itself. These speed up exhaust gas velocity and help to provide increased power and torque at all engine speeds. Making one is relatively easy for anyone who can weld reasonably well, as tube bends are easily available from Ebay.

Original mid and back boxes work reasonably well if they have been properly serviced, but while filling with caustic soda, brake fluid or any of the other methods of servicing an exhaust mentioned on the forums might help in some cases, the ONLY 100% effective way of servicing an exhaust is cutting it open, repacking and welding it back together!

Core sizes of some after-market  trials back-boxes seem to be too small for best possible performance in most cases and fitting a slightly bigger core or adapting an MX back box to fit will improve running somewhat. Exhaust system service is very important for anyone wanting a bike running at its best, but as its not a particularly easy job is very often overlooked.

On the Mono modifying the middle box to Pro-Monty internal specifications is a good idea, as the stock core is very small as is the internal volume of the box itself. For a Mono the DEP re-packable back box with 25mm core and re-packable is well worth a look, and they are very reasonably priced (£64 July 2018).

Carburetion/ignition: Worn out carbs and ignition systems well past their best are both things which adversely affect the running of many older machines. It is not difficult to find new replacement Dell Orto carbs for bikes such as Fantic which are a direct replacement for the worn out original parts.

However, replacement carbs for Japanese bikes are much more difficult, as while they will have been made by Keihin, Mikuni or TK all were custom manufactured for specific applications and have been unavailable for many years. Essentially these carbs were designed to work well with the rather restrictive intake systems, fitted to most Japanese made bikes. Allens Performance can supply a Mikuni carb kit for the Mono, which is a direct replacement for OE. However, a new carb will not improve running much unless the exhaust is new or has been recently serviced!

Various after-market ignition systems are manufactured for older machines and in most cases, these will help improve performance and reliability. However, systems which are not adjustable may prove problematic when fitted to a modified motor, whose ignition requirements often differ markedly from a stock machine. If you have made any significant modifications to your motor, induction or exhaust systems, its probably a good idea to contact the manufacturer of the ignition you are interested in for accurate advice before purchase.

Suspension: This seems to be an area where appearance rather than actual function is more important to many riders? Outdated designs and cheaply made mass produced units which are not rebuildable strangely seem to be very popular currently!

Unfortunately, less than effective suspension means bikes which are far less competitive and more difficult to ride for less able riders. Maxton and Willburs suspension is available for trials machines but few competitors are likely to want to spend rather more than £500 on a pair of trials shocks!

The best possible choice for serious riders is likely to be  rebuildable gas shocks, which are going to work better than cheaply made non-rebuildable units and likely to outlast them 3 or 4 times over . Falcon is a good  suspension choice and their products have been used by top riders for many years .

Falcon Factory suspension for Mono