When you decide to tune your Runner there are dozens of parts and kits to choose from. Here I will outline the types of parts available, what they do and where to get them. Malossi, of coarse are the main manufacturers of scooter performance parts with Doppler and Polini being other large suppliers. If you can't find what you want to know here then e-mail me and I'll be glad to help if I can.

PISTONS/CYLINDERS: Being the place where most power gains are available I thought it a good place to start. There is a long list of modifications which can be done to the piston/cylinder including polishing, porting, boreing etc but many of these procedures are labour intensive and reduce the reliability of the machine. 2 Of the main and easiest ways to gain power are to increase the capacity of the cylinder or to increase the compression it is capable of producing. By far the most reliable method of increasing the capacity of your Runner is by Fitting a Malossi 70cc kit to the 50cc or the 172cc kit to the 125/180. A 70cc kit should give an extra 2-3hp on a fully de-restricted 50cc. The 172 kit however offers a full 6-7 hp extra when fitted to the 125 and 1-2 hp with the 180. The 172 kit also increases the compression ratio from 9.9:1 on the 125 and 9.8:1 on the 180 to 11:1. The compression ratio can be increased further to approximatly 12-13:1 by fitting a high compression cylinder head such as is available from PM Tuning however such a high ratio would not be suitable for every day road use due to the decrease in reliability. Both the 70 and 172cc kits come with all nessassery parts required, e/g rings, gaskets and carbon reeds. When fitting these kits, however, you must use a high quality fully synthetic oil and the use of super unleaded 98 octane fuel is also reccomended. 

CARBS: The fitting of a carb. kit, the most common and most suited to the Runner is the Malossi/Dellorto 25mm carb although Mukini also do a 24mm carb, Will generally increase hp by just 1 but will offer a vast increase in throttle response allowing for lower acceleration times when moving, e.g 30mph-50mph. Again the kits come with all parts requires for fitting. Further improvements can be made to the carb. such as as fitting a performance air filter and increasing the main jet size to match. This will allow more Fuel/air into the engine and therefore allow it to burn faster. Approx 0.5hp is available by fitting the filter and correct jet. For the 125/172/180 as size 100 jet used with a Malossi 'red' filter appears to work best although differend filters, there are several available, will require different jets. PM Tuning also offer further modification to carbs such as 'D' shaping which will further increase performance.

CRANK: The fitting of a racing crank is a must for any tuned engine as the extra power puts alot of strain on the standard crank. As well as being much more durable a Malossi crank allows a highr primary compression allowing slightly more power and a higher rpm celing(16000rpm). A tuned runner engine will only rev as high as 9500rpm-10000rpm as long as the standard CDI is left in place. Well below the maximum for the crank and therfore allowing a long life from the crank. Piece of mind is another reason for the racing crank as if the standard crank fails, especially at high speed, it is likley to cause serious damage to the piston, cylinder and crankcase leading to hefty repair costs.

BOOST BOTTLES:A Boost bottle connects to the inlet manifold of the carb. and increases throttle response by storing air/fuell mixture from the carb when the throttle is released which can then be instantly injected when the throttle is opened up again. It can only be affective, however, when placed as close as possible to the manifold. Again Malossi produce a boost bottle but in this instance the polished alloy Doppler bottle performs slightly better.

VARIATORS:A performance variator can increase speed and acceleration by allowing the power to be put throught the transmission in a more efficiant way. This is achieved by the precisly sloped slide surface, the lighter(alloy) material used together with the roller weights. A full kit will have all the parts set up to work perfectly together, e.g rollers and torque drive spring. It is possible to change the roller weights in a standard variator to achieve different performance charicteristics. Lighter rollers will allow quicker acceleration and less top speed while heaveir rollers allow more top speed and less acceleration. Malossi and Polini make two of the best kits for the Runner at the moment.

BELTS:Kevlar belts help to allow more power to the rear wheel by elimination a large amount of the flexing and streaching that standard belts can suffer from. On a stock engine/transmission little difference will be achieved other then a longer life but when used with performance variator kits the belts, mated to a high power engine, will have the ability to put the power down more efficiantly

EXHAUSTS:Performance exhaust can be one of the most difficult tuning items to choose as they are the most numerous item available, PM Tuning, Polini, Scorpion, S.I.P, Kundo, Leo Vichi and Malossi are among some of the manufactures producing exhausts for the 125/180 and the list of names is endless for the 50cc. For the 50cc a performance can serve to de-restrict the motor as well as add a little power but for the 125/180 a performance exhaust should be near the end of your list as the standard exhaust is an excellent unit. You can tune the 125/180 motor to a high degree, i.e 172cc, 25mm carb, crank etc before needing a sports exhaust and once you do get one you will be lucky if you get much increase in performance as, despite what most exhaust manufacturers will tell you, changes to roller weights and carb jets/needles and sometimes reeds will be needed to obtain optimum performance. A rolling road would be ideal but without one you'll just have to play with different settings to get it right. 

GEAR KITS:Gear kits or gear up kits will lenghten the ratio of your runners gearing allowing a higher top speed. They should only be fitted to a bike which has had a larger piston fitted(70cc or 172cc) otherwise the motor will not have the power to pull the gearing and will have poor performance. Fitting a gear kit to a 70cc runner can give a top speed of up to 70-80mph with tuning and a 172cc can achieve over 100mph again with further tuning. However if your preferance is acceleration for city/traffic riding then a gear kit may not be for you as lenghtening the gearing reduces acceleration. e.g a 70cc runner with out gear kit may only be able to reach 60mph but acceleration will be rapid the same way a 172cc will only be capable of 85-90mph but acceleration, especially with standard 125 gearing is explosive. I have found that leaving the standard 125 gearing and using a Malossi multivar 2000 with 15.5gr rollers allows for a 95mph top speed while keeping the mentle acceleration. If ,however, you use your Runner mainly for motorway use a gear up kit is a better choice as it allows the engine to reach higher speeds at lower rpm therefore reducing strain/wear and tear.

CLUTCH: The clutch controlles how progressivly/quickly the engines power engage the rear wheel. A standard cluch is quite capable of taking the power of a tuned engine in everyday use. Where race clutches really come into their own is for track days or 1/4 or 1/8 mile sprints, where standing starts are important.Using springs of differents strenghts can improve the performance of a standard clutch by allowing it to engage more quickly(using weaker springs). A full racing cluch will generally have springs calibrated to the engine and will have a smaller area of clutch lining allowing the clutch engage more rapidly while not bogging the motor down at higher speeds. Some competition clutched, however, are not suitable for road use as they have a 'light switch' affect which can actually be dangerous especially in the wet. Malossi have begun to produce their 'Delta' clutch for the 125/172/180 to go with the one they already produce for the 50/70cc. PM Tuning also offer a service where they will modify your standard clutch which, they say, gives lightning start times while not bogging the motor at high speeds.


Copyright Paul Loughnane 2001,2002, All Rights Reserved