Basic Old Method & Stories
1. EX-5 normally has no factory fitted system, but at that time got Hi-Cam as mentioned by Joeker .. most people go for aftermarket engine modification as, EX-5 cannot be done alteration at the "ENGINE BLOCK" .. they fit NTN racing bearings and also HRC Hi-Cam and racing rods. Done also seom modifications to shorten the piston play by levelling the EX-5 head. Also headers / manifold taken from Yamaha RX-Z.
Also the carburator received from Yamaha TX-R150 Panther or Gamma with MainJet setting 225 and PilotJet 100 or 75. Due to some mechanics are not experienced into modifying the TX-R150's carburator, they choose alternative like using Honda CG125's carburator which easily fits the EX-5. The secret of modifying EX-5 also the carburator outlet which heads to engine block, the outlet aluminium piping which lets fuel into burning. Mostly they choose using older model EX-5 because the piping gap is big. Boon siew later on reduced the gap to restrict the EX-5 speed.
The head piping numbered from 1,2,3 and 4 for the final model released. The number 1 and 2 is the most prefered by EX-5 tuners.
2. RX-Z and TX-R150 Panther is the most tight competitors which in some older racing method denies of racing RX-Z and TX-R150 at the same level. This is because TX-R150 Panther (especially "Jerung" in Pasar language due to its physical look of fairing or suppose it should be called Thailand model).
These models are commonly released under Plate number BD* and WC* series which the Selangor variant registered ended at BDS and Wilayah Persekutuan Kuala Lumpur variants ende at WCV .. this is due to ban under certain circumstances by law. It is because the model, can reach stock top speed of 220km/h without any modifications done. Later models of the TX-R150 Panther was not successful. They brought in TX-R150 Gamma series to the market. Suzuki received a big slap after ban of the TX-R150 (Panther /Thailand Model). A good settings on the block intake and outlet using correct measurement (which im not going to reveal here). The codename used by mechanics are"Tengkorak" design. Also the part of "Reed Valves" replacement from PVC to Carbon style improved the airflow to engine block and compression level into the block which receives very high pressure and correct manifold choosing improved sound and power output.
Most people prefer TX-R 150 because the engine is NOT easily "HALT" .. this is not for RX-Z which could "HALT" and the crank will stop permanently, which resuly in pulling down the engine for servicing. As experienced top speed of near 255 to 275kmh can be reached on a fully modified TXR-150 and 215 to 250kmh on RX-Z125 bikes which can be a demon to some riders. Often heard most riders meet fatality on these excessive speeds which the bike can handle.
3. Kawasaki 150R (KIPS) model, which factory fitted with K.I.P.S system elaborated as Kawasaki Intergrated Power-valve System and also the water coolant system makes the motor .. very powerful at its stock level. KIPS produces as the same production of Yamaha TZ-M150 (A road going design of Japanese version TZ-M250 sportbike). Both Kawasaki 150 KIPS and Yamaha TZ-M150 YPVS received this super valve play system.
Yamaha's system known as YPVS (Yamaha Power Valve System) as the same technology used in Yamaha TZ-R250 Street Bike.
Altough many rumours and proven record shows that the most scariest and highly tunable record goes to the TX-R150 engine series. RX-Z125 is not forgotten as the tight competitor on the road modifications done.
Have a good motoring s above was from my past experiences with the bikers, at that time, we were not rempits, but we do respect road users. I dont know what has happened nowadays, all things are upside down and BIKE culture is worst!
Cheers!