All the parts used are available through
Scootling. This is a demo model and is not registered
for road use.
11/2003 - current top
speed = 55km/h
It arrived in a thundercloud grey colour, with no
obvious modifications to it. There were a couple
of stickers on the side panels and the body was
in decent condition overall. These ZX AF28s have
a longer wheelbase than the base model AF27 and
AF28 SR Dios, and have the front disc brake. These
models also have different mufflers and richer jetting
in the carburettors. |
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03/2004 - New top speed
= 70km/h
The first modifications made were to the driveline.
It had seen a lot of use and the belt and weight rollers
were well worn. These were replaced, with lighter
weight rollers for the variator, a high speed pulley and a new factory OEM belt. This gave the Dio a higher
launch RPM and keeps the revs higher during acceleraton.
The slgihtly lighter rollers (7.7g) sit inside
the variator pulley in the photo. |
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04/2004
This went well for a while, with no changing of
other parts required. The top speed increased a
lot, thanks to the high speed pulley. This pulley
allows the belt to be pulled to the extent of the
drive face on the clutch, meaning a higher gearing
ratio at top speeds. The paths for the weight rollers
have a reworked profile too, giving a better acceleration
curve.
07/2004
It was decided that low down torque needed a boost.
The cylinder and head were pulled, and planed a
few decimals of a mm on the mating faces. The cylinder
base gasket actually needed slight packing as there
was just the tiniest amount of piston contact on
cylinder head, threatening an early end to the bearings.
Raising the barrel can give higher RPM performance,
at the cost of torque as the power stroke length
is reduced. However the raised compression allowed
the torque to increase although the potential RPM
ceiling will have diminished a little.
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10/2004 - New top speed = 70km/h
Time for modification to the exhaust. Two
strokes can gain a lot of power by replacing the exhaust
with a well designed expansion chamber. The replacement
chosen was a handmade KN Kikaku chamber.
The new exhaust provides a lot more power, and at
higher RPM. The factory AF28 ZX CDI is limited so
no increase in top speed here. |
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11/2004
The clutch arm springs were replaced with
stiffer items, raising the engage point higher. This
allows the engine RPM to lift higher before the transmission
is engaged. |
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03/2005
As engine power has been bumped up and we are looking
for durability, the crank was replaced with an aftermarket
item. This crank is 50grams lighter than standard,
and has a longer pulley collar for extended movement,
meaning higher possible top speed. Also the oil gallery
to the conrod is enlarged. |
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04/2005
Now that the engine's bottom end can handle
it, its time for more serious modification. Our 75cc
big bore kit was chosen. This has a ported piston,
larger port cylinder and redesigned alloy head. After
the kit was bolted up we retuned the carburettor with
bigger jets and adjusted the needle clip. A pod power
filter was added to aid breathing. The front wheel
is now difficult to keep on the ground when opening
the throttle. |
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05/2005
A full racing manifold and racing carburettor
is lined up for fitment to the Dio. The manifold incorporates
a 30mm internal diameter and double racing reed valves
with optional fibreglass or metal blades. The flow area through the petals is 3 times more than standard. The carburetor chosen
is one of our special PWK 28mm chrome flat slide carbs.
This has a manual choke, bottom plug for quick jet
swaps and the oil feed after the slide for constant
oil supply even when the throttle is closed. The difference
in engine response and high speed performance is incredible.
Once the engine is fully run in the throttle cable
travel will be extended to allow full bore use. |
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09/2005 - New top speed
= 90km/h
The engine has been fairly well run in so its time
for a racing CDI replacement. The unit chosen is easily fitted
and removes the factory RPM limit. |
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09/2005
The body is given some attention with a new eye-frying
yellow paint job. |
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02/2006
In order to improve looks and get that important air
drag down, the scooter is lowered 4cm by swapping
the front forks and replacing the rear suspension with a spring damper unit. |
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03/2006
Components are sourced for a custom wet nitrous
kit for the Dio. A stainless steel button activates
a relay which powers the solenoid valve. Carb jets
are used in the brass hose fittings to regulate
the Nitrous Oxide and extra fuel flow. This set
up will be finalised and tested once we find the
right bottle to use. |
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08/2006
After blowing a hole in the top of the piston in a high speed run we decided to lower compression a little. The modified standard head was swapped for one of our alloy high fin heads, which has optimum squish area for wide usable power and torque range plus bowl combuston chamber. The cylinder was rehoned and the main bearings and seals replaced again. New #9 NGK plug fitted. Running in is begun using mineral oil for proper bedding in. |
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| While the engine is apart we have decided to replace other parts. We now remove the oil pump and plug the hole with a specially designed sealed alloy plug to maintain the primary (crankcase) pressure. |
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| The clutch centre spring is replaced with one of our 10% stiffer springs. A new Kevlar oversized belt is fitted and the interior of the crankcase ground slightly to avoid rubbing the belt at idle. The centre spring helps to stop bogging with the increased torque from the engine, and improves acceleration when the throttle is released and reapplied. |
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09/2006
The speedometer is replaced with a Kitaco 120km/h version. Yes we will need it. The handle bar grips are replaced with Italian Progrip items that fit the Honda and most other scooters perfectly and are very comfortable. |
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| The rear suspension is now replaced with our billet alloy version, adjustable height coilover damper unit. The improvement in the rear end is miraculous for high speed cornering and control. |
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| The tyres are replaced with Dunlop TT91 GP, semi-slick medium-soft compund. These give much improved grip in cornering and more axial stability. |
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| The exhaust currently used is our chrome variable chamber for AF18E engines, this is capable of handling the volume of gas produced by this engine and gives very good low/mid range response, without producing too much noise. A mixture of 7g and 8g rollers works best with this. For competitive track use the exhaust will be replaced with a lightweight hydroformed chamber. After 200km running-in we have switched to semi synthetic oil. |
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10/2006
New Ceat Rio tyres (Made by Pirelli) are fitted, 3.00/10 at the front and 90/90-10 at the rear. These are a relatively soft compound with good dry performance and a nice profile for the track. Once warm, they provide impressive levels of grip. |
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01/2007
Some attention is now paid to the weight of the scooter. The entire headlight, surround, dash and switch unit is removed, along with the speedometer and cable plus its drive unit from the hub. The rear spoiler and integrated stop lamp are removed. The seat is lightened, and the inner leg fairing removed. |
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| The weight balance has now shifted rearward so the battery holder is removed as well as the unused oil tank, and the battery shifted to the front. A lighter battery, CT4B-BS is used instead. |
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02/2007
Now that running in is complete, the compression is raised. After calculating for a static compression ratio of 11.5:1, the head is milled 0.5mm and refitted. |
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A cold Iridium spark plug, the Denso IWF27, is fitted along with a resistorless NGK LZFH plug cap. This modification cures an occasional misfire and gives better acceleration to the bike. If run as a 50cc, the plug used is IWF22 |
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