2006> RS50/RX50/SX50 De-restriction, Reliability & Performance Upgrades - Aprilia Forum: Aprilia Motorcycle Forums
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post #1 of 11 (permalink) Old 11-08-2016, 07:31 AM Thread Starter
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Thumbs up 2006> RS50/RX50/SX50 De-restriction, Reliability & Performance Upgrades

For all bikes using Derbi Euro 3 D50B0 & D50B1 engines:

Carburation and fuel tap

I don't recommend trying to re-jet the stock Dell'Orto PHVA 17.5 carburetor. Dell'Orto's are designed to be the worlds most tunable carburetors with the aim to "extract maximum performance" and offer "enhanced crisp throttle response" rather than provide safe balanced A/F (air/fuel) mixture ratios across all throttle slide positions. They are a pain to setup w/o destroying multiple engines in the process, and very sensitive to altitude air density changes in ever-changing warm / cold climates. Dell'Orto jets, Atomiser emulsion tubes, needle tapers and throttle slides cost a damn fortune.

The Polini CP 17.5 carb uses 1 simple throttle slide, 1 simple needle and 1 simple Atomiser which don't need swapping for different sizes in order to jet the carb sufficiently for the utmost safe running.

To mount and jet this carb correctly you will need the following parts:
Polini 34mm Airbox boot adapter, part number: Polini 343.0023
Polini CP 17.5 carburetor, part number: Polini 201.1700
Or if you want to continue using the handlebar cable choke' part number: Polini 201.1702 (comes with 34mm adapter)
5 pack of 42 - 52 pilot jets, part number: Polini 372.0004
10 pack of 80 - 98 main jets, part number: Polini 370.0002
2mm silicone blanking cap for cylinder head carb heater port.
4mm cap for the plastic T-piece near coolant overflow bottle (see MVT ignition photo)

Not 100% necessary' but i recommend fitting the CP "Evolution" float bowl for quick and easy main jet access, part number: (Polini 343.0009) rather a shame they chose not to include this with the standard version tbh.

Cut the 2 pieces with green arrows pointing directly to them from the intake manifold so the Polini carb body sits flush with the manifold properly.



Insert the included blanking caps on the carb "fuel cock depression" and "mixer" vacuum ports, the "mixer" is made redundant when switching to premixed fuel, and the other is made redundant when the auto vacuum fuel tap is disconnected. These auto vacuum operated taps are immensely unreliable, diaphragm broke on 3 of them. Fuel flow rate goes on/off while the engine is running - creating a dangerous lean running condition.

Therefore' an old design rugged manual operation non vacuum tap is needed. Tried 3 styles of 15mm manual taps, the only one that doesn't leak while turned to the "OFF" position is the OEM Derbi Senda 125/Cross City 125 tap, part number: Derbi 00H00404181
When purchasing this tap' make sure it comes with the black dial, some places don't even include it.


Tip: Free Line Kart fuel line is manufactured from Tygon, molds over connections and doesn't require retaining clips. Tygon doesn't go rock hard and split like old tech rubber / silicone does.

Quote:
Solution, trim the pipe down by 15mm. By doing this you still have a safety net as these Derbi models do not have fuel amount gauges, so you still maintain a reserve tank. But your allowing fuel to get into the green pipe and thus into the carburettor.
This feature is a reliable way of knowing when you need to refill the fuel tank.. unlike the digital instrument's low fuel warning light that often fails to flash due to the inferior quality Spanish / Italian wiring harness which usually shuts down the whole instrument dashboard. Once the engine starts cutting out' pull in the clutch lever - reach down and switch to "RESERVE" while keeping eyes on the road ahead.

If the engine cuts out straight away' pull in clutch lever and coast to a stop. Never change down gears while coasting with the engine switched off, this won't do the transmission any favours. Always turn to "OFF" position while the engine is switch off, unless priming a cold engine before firing it up.

Last edited by MacGuyver; Yesterday at 08:49 AM.
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post #2 of 11 (permalink) Old 11-08-2016, 07:32 AM Thread Starter
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Exhaust


If you grind out the manifold washer and saw the resonator pipe off the OEM exhaust, you will still have to saw the expansion chamber in half to remove the catalytic converter, which not only restricts power.. but also creates huge amounts of unnecessary extra exhaust and engine heat. After i removed the catalytic converter baffle the performance difference was barely noticeable compared to an aftermarket exhaust.

For the sport bike frames' use a Giannelli/Arrow exhaust
For motard/enduro frames' use a Yasuni Cross ML exhaust



Giannelli/Arrow come with 1 restrictor washer in the front manifold, Yasuni's come with another in the muffler. Here's how to remove those restrictions http://www.pedparts.co.uk/blog/yasun...-to-derestrict
Remove factory lacquer finish from the exhaust with steel wool or methylated spirits and paint with a few coats of any good quality tinned brush-on VHT paint as an effective rust deterrent.

Disconnect 2 cycle oil injection


The injection pump churns out 2% (50:1) ratio @maximum pump cam opening. With the pump cable adjusted to its limit, cam only opens to around 75% of its full rotation at full throttle slide opening. So less than 2% oil mix unless you physically hold the cam fully open. Premixing 3% (32:1) is much healthier for engine service life and reliability.



Drain off radiator coolant and transmission oil' remove the clutch cover and remove the 2 plastic pump drive gears from their shafts. Unbolt the oil pump and remove the pump drive shaft. Then remove the pump cable from throttle cable Y splitter and remove the oil tank from the frame. Reinstall the pump or use a blanking plate like this..


Stiffer clutch springs

Due to enhanced performance gained from the aftermarket performance exhaust' the clutch friction plates may begin to slip under hard acceleration - especially on cold engine before warmed up, many owners install shim washers to counteract this w/o realizing the total pressure plate distance travel will be less and clutch dragging usually occurs. The stiffest quality springs on the market are Malossi MHR's which are used in GP 80 cup bike engines, part number: Malossi 2912018

The clutch pull will now be immensely heavy with Malossi MHR clutch pressure plate springs, saw LH switchgear OEM lever mount down and fit an easy pull clutch perch/lever, highly recommend the Pro Taper Profile setup: Pro Taper 024101


Last edited by MacGuyver; 02-23-2017 at 07:31 AM.
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post #3 of 11 (permalink) Old 11-08-2016, 07:32 AM Thread Starter
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Gear selection restriction


In some countries' these engines are limited to an even dangerously slower 30.58 kph (19 mph), this is done by restricting owners shifting higher than 3rd gear by means of a different shift cam plate. The correct cam plate for reaching 4th 5th and 6th gear is part number: (Aprilia 847038) you'll also need to swap the 11T front sprocket for a 14T sprocket part number: JTF1128.14

Refill the transmission with 650cc mineral-based JASO MA2 API SJ specification 10W/40 4 stroke engine oil, fill coolant/antifreeze no higher than the overflow bottle maximum mark. If fitting brand new clutch plates don't forget to pre-soak them in fresh oil before installation. Always use OEM Derbi/Aprilia clutch friction and steel backing plates for the most durable service life.

Polini CP jetting and Premixing


Drain off all fuel from the tank.
Get a useful oil measuring bottle, part number: Polini 121.500
Fill to 5 liter mark on the 3% scale with cheap 2 cycle mineral-based oil that meets API TC or JASO FB specifications, add this to 5 liters of fuel. Shake the Jerry can vigorously and then pour the premixed fuel into the tank. When filling up at fuel stations' always pour oil into the tank first and add fuel at the quickest rate the nozzle allows w/o creating a "fountain" effect, squeeze the front brake lever and pump the forks a good few times before re-starting the engine.



Take out the carb throttle slide needle and put the clip on 4th notch down.
Remove the float bowl and change the pilot jet for size (49)
Change the main jet for size (92)
Turn the air screw clockwise until fully seated, then turn anticlockwise by 1 full turn (from 12 o'clock to 6 o'clock = half a turn).
Adjust the throttle stop screw to reach the desired idle rpm speed after starting the engine.

WARNING!
DO NOT rely on spark plug insulator color or piston wash deposits for providing correct safe air/fuel ratio indications. Those old methods are highly inaccurate and frequently used / recommended by gullible, incompetent fools who cannot accept the fact: only D slide and flat slide carburetor designs offer "maximum fueling performance".

Go for a ride' warm up the engine before completing a few high speed full throttle runs, during this you will notice the engine begin to sputter before reaching the rev limiter. While this happens the engine is effectively firing on every 4th cycle "4 stroking". Reduce the main jet size by 2 numbers each time until this 4 stroking stops.

The bike may still lose forward momentum when rolling from half - full throttle, except the 4 stroking @full throttle has now disappeared. It may speed up when rolling back to half throttle. Reduce main jet size again by 2 numbers each time until the bike maintains forward momentum w/o slowing down @full throttle. You'll notice the "4 stroking" appears @1/4 throttle. If it 4 strokes massively, lift the clip no higher than 2nd notch. At this point the carburetor is perfectly jetted for cooling the piston, cylinder, bearings.

If you live in high altitude areas where air is naturally less dense, you might find an 80 main jet is too rich for the Yasuni ML pipe. If so' try the 60 - 78 pack: Polini 370.0001

2 strokes were designed to burn dirty, emit blue clouds of smoke and sputter through 1st / 2nd gear after idling for more than 3 seconds - especially while running healthy premix ratios. The main reason mx and road racing involves whacking open the throttle many times on starting grids before the gate drops or amber light turns green.

Replace the OEM ignition

The Ducati ignition only lasts a little while before the stator winding gives up it's ghost, cheap China and Tiwan stators are even worse. When the stator fails don't go replacing the CDI module, as this never really fails. Replace the whole ignition with the french made MVT Millenium EXT 111 kit.


...but don't ground the Blue 45 km/h restriction wire...


Last edited by MacGuyver; 02-23-2017 at 04:47 AM.
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post #4 of 11 (permalink) Old 11-08-2016, 07:33 AM Thread Starter
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Larger capacity cylinder

I recommend Airsal's Nikasil plated aluminium 80 sport kit with dual ring piston..


When installing a new cylinder kit' insert piston rings with ring letter or number facing upwards, make sure piston crown arrow faces the exhaust port. Insert 1 gudgeon pin retaining clip before sliding the pin through' cover the exposed crank area with a rag to prevent dropped pin clips or debris entering the bottom end. Give the crank rod big end bearing, small end bearing, gudgeon pin, piston and cylinder walls a nice coating of 2 stroke oil. And apply fuel/oil resistant sealing compound to all paper gaskets. Never use a stanley knife blade or anything metal for scraping off gasket material, only plastic scrapers should be used since plastic is softer than aluminium.

If you want to stay with the OEM 49cc kit' remove the cylinder head thermostat and replace the head gasket and O-ring...


Cold starting procedure:

When a bike hasn't been ridden for a few hrs, or parked overnight etc.. always "prime the engine". Some of the fuel/oil mix protective coating on the piston and cylinder will begin to slide off after a few hrs due to gravity's effect. With the ignition switched off' prime the engine by pressing the kick start lever to the bottom of it's stroke a few times in order to allow lubricating fuel/oil into the cylinder before switching ignition on and starting it up. On RS/GPR models with starter motors: select 2nd gear while pushing it down the garden path or out of the garage and release the clutch lever to the biting point a few times.

If it requires using the choke function' press the choke knob back down ASAP when if fires up, modern chokes draw more fuel into the cylinder which results in a 2 stroke entering the exhaust's power band, pistons expand faster than cold cylinders.

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post #5 of 11 (permalink) Old 11-19-2016, 04:58 PM Thread Starter
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Remove the radiator un-cooling fan

The Gilera SMT and RCR don't include the typical Comex radiator cooling fan...


...someone at the Gilera end of the Piaggio factory obviously had their Italian electronics head screwed on properly. This fan adds unnecessary weight for no useful reason, even after engine seizure/boiled over coolant the fan does not activate. Unplug and remove it, this allows head winds to escape the radiator's rear grills more sufficiently allowing for better airflow.

Preventing a damaged battery

No battery box cover included with motard/enduro models...


Place a few pieces of high density foam underneath and on top of it.

Always pull the clutch lever in before decelerating

There is little to no engine braking on 2 strokes' every time you decelerate or descend down a hill with clutch drive plates engaged the engine is still creating heat while the cooling system's being fed less cooling air from headwinds. When closing the throttle grip' the carb needle taper lowers into the atomiser and reduces the maximum amount of fuel an engine can draw into the cylinder with vacuum pressure. Closing the throttle grip while decelerating with clutch lever out @high rpm is neglectful.

Last edited by MacGuyver; 01-25-2017 at 08:38 AM.
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post #6 of 11 (permalink) Old 12-13-2016, 10:41 AM Thread Starter
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Smile Internal inspections and ring changes

In the workshop manual it only specifies: complete piston replacement every 15,000; 30,000; 45,000; 60,000 KM. Piston rings are sold separate for many 2 cycle engines for a typical reason, you don't need to replace a piston every time the rings wear out. Below is a photo of the Airsal piston from the 78.5cc "sport" kit. This piston was reinstalled with new rings + small end bearing, the photo shows how a piston condition should be with minimal score marks and black spots on underside of the crown..


If using a synthetic oil then expect more ring blow-by and also if exceeding the recommended ring change intervals, telltale signs are brown or dark coloring on piston walls below the rings like this..


If jetting is too lean from typical user error, air leaks from gaskets, split intake manifold rubber, water pump, damaged radiator or thermostat failure, the crown underside dark spot will cover much more surface area and may also show a little brown.

Here's pics showing piston condition of the previously used Airsal Cast iron 70 kit..


This kit was run on the fully de-restricted OEM exhaust' which is limited to around 9,000 rpm or less. Covered at least 18,000 miles on this kit before switching to the Nikasil plated aluminium 80 kit. Aftermarket pipes rev higher, higher rpm's = accelerated wear n tear rates and higher engine temperatures. So a piston will typically show more scoring marks and worn rings after around 15,000 miles rather than 18,000 miles. Always renew the small end needle cage roller bearing, and gudgeon pin retaining clips when renewing piston rings.

If you've been jetting the carb lean, it will look similar to this..


..which will require a full engine rebuild.

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post #7 of 11 (permalink) Old 12-28-2016, 01:23 PM Thread Starter
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Exclamation Protecting the Pipes


Without some kind of stone chip shield' VHT paint gets scratched off and rust begins forming which means repainting the pipe area behind the front wheel. Install a universal 2 stroke motocross pipe shield to deter this common issue with non-japan black finished steel pipes. These universal 2 stroke aluminium pipe shields / guards can be found in most ebay stores' look for the cheapest price though, because some stores are put their own labeling on the sale listing and charging twice the price for a not so expensive item.

These shields do tend to rattle a bit at low rpm' but you can always saw it shorter since only the widest parts of the expansion on a side mount pipe would scrape off the ground in falls. The idea for best paint protection results is to bend the shield round the downpipe and situate as close as possible to the exhaust port area. For those of us who ride RS GPR sport bike models with lower fairing panels removed' install the shield like so...



Should you heat wrap an exhaust?


Using heat wrapping on exhaust pipes quietens down the tin can noise which seems a nice benefit, until a dozen cracks in the metal begin to appear. Arrow exhausts are made from very thin sheet metal... making them louder than others and are a prime example for developing cracks. Therefore' heat wrapping an exhaust pipe only makes first world problems much worse and costly in the long run.

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post #8 of 11 (permalink) Old 01-04-2017, 10:42 PM Thread Starter
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The Euro 3 D50B0/D50B1 LH engine casing has a captain obvious design flaw, no gasket used to help seal out water, dust and grime. Therefore' removing the flywheel and scrubbing round with a small brush is necessary general maintenance every 5,000 tarmac road miles, every 12 dirt road rides or every 1-3 mud trench rides.

Extraction tool size for MVT Millenium flywheel: 27 P. 1,25



Extraction tool size for OEM Ducati flywheel: M19 P. 1



Torque wrench users:

Recently stripped some crank nut threads using a Draper 3/8" drive. OEM manual torque spec 35 - 45NM. Began with a safe 25NM and it refused to click, but it was already too late...



Many experience the same issues with clickers being far out of calibration - despite following manufacturer care and storage guidelines. The more you use a "clicker" the more they seem to drift out of accuracy. Crankshafts are manufactured from steel, nuts from soft aluminium to prevent ruined shaft threads.

Only 1/2 drive beams available in the UK. So despite being cheaper than clicker designs, i paid nearly double the price due to overseas shipping from murica. And will have to repeat this when i have enough funds to replace the 1/4" drive clicker, which was responsible for stretching one of the cylinder stud bolts on the previously used Airsal iron 70 kit.



^ Arrived yesterday morning after a 2 week shipping wait, torqued the nut to 45NM faultlessly. Rather than typing an endless TL;DR, i'll post a video i found that puts things into an obvious perspective.


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post #9 of 11 (permalink) Old 02-07-2017, 11:27 AM Thread Starter
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Default Vacuum Air leak Prevention and Air Filter maintenance

If you bought one of these bikes used' chances are.. previous typical millennial teenage owner(s) may have messed around with drilling holes in the OEM airbox, or removed the airbox snorkel during the derestriction process. These air intake "improvements" are almost always a metaphor for a dog chasing its own tail, if they paid any attention to OEM exploded part diagrams.. maybe they'd realize they're actually decreasing performance with the 100% free DIY airbox modifications.


All new bikes come with a type of fuel/oil resistant sealant applied to the airbox boot pipe and snorkel. The boot pipe is prone to developing splits when the rubber goes hard after a few years. When you replace it' you will also have to reapply a sealant designed to form a proper vacuum seal between 2 joining surfaces.

As it happens.. the 2nd previous owner i bought my RX from admitted to partially derestricting it, but did not mention "experimenting" with the airbox snorkel. There was no sealant to be found on the snorkel' and dirt was clearly visibly on the joining surface = no vacuum seal = lean jetting = rpm's hanging before returning to idle.

No matter what the dishonest sales rep in a local shop might protest' RTV silicone is fuel/oil soluble and not suitable for vacuum sealing, it dissolves and will very likely be sucked into the engine. The correct sealant type is "Weatherstrip", i use 3M 08001 Super Weatherstrip and Gasket Adhesive in Yellow, this color is easily visible for seal coverage area peace of mind.


You absolutely MUST wear gloves when handling weatherstrip adhesive, weatherstrip is fast drying and sticky like super glue, solvent content is very strong, and it gets all over the place.


Air filter Oiling

Without a fine layer of oil' foam filter elements cannot do their job properly, FACT. Cleaning and re-oiling the foam element should be included with your general wrenching maintenance, there are plenty of guides on the internet on cleaning and oiling foam air filters. Just google "how to clean dirt bike air filters" and remember not to twist it like a dish cloth, because you'll only damage it.

You don't need "special" extortionately overpriced cleaning liquids / solvents, just a mild warm bucket of tap water with fairy liquid. You also don't need "special" foam filter specific oil. Before foam filter oil' there was 30W 4T engine oil. This was non-tacky stuff that got sucked into engines too easily and half of it would run down the foam element, leaving a small oil pool in the airbox. Chainsaw bar oil is tacky and very cheap to get hold of. This also serves more purposes: lubricating your bike's chain w/o flinging off too easily, lubricating frozen garage door and ignition key locks in colder months.


Spend the money you saved on not paying for the local sales rep's gold plated champagne bottle cork-cracking cruise ship holiday on refilling the fuel tank more often, and clocking up many more miles.

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post #10 of 11 (permalink) Old 02-12-2017, 08:28 PM Thread Starter
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Thumbs up RX / SX Front Suspension Fine-Tuning

The RX forks are too soft for doing their job sufficiently, always clanging into their bump stops. This results in huge front end nose diving, sacrificing rear tyre traction when it matters most and terrible front wheel deflection over rocky surfaces. Marzocchi Magnum 40 forks were employed until 2008 when Aprilia switched to Kayaba 40's.

Put the bike on a lift with front wheel off the ground, much easier to loosen the fork top caps while the tubes are still secured in the fork top plate. If you already removed them from the bike' place fork tubes in a vice using soft aluminium vice jaws with rubber grips. Undo fork tube top caps, remove preload spacers and springs, then drain old oil into a container. Fork oil must be renewed at least every 18 months.


The SX motard uses shorter springs, and longer preload spacers. Less spring coils / shorter spring = stiffer spring rate and higher sag measurement. Swap the RX springs and preload spacers for the SX parts.

2x SX springs, part number: 00H00207171
2x preload spacers, part number: 00H00203151

2008> Kayaba (KYB) Forks

2x SX springs, part number: Aprilia 864905
Both KYB's use the same preload spacer, springs will be around the same length, and heavier / stiffer Kg's rating.

Fork oil Height and Viscosity

Adding more oil reduces air volume. Air is compressible, a smaller airspace is harder to compress, which results in a stiffer fork and increased bottoming out resistance. Aprilia specifies 445 milliliters of 10W oil for each stem. Too much oil will prevent forks from compressing to the bottom of their stroke, this will very likely result in burst fork seals. 5ML higher than OEM is reasonably safe, 450ML. When adding oil' you must compress and decompress the tubes to allow some oil to purge to the bottom, which allows pouring in the correct quantity w/o overflowing all over the place.

Marzocchi springs cost a whole lot more than Kayaba's. If you cannot justify buying a new pair.. or dismantling used SX forks off ebay. Then use a thicker 15W oil instead. Thicker viscosity slows down both rebound and compression damping at the same time, resulting in an overall stiffer feel. 20W may slow the rebound damping too much, which impairs handling and ride comfort over bumpy terrain. FYI.. W = Winter, not "weight".

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