TECHNICAL TRAINING COURSE

New Models: RS250

USNP9901

RS250 CHALLENGE

This is didactic material of USNP9901 APRILIA technical training course This material may be changed without any notice and following the technical development of the product

Aprilia USA USNP ver 2

The Aprilia RS250 engine is derived from the Suzuki RGV250 engine. The differences are in the cylinder, piston and head, which were designed by the Aprilia Racing department and manufactured by Suzuki. The engine is a 90 degree 2-stroke V twin inclined 20 degrees forwards in order to achieve the best possible center of gravity. Cylinders are aluminum and treated with Nickesil
Carburetor The slingshot carburetor has a slider shaped to prevent distortion and permit a large volume aspiration. The slider is made of plastic which weighs half that of an equivalent aluminum slider. Air flow through the pilot and main circuits is controlled by three solenoids which are activated according to engine speed and throttle position. This ensures good acceleration at all engine speeds. Exhaust Automatic 3 stage control of the exhaust valve port gives maximum power over a wide rev band.
Radial Flow Radiator Forward curved U shaped radiator more efficiently captures the air flow and thanks to the pressure drop created behind the radiator itself sucks air through the radiator more efficiently.
Transmission Cassette type 6 speed constant mesh gearing which can be removed from the engine whilst the engine is still in the frame.

RS250 Challenger USA

60 CV SAE 50

CV corr. SAE

8500 RPM 11500 12500

IGNITION TIMING

CRANKSHAFT
CARBURETOR AIR CONTROL SYSTEM
The carburetor uses a flat slide type throttle valve which helps make main bore air flow immediate and provide better fuel atomisation, ensuring quicker engine response. The carburetor has an air control system which supplies electronically controlled auxiliary air through the pilot air and main air passages. This control is performed by the control unit which receives the throttle sensor and engine revolution input signals. And after processing these signals, the unit outputs an ON/OFF signal to supply the engine with the optimum amount of air through the main air and pilot air solenoids.
15 Stator coil Magnet rotor Control unit Throttle cable splitting box Throttle sensor Air suction cleaner Main air solenoid RH Carburetor Leading into main air passage Leading into pilot air passage Pilot air solenoid Air suction cleaner Main air solenoid LH carburetor Pick up coil

USNP9901 MAIN AIR FLOW

PILOT AIR FLOW
FUEL FUEL FUEL/AIR AIR FUEL/AIR AIR
SOLENOID (PILOT AIR SYSTEM)

MAIN AIR SYSTEM

The normal functioning of the solenoids in relation to the opening angle of the throttle is as follows:
CARBURETOR COMPONENT PARTS
21 Top cap Cable adjuster Spring Jet needle Piston valve Pilot jet PJ Main air jet MAJ Pilot air jet PAJ Filter Throttle stop screw Starter plunger Needle jet NJ Needle valve Float Main jet MJ Power jet PWJ Chamber Drain screw Nipple Nipple Power jet II

CARBURETION BY JETS

% THROTTLE OPENING This diagram indicates where each jet affects the carburetion throughout the throttle range. PJ (Pilot Jet): With 15 % of throttle opening, carburetion is affected in the entire revolution range and with 25% of throttle opening, in the range over 9000 rpm. PAJ (Pilot Air Jet): With less than 50% of throttle opening, carburetion is affected in entire revolution range. NJ (Needle Jet): With 15 - 25% of throttle opening, carburetion is affected in entire revolution range; with 35 - 50% of throttle opening, over 9000 rpm; and with 75% of opening, over 11000 rpm. MJ (Main Jet): With 75% of throttle opening, carburetion is affected in the revolution range over 9000 rpm and with 100% of throttle opening, in the range over 7000 rpm. MAJ (Main Air Jet): From 15% of throttle opening, carburetion begins to be gradually affected, and with more than 50% of opening, it is affected in entire revolution range. MASJ (Main Air Solenoid Jet): With approximately the same throttle opening range as MAJ, it can affect carburetion. However, due to the duty solenoid control, carburetion influence is limited to within 5000 - 9000 rpm and over 11000 rpm. Note. This is absent from the RS250 Challenge. PWJ (Power Jet): With 75% of throttle opening, carburetion is affected in the revolution range over 10000 rpm, and with 100% of throttle opening, in the range over 8000 rpm.

% THROTTLE OPENING

Basically it is not necessary to change PAJ, MAJ or MASJ for tuning carburetion. Instead, replace PJ, NJ or MJ for different carburetion. Only when time is limited and changing carburetion in the pilot or main system is desired, PAJ or MASJ may be replaced as an alternative tuning. However, such a tuning method is not recommended because at times, loss of total carburetor balance may result.

EXHAUST VALVE

SPRING STOPPER No. 2 VALVE

No. 1 VALVE

VALVE GUIDE

LOW SPEED 0 - 8000 rpm

MEDIUM SPEED 8000 - 10000 rpm

HIGH SPEED 10000 + rpm

EXHAUST VALVE OPENING
On first reaching 2000 rpm, valve cleaning takes place. Change to next stage is at 8000 rpm. Final stage is at 10000 rpm

RS250 CHALLENGE USA

The vehicle is supplied with alternative front and rear sprockets. It is therefore opportune to review the correct installation procedure for circlips as shown.
Furthermore, particular attention should be paid to the correct positioning of the rear brake hanger after tyre changes and the torque required for the front axle clamp screws (10 Nm)

TOO LEAN, TOO LONG

CLEAR SIGNS OF PISTON DETERIATION DUE TO OVER HEATING
CUSTOMER HAD REMOVED THE SUPPORT RING UNDER THE LOWER PISTON RING, CAUSING A LOSS IN CENTRALIZATION (VERY IMPORTANT DUE TO LARGE PISTON/CYLINDER CLEARANCE)