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8. Setup
a) Engine fine-tuning
After the run-in phase of the engine, you can start fine-tuning to increase the performance. To that effect, optimize the mixture for idle speed and change-over at
the idle speed mix adjustment screw and the main jet needle at full throttle.
This fine-tuning is greatly simplified thanks to the carburettor made of a material combination of aluminium and plastic. Carburettors completely made of metal
get very hot during operation. This causes parts of the fuel to evaporate in the carburettor.
Consequently, the carburettor setting made when the engine was cold is inconstant during operation. The low rate of heat absorption prevents this effect.
Adjusting the main jet needle (full throttle mixture)
• Start the engine and remove the glow-plug starter.
• Let the engine warm up for approximately 1 min.
• Drive the model as usual.
• If the mixture seems to be too rich, make the mixture leaner by screwing in the main jet needle by 1/16 revolution until the setting is as desired.
• Make sure that the mixture is not too lean. A light white trail of smoke should always be visible coming out of the exhaust pipe.
For an even higher performance, you can change to a fuel with up to 30% of nitromethane. However, there is the risk that the engine will show no
satisfactory performance anymore once you go back to fuel containing less nitromethane.
If you intend to always use fuel with a high nitromethane ratio, we also recommend that you replace the used cylinder-head gasket with a thicker
one to reduce compression.
If you do not reduce compression, the engine might overheat and not run properly anymore!
Adjusting the idle speed mix adjustment screw
• Start the engine and adjust the main jet needle as described above.
• Reduce the speed until the centrifugal clutch does not engage anymore and the wheels stop turning when you take the model off the ground.
• Leave the engine running for 10 - 15 seconds at idle speed.
• While you are holding the model with your hand, operate it at full throttle once briefly.
Make sure not to touch any moving parts!
• If the engine stalls as soon as you run it at full throttle, the idle speed mixture is too lean.
• Enrich the mixture by unscrewing the screw by 1/16 rotation with the engine turned off.
• Restart the engine and repeat the procedure until speed transition from idle speed to full throttle is smooth and spontaneous. A small delay in response is
normal.
• If the engine smokes heavily during transition from idle speed to full throttle and sounds very rough, the mixture is too rich.
• Make the mixture leaner by screwing in the screw by 1/16 rotation with the engine switched off.
• Restart the engine and repeat the procedure until speed transition from idle speed to full throttle is smooth and spontaneous. A small delay in response is
normal.
• Control the model as usual in order to get a feeling for how the engine responds to load changes.
• Modify the settings until the performance meets your expectations.
Once you have done these settings, a re-adjustment of the throttle stop is necessary as well.
Adjusting the throttle stop screw (idle speed adjustment screw)
The idle speed adjustment screw regulates the idle speed via the position of the carburettor slide (throttle stop).
• The wider the carburettor barrel, the higher is the engine speed.
• Turning the adjustment screw clockwise widens the barrel.
• Turning it anti-clockwise causes the slide to move further in which narrows the opening.
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