Anyone know if the main jet on a Rotax has any influence on low speed rpm? If your low revs are around 6000rpm will changing the main do anything or is it more needle for lower rpm? Thanks lots
The main jet will have some minimal influence on the low speed performance. The exact effect however is determined more by driving style and throttle position than RPM. When accelerating from a low speed corner the throttle should be fed in rather than stomped wide open. This ensures the intake air velocity through the carb is sufficiently high to maintain the venturi effect and prevent bogging due to lack of fuel. The main jet should be tuned for high speed operation with the needle/air screw used to adjust low speed operation.
A Rotax engine (particularly older engines) at 6,000RPM has little power as it is below the power band. Low revs of 6,000RPM is too low and usually a result of incorrect gearing or driver slowing too much for the corner.
The following, however, impact engine power - worn engine top end, engine port timing, fuel pump diaphragm, sticky power valve, clogged fuel filters, dirty airbox foam filter, fuel overflow bottle doesn't have breather holes, battery voltage low, carby float height.
Engine power shouldn't be a problem if the engine is serviced by a reputable engine builder regularly.
Comments2
The main jet will have some minimal influence on the low speed performance. The exact effect however is determined more by driving style and throttle position than RPM. When accelerating from a low speed corner the throttle should be fed in rather than stomped wide open. This ensures the intake air velocity through the carb is sufficiently high to maintain the venturi effect and prevent bogging due to lack of fuel. The main jet should be tuned for high speed operation with the needle/air screw used to adjust low speed operation.
A Rotax engine (particularly older engines) at 6,000RPM has little power as it is below the power band. Low revs of 6,000RPM is too low and usually a result of incorrect gearing or driver slowing too much for the corner.
The following, however, impact engine power - worn engine top end, engine port timing, fuel pump diaphragm, sticky power valve, clogged fuel filters, dirty airbox foam filter, fuel overflow bottle doesn't have breather holes, battery voltage low, carby float height.
Engine power shouldn't be a problem if the engine is serviced by a reputable engine builder regularly.