To Exup or Not to Exup
Posted: Wed Jul 15, 2020 2:04 pm
I want your opinions!
We all know that Yamaha developed the EXUP system to compensate for the power pitfall at lower engine speeds due to the engine's higher state of tune, thus maintaining the high RPM hit while providing increased flexibility through a wider usable powerband (which also helps back then due to horrid shifting action...).
My bike is a 1988 FZR400 3EN1, which the EXUP valve was eliminated by the first (after the Japanese) owner because the engine won't rev above some 7000 rpm or so, and also eliminated the servo.
I do know that if you take the servo off the igniter will go into some sort of limp mode, but this bike's igniter has been cracked open, the rev limiter eliminated.
The engine requires a top end overhaul sometime to check valve stem seals (I see some intake valves looking moist at the stems...) for the smoke issue I have on cylinder #3 (#3 from the stator side)
Reason why I am asking this is because of jetting issues, getting a 'womp-womp-womp' sound at around 3000-4000 rpm which mean something's up with the pilots and synchronization, and I just cannot go out and test adjustments due to lockdown policies.
Or should I just source the servomotor, and jet it correctly as soon as possible without EXUP???
Thanks for any response
We all know that Yamaha developed the EXUP system to compensate for the power pitfall at lower engine speeds due to the engine's higher state of tune, thus maintaining the high RPM hit while providing increased flexibility through a wider usable powerband (which also helps back then due to horrid shifting action...).
My bike is a 1988 FZR400 3EN1, which the EXUP valve was eliminated by the first (after the Japanese) owner because the engine won't rev above some 7000 rpm or so, and also eliminated the servo.
I do know that if you take the servo off the igniter will go into some sort of limp mode, but this bike's igniter has been cracked open, the rev limiter eliminated.
The engine requires a top end overhaul sometime to check valve stem seals (I see some intake valves looking moist at the stems...) for the smoke issue I have on cylinder #3 (#3 from the stator side)
Reason why I am asking this is because of jetting issues, getting a 'womp-womp-womp' sound at around 3000-4000 rpm which mean something's up with the pilots and synchronization, and I just cannot go out and test adjustments due to lockdown policies.
Or should I just source the servomotor, and jet it correctly as soon as possible without EXUP???
Thanks for any response