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

To be honest it would be better with the exup as well, that would mean either sourcing a secondhand set of downpipes from either a 2TK, 3EN1 or 3EN2 the servo and the exup cables.
The cdi has probably been changed to get around the speed restriction (around 112mph) the speedo might have had the electrics removed from the back or even have had it replaced.
These bikes dont run well without the exup rejetting will be expensive and time consuming, the end result isnt great either

With the collector assembly, it could have been easier if they just stuck open the valve, but, they welded on plates...bad piece of engineering.
IC Igniter is de-limited and derestricted, I got to run it at 170 km/h without any problems. A bit worried about the rev limiter bypass...

It is not easy to source the collector set, but a Yamaha mech said you can use a butterfly valve, like the 2006-onwards R6. Dunno much about the exact servomotor model, but if needed I would have to make my own if it is hard to source one (It is simply a DC motor and a potentiometer encoder). Things that are better left as is, eh?

There is also an FZ/FZR specialist, someone that I know, telling me to use the 1WG igniter unit if eliminating EXUP, because the advance curves are way different than the EXUP one. Needs modifications to the plugs and pinout, maybe.

I'm guessing you're not in the uk, exup serves arent rare here although maybe for 3en1 it's different.
The speed restriction is at 180 kmh usually a little higher - it's a soft limiter it cuts some sparks to two cylinders (one coil)
Yes much better to leave it alone for a road bike. I've heard the R6 exup works it's part of the exhaust can so can be fitted up fairly easily get the R6 exup cables

Yeah, I'm in the Philippines. If needed, I think I can get one through some friends back at Japan...but they can't do it now with the pandemic.

One thing that I am sure of is the speedometer sensor switch is disconnected, and the wiring is eliminated. I did not risk going about 200 km/h because the brakes are crap. (Will explain in a new thread)

It seems the servomotor system did not differ across the FZRs. I bet it is possible to use the 600 servo (plentiful than 3ENs) and, if really needed, get one from an R1 or R6 that is filed away along with the stock exhaust...

I only worked with the 750s and 1000(Non-EXUP), no doubt things are different with the 400-600s. But in all case, I am used to riding with a stupendously weak motor below 6000 rpm, so I won't really mind the tradeoff, but if I can get the EXUP back, it's a great accomplishment.

It sound like you a bit on your to do list

I bought a 3EN1 a few years ago that would not rev past 6K. I did an exup-ectomy and now she runs great. I have no idea how it is supposed to run with the exup so I have nothing to compare with. Below about 8K she runs fine but then once above 8K the power band kicks in like a 2-stroke all the way up to the redline. I suspect the exup might help with pootling around town at low rpm but I certainly don't feel the need to put it back in. Just my 2 cents FWIW.

The EXUP gives you that "powerband" pretty much all the way through the rev range. The torque in the 1000/Thunderace is unreal.