Hi guys, sorry to introduce myself with an issue. I'm Tim, 28 from Norwich UK and just bought my first CBR1000F.
Intro over now for my plea.
I found out when the logbook came that I've bought a JDM '93 (on a N reg...?) CBR SC31 and when bought I was told "has an issue above 5k, probably dirty jets". I'm not mechanically inept so thought I'll whip them out and give them a clean.
Noticed immediately that there were restrictors in the head rubbers so thought to myself "Ah, that'll probably be it" and tore them out. Bare in mind these were metal restrictors, not the rubber ones that need cutting out. After successfully removing them (one shot perfectly into the airbox so had a chance to check the filter, new btw) I pulled the carbs and got the bowls off.
Main jets removed, all looked pretty clean tbh, and I noticed that they were stamped 102 (correct size for restricted JDM version, which I found out later). Ok, must be part of the restriction so what size shoud they be? Unfortunately I only had a euro-spec manual to hand, which says the mains should be 122 so got my jet drills out and bored them out to 120 (closest size I had).
While I was there I thought I'd check the diaphragms, I know they can cause similar symptoms to mine and after removing the caps, checking them all (all good btw) I went about refitting them. Strangely the springs outright refused to stop coiling around where the diaphragm wants to extend to so trimmed them all down by about an inch.
Everything back together and went for a test ride. No different from before...
Right check the plugs then. All brand new (not even a spec of carbon on them) and while doing so plugs 2 & 4's leads pulled away from the caps. Quick trim and they're tight again.
Popped to local bike breakers and got some working coils. Below 5k is beautifully smooth but same problem above 5k...
This is starting to bug me now so just ordered some standard size mains (102 for JDM) and gonna try that and see if it fixes anything.
Other than what I've already tried, and the ICM which has a number on it that I can't find online anywhere (even tried .jp sites) anyone have any ideas as to why my bike won't rev properly above 5k? It almost feels like it's hitting a rev limiter but if I keep the throttle pinned it wil creep up the revs (shaking the **** out of me all the way, like I said it's like a rev limiter).
Also does anyone know if the ICM from other honda's the same age would work as I noticed my dads' hornet has the same ICM, albeit with a different code stamped on it, same with a few early fireblades. The code on mine is MZ2F 825W 3604 if that helps.

 

Welcome to the forum Timothy, California models also had the metal restrictors, these bikes run lean at the best of times, now that you have removed the plates you will definitely need the bigger jets, I run 145 main jets, but I have had a little work done. Make sure the little bullet caps on the spark plug tips are removed (just leave the thread showing to `screw` the cap on), leaving them on can cause the boots to jump off and cause rough running and loss of top end(as spark cannot work properly.)
I am sure there will be many more suggestions soon.

 

Problem fixed now, turns out it had a speed restrictor in the speedo cluster cutting revs at exactly 5k.
Mine had replacement uk-spec clocks fitted so the chip in question had been removed from the old clocks and tied into a (semi) waterproof bag inside the right fairing. After some digging online found out that cutting the black/brown and orange/blue wires and connecting them together fools the ecu/icm into thinking that the bike is below the restriction speed, allowing full revs without limiting.
See my other post on the issue for more details (Need help quick, is this the speedo limiter on jap import 1000f?).