Why can't I use all the revs?

[Smousley1995]

Hi, I have a 1993 Jap import Zxr 400 which is restricted to 33 bhp with the usual carb plates which I bought about a month ago. I had another 1993 Zxr 400 before this which was restricted which would do 115mph and easily use all the revs and had a surge of power when going into the powerband at about 10000rpm. Unfortunately I crashed that one and that's why I have the new one with 14000 miles on the clock.
However the new one, flat out in sixth gear will only do a little more than 80mph with the revs sitting just above 8000rpm. In lower gears it will rev to the redline but there is no powerband and is just flat from 8000 to the redline with no surge of power at all. When in fifth of sixth gear it won't rev past 8000 much at all and it's not like hitting a limiter or anything, it just struggles to find and more revs. Any ideas what's causing this?
Thanks!

[banner001]

Hi, I have a 1993 Jap import Zxr 400 which is restricted to 33 bhp with the usual carb plates which I bought about a month ago. I had another 1993 Zxr 400 before this which was restricted which would do 115mph and easily use all the revs and had a surge of power when going into the powerband at about 10000rpm. Unfortunately I crashed that one and that's why I have the new one with 14000 miles on the clock.
However the new one, flat out in sixth gear will only do a little more than 80mph with the revs sitting just above 8000rpm. In lower gears it will rev to the redline but there is no powerband and is just flat from 8000 to the redline with no surge of power at all. When in fifth of sixth gear it won't rev past 8000 much at all and it's not like hitting a limiter or anything, it just struggles to find and more revs. Any ideas what's causing this?
Thanks!

first, check the sticky topics in the restricted zxr's subforum and see if/what restrictors are fitted to your bike - as yours is a jap import its likely to have CDi and kph restrictions, these will limit you to 10k rpm or 110mph or both, so you need to look at these first, if its not a problem with the restrictions its probably fuel mix/carbs.

[Smousley1995]

I have already looked at those forums and got excited because I thought I'd found the problem it did have a restrictor in the clocks but I changed them for mph clocks of my last bike and had the black box on them but no difference . I then did the clock tab derestriction method from those forums to derestrict my kph clocks and replaced them but still no difference because that only cuts in at 11mph. Also I just balanced the carbs and tuned them with a carb tuner which made it smoother and idle better but no speed difference I do have the carbs off my last bike which I tried changing over but they started leaking when I started it up so I need new float bowl seals for them. Any more ideas?

[banner001]

what CDi do you have? It will have a bold letter on the front of it, and it will be in a certain colour i.e. A in red, M in blue...

[Smousley1995]

I've got a yellow one in at the moment which I think is L and a blue one at home which I can't remember the letter. I've tried swapping them because I know the blue one worked in the last bike but neither made a difference. The restrictor from Japan will only effect it above 110mph though, I took the tab out of the clocks just in case but from actually seeing it with the clock open I know for sure it won't affect it. And it's not that the clocks aren't connected because it revs past 10000 in lower gears :/ I'm stumped as to what it is though?

[cargo]

the symptoms you describe in your first post do NOT describe a Jap model restriction

I'd guess you have some other kind of problem with carb set up perhaps...............also you say you fitted your restrictor washers yourself.................have you double checked you work?.................could you have made an error ?

[banner001]

when you get into 5th gear and it only gets to 80mph open the choke a little, then all the way and report back what happens - your bike will do one of 3 things:-
1. bog down really bad/possibly cut out, in this case you are probably too rich on fuelling at the moment, use smaller main jets, lean out the pilot, remove shims (if fitted) from needles etc...
2. pick up revs, ok so you are too lean, put in bigger main jets, increase fuelling through midrange with shims etc...
or 3. nothing - might not be carbs, back to diagnosing what is definitely NOT causing the problem.

[Smousley1995]

I used hylomar aero grade sealant around the washers when I put them in and then sprayed wd40 around them and the rubbers to check they were sealed. I've also tried it again recently and there's still no air leak so I know it's not the washers but thanks for your answer

Banner001- ill try that in about an hour when I'm riding home and let you know what happens thanks.

[banner001]

one thing, if the bike starts to bod turn the choke off immediately - you dont want to flood your engine

[Smousley1995]

Hey I just got home and tried it twice on the way back and both times absolutely nothing happened, not even a tiny change.
Just something that crossed my mind, could it be that for some reason I'm not getting a strong enough vacuum to lift up the slide and needle in the carbs?
Another thing that I should have mentioned is when rolling on the throttle, it reaches a point where rolling on more makes no difference and in sixth gear 80mph I have the first half the throttle roll on which does accelerate and the last half makes no difference at all.
Hope that might help

[banner001]

you could remove the tank+airbox and see what the sliders are doing, you might also wanna check for damage/obstructions in and around the throttle cables - something might be preventing it from turning the butterfly.

[Smousley1995]

Do the slides move up while stationary or do you have to be moving? All I know is they work on a vacuum which pulls them up the stronger the vacuum gets
Ill check after work if they do and also check the butterfly's are opening. I know the throttle cables are fine and they do turn the part that they attach to on the carbs all the way so I can't see them not opening fully but I will still check when I get back too.
I know I'm getting enough fuel as I've changed the filter and pump to the ones of my last bike to rule them out and the air filter is fine so if its not the carbs then the only other thing I can think of is a problem in the engine

[banner001]

as the piston moves downwards you create a vacuum, the more revolutions, the longer the vacuum remains and the stronger it therefore becomes, therefore the slide gets dragged backwards more, it should move whilst stationary just fine (although you might get small amounts of petrol being blown back up into the carb body (you will see a mist coming vertical from the carb).

one thing to try is the obvious - remove the restrictors and see if that clears the problem up - then you know its a fuel thing, if the problem remains, then your problem lies elsewhere.

[Smousley1995]

Aah I see well ill strip it down to the carbs after work and see if the slides are moving and if that's all fine then Ill try taking out the restrictors although my dad rode it back when I bought it and he said there was a huge flat spot at 8000 so I don't think it's the restrictors.

I still have the carbs off my old bike but when I fitted them to the new one and started it there was fuel leaking out of them but I might try fix them with seals/bits from the working carbs because then I can completely rule out the carbs

[ross46]

I know this has moved now to more fuelling but my problems fir with the beggining, my rev counter used to go all the way up to 14500 revs, now it will only go up to 12,000 revs and then hits the rev limiter? What could cause this, ive checked all the wiring, the black wire leaves the coil up to the clocks, could it be that there's a problem with the coil itself? Thanks