Kawasaki ZXR400 Derestriction issue

[joezxr]

hello, i own a 1992 zxr 400L model and im having a few problems with the top speed brick walling at 110mph

iv looked around lots of forums and i know about all the restrictions but my problem doesnt really match any of the restrictions that i have been told it could be.

basically my bike revs to 14k in every gear and absolutely flies to 110mph but then stops and is trying to pull further buy really struggles as if its being held back, i have a yoshimura exhaust silencer with the normal manifold but with no restriction plates on the manifold, i have english mph clocks and an UK blue sticker "M" CDI.

i have replaced and maintained everything on my bike that could be effecting this problem but i cannot figure out what is wrong, i have changed all the spark plugs, checked all the HT leads, cleaned my carbs, sealed my airbox and inlet rubbers, replaced all of my fuel lines and made sure they are all clear and my carbs are set to 2 1/4 turns out each, i balanced them the other day and my airbox snorkel/hole bit currently is half taped over to balance out the mixture of air and fuel.

like i said this current set up runs great, the whole rev range is smooth as anything and the plugs are a lovley coffee brown colour! the confusing part is i have had 130mph out of the bike previoulsy with the same engine but im beggining to believe the clocks were lying and i was just sat at 110mph the whole time! the previous owner of the bike who is a friend of mine also said he had around 140mph out of the SP engine he used to have in the bike but also came across this problem eventually and cant remember how he fixed it.

i would just like some advice on what it could possibly be? i have no more ideas... does anybody know 100% all of the restrictions on a zxr 400, iv heard about some resistor to a pink wire on the ecu or some crap but i have no idea...

[CaNsA]

Posted here?

https://www.zxrworld.co.uk/zxr400oc/viewforum.php?f=164

[joezxr]

[Bikeless]

If its a grey import like the CBR I had,it may be restricted through the clocks,on mine there was a sensor in the clocks and when a vane on the back of the needle passed through the sensor it cut the ignition. Removing the vane derestricted it but if you removed the sensor or wiring it would still be restricted,maybe when yours had the UK clocks fitted,they were not wired correctly leaving the CDI in restricted mode.

[Bikeless]

According to 125ccsportsbike forum,you sorted it last August and had 135mph??????

[joezxr]

[Bikeless]

TBH,your not going to see much more than 130 mph on the speedo with 60 bhp,sounds like it is fine,if it was still restricted,it would not go past 112 mph on the clocks.
My Blade would show 175mph on the clocks but realistically doing 155-160 mph and that had 120 bhp. With 60 bhp you won't get a true 130 mph IMO.

[Frost]

Sounds far too close to the jap 180kph restriction speed to be a coincidence.

[joezxr]

well then i guess its restricted.. problem is i have the derestriced uk CDI so it doesnt make sense...

[Wafer_Thin_Ham]

Is it a UK bike, or a parallel import from Japan?

The CDI wouldn't know which gear you're in I wouldn't have thought, so it wouldn't be restricted through that? Usually they're restricted via the clocks, so you fit an MPH converter to your KPH clocks, to get around it.

Why not unplug the speedo drive and go for a run? At least you'll know if it's the clocks causing the issue.

Do a GPS run before and after.
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[joezxr]

[Bikeless]

[Wafer_Thin_Ham]

[Bikeless]

Good point,I'm still not sure if they would be mechanically driven or electronic???? Other forums say you need an electrical box which would point at them being electronic.I would do more research rather than risking thrashing the bike trying to do GPS measurements at that speed.

[joezxr]

right i just got back in from doing 2 tests with the speedo unplugged

this time i managed to get 112mph and 114mph but ran out of "private" road, still felt like there was more to pull though

so whats the verdict now?

the thing is that other forums mentions using resister boxes to trick your cdi, the speedo is mechanical but is also connected to the the CDI through a pink wire, but i dont have a pink wire, it must have been replaced with a different color which i dont know lol also dont forget theres two models L and H and the H models need a lot more done to be derestricted apparently, my model is L

[Wafer_Thin_Ham]

[Kickstart]

Hi

I would suggest getting the bike dynoed. Find out how much power it has and whether it is well down on power. 110mph or so is only going to need ~35hp at the back wheel. Could also be interesting to do a power run in a lower gear and also in top gear (see if the power graph is cropped off at the top end in top gear).

All the best

Keith
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[joezxr]

[Bikeless]

If it coughs and farts and feels like its firing on 2 cylinders when you hit 112 then its still restricted,has it definitely got a UK spec CDI?

[joezxr]

[joezxr]

[Wafer_Thin_Ham]

[Kickstart]

Hi

Not really suggesting a setup session, just a brief run or 2 after lobbing it on the dyno.

Could be many things but I do tend to agree with Frost that the max speed you are getting is too close to 180kmh (ie, Japanese market restriction) for comfort. But it also needs so much less power than standard that it should be very obvious on a dyno.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[joezxr]

yeah i read up somewhere about having to solder a resistor inline on some wires but apparently that is on older H models, and mines not that so im just left where i was in the first place!

i could try a dyno i guess but id much rather just fix the problem rather than just being proved it is restricted if you get what i mean haha

EDIT: problem fixed, it was basically after around 100mph the amount of air being taken in was to much and making it lean, iv taped up the airbox a bit more and had a few tests runs and it pulls past now