www.zxrworld.co.uk

Right guys, i currently own a ZXR400 H2, and bought it as a bit of a restoration.
The bike runs really well but has a FLAT SPOT between 3 and 4K, but once past 4K it's fine. The other thing is, it revs right round in the lower down gears but on motorways wont pull past about 100mph. It is an import, and i'm wondering is it restricted as i've heard that these bikes should be good for about 130-140mph. I striped the bike down and cleaned Carbs out etc, even changed ( on recommendation ) the main jets, from 97.5 which I believe to be standard to 102, which helped the flat spot slightly but didn't clear it.
Any advice is more than welcome, and please excuse the ignorance or cluelessness.

How are the plugs and leads looking? You'll know if its restricted as there will be 15mm holes in the inlets after the carbs. Air filter could need cleaning/oiling.

Could be worth running a bit of redex through to cout the entire system out.

Is it an import? Could be the rev limit kicking in...

sounds like it running lean to me.

take the plastic tack cover off and put a but of gaffer tape over the air intake covering no more than 1/4.
go for a bimble, make sure the bike is nice and warm before you try a speed run.
Then cover 1/3 of the air intake and see how that works out.

if the bike runs better then get the mukka on the dyno to get it sorted.

Some zorsts cause flat spots - what system is on it ?

All Jap bikes are imports - you mean a grey import

H model was JDM so it will have speed restriction - most likely whay it runs out of steam at 180KMh (112mph)

Jet sizes sound right for oem zorst.

MM!

Mori Man wrote:All Jap bikes are imports - you mean a grey import MM!

clever sod.

Thanks for the advice people.
The can is an after market thing with no markings on it, so not sure what it is. Plugs, leads, filters are all new. The new jets i put in where from the local DYNO JET centre and he advised me that the 102 main jets should be about right, but with the flat spot getting slightly better, do you think i need to up the MJ size again, maybe 104's. Could really do with putting it on the rolling road and set it up properly, but like having a crack at things myself. So i'll keep battling on and see what happens.