zxr400 queries

[Milky]

As some of you may be aware, I just bought a 91 zxr400... I will post some thing like a picture when i get around to it/get a digital camera for those who are interested :)
It has an old Kerker off a 900 on it, as the standard/previous can was rusted out. As a result, the jetting is not quite right - a little flat spot around 6-8g, which is accentuated by running it on 91 octane petrol. Can I have some advice on what I think are my only options:
1. get a standard can for it - Unfortunately from what i have seen all these are bolt-on which might not be compatible with the current slip-on can. Maybe another can from a similar 400 will work?
2. get the jetting redone for me - AFAIK this cost heaps, which doesnt fit with my finances :(
3. Do the jetting myself by buying a kit of needles for the carbs - I am capable of removing them and doing the work myself, but when it comes to engine remapping, I have absolutely no idea... Is this even necessary for the bike to run smoothly?

Thanks heaps guys/gals

[Milky]

Ooo i forgot... Do you think that I might do some damage to the exhaust valves by continuing to run it with the less restrictive exhaust? I seem to remember there needs to be a certain amount of backpressure for the valves to cool effectively... something like that anyway :wacko:

[Hoon]

Is the flat spot at part throttle or full throttle or both?

First thing I would do is strip the carbs and check them out to make sure they are all working properly.
The ZXR400 carbs don't have adjustable needles but you can just use washers instead - just to see if it makes a difference. Saves you buying needles which mightn't even fix the problem.

[phil_elvey]

Yeah hard to say without more info, but using washers to raise the needles (richen the mixture) could well sort the problem

[Motu]

Was that you on the green watzit I saw go past today following that ugly BMW?

[FROSTY]

motu--Id say that was a definite yes- :killingme

[Posh Tourer :P]

Thanks motu.... :P Must drop in sometime and say hi....

[Milky]

Is the flat spot at part throttle or full throttle or both?

First thing I would do is strip the carbs and check them out to make sure they are all working properly.
The ZXR400 carbs don't have adjustable needles but you can just use washers instead - just to see if it makes a difference. Saves you buying needles which mightn't even fix the problem.
Hmmm... havent noticed too much difference in the flat spot with throttle position, but then again I havent taken much notice... I took the airbox/tank etc off to check the carbs were pulling up evenly, but didnt take them off as far as floatbowls etc... maybe that is a job for a day after exams when it is raining ;) For placing washers in there, will any sort do? or is it important to keep them the same material as the needles/carb casing? I am thinking about petrol and reactions with metals - dont want the washers to fuse on there after a few months because of some deposits...

I will go for another ride sometime and check that flatspot under half/full throttle :ride:

[Milky]

Yes motu, 'twas I... I was heading into Uni via scenic drive and glen eden ;) seemed a pretty direct route to me

[Milky]

bump....

I checked the flatspot with a full tank of 96 in it and it is greatly reduced :) However it still pulls a little unevenly through the rev range - a lull from 5,5 to 7,5 i guess is the best way to describe it. From what I could tell, the flatspot isn't always there - it varies in severity depending on throttle opening. low/half throttle seems worst, under full throttle it doesnt appear so much. It does seem to run a bit better on just a little bit of choke - when it is hot it doesnt get swamped until 3/4 or full choke at idle. I guess that means it could be a bit richer then...

[FROSTY]

If ita any help mine is flat as a pancake till it hits 7k then it starts to make propper power