Flat below 4,000rpm

[extonyg]

hello everyone i am new to the forum, i have brought a zxr 400 L1 uk spec a couple of months ago, i love it except it seems to be very flat low down in the revs. its fine higher up the rev range but very flat below 4,000rpm when pulling away etc.
i have got an art can and non standard down pipes, with standard air box and filter with snorkel fitted still.
all four carbs have 96 jets in.the carbs are uk carbs (32mm) with heaters.
i balanced the carbs and it was a little better so i adjusted the mixtures out slightly to 3 turns out and again its a little better but still not right if i adjust them out any further it doesnt like choke at all just dies.starts fine and idles ok without choke, the idle does seem a little 'lumpy' tho a bit unsettled. so im guessing its running a bit rich now.i havent yet removed the carbs to clean them out this is my next plan.
i think im right in thinking that around 4,000rpm is where it swops from pilot jets to main jets am i right?
i was just wondering if you have any ideas why it holds back like this and what are good jet sizes to use.
thanks alot for your help

[cargo]

they dont make too much below 4K............................and I don't ride mine there.....................

[Scott221]

I find my bike is most happy 6K and above.

[extonyg]

ye i mean i dont sit below 4k but just pulling away and that just seems a little too flat to me maybe im just expecting too much from it and thats just the way it is.thanks for your help anyways

[Scott221]

I know what you mean, when pulling away. But thats just down to the bike having very little torque. It produces all its power from 10,000 to the redline. Try slipping the clutch abit more when setting off. Once you get it going, keep the engine singing and its plenty fast enough!!

[masterofinsanity]

used to keep mine in 3rd and about 8-10k revs........thats what a zxr400 is all about.

[Tyrant]

You've got to give mine some beans or it tends to bog down. The answer is to slip the clutch more or leave every junction like your Rossi.

[extonyg]

ye ok thanks for your advise ill try and get out when the weather is nice its being raining last few days round here so no fun hopefully get out at the weekend.
i would love to be half as good as rossi!!!!

[xlr8_07]

i had a similar prob, wound the low speed jets into 3/4 of a turn out and its as peppy as hell now

[extonyg]

o rite i have the carbs off at the moment to give them a clean i havent tried the screws this far in yet maybe i will. what size main jets are you using and what settings are your needles on if you have adjustable needles.thanks for your help

[extonyg]

just thought i would give you all an update and ask a few more questions
i have had the carbs out and cleaned them out so they are pristine inside, i found 2 of the locators for the diaphrams to be blocked!so i cleaned them out and put the carbs back on and gave them a go.it seems to pick up a bit better but still not 100% i have a little bit of a 'splutter' about 4k but better then what it was.i also found my air box to be 'warped' and not sitting flush onto the top of the carbs so i got some sticky foam strips and stuck them to the bottem of the air box and bolted it back on to form a sort of gasket to take up the gaps were the airbox was warped. what a difference that made its so much better still not 100% yet but im getting there as the revs still tend to hang on a little.which i think is down to the carb rubbers leaking (i have some on order just waiting for them to turn up).
i also noticed that the 2 bolts that go through the airbox holding it on through big holes in the air box are these suposed to be open or covered up??because surely this is just like a big airleak as it is after the filter.well i blocked them up with rubber grommets anyways and the revs dont seem to hang as long anymore or maybe its just me thinking it.
does anyone no if there is supposed to be something covering these or not?
thanks for your help

[RedexRobB]

There are supposed to be rubber bungs that go in place to block them up. Some electrical tape would probably do the same job. But sounds like youve just had one big air leak. Ive heard of the trumpets warping due to heat but never the airbox!

Souns like your getting there tho, might want to have a look at the air screws too, see if they are set right.

[extonyg]

ye i thought there should of been its ok i found some to go in so thats all good now.ye i think my main problem is air leaks.
also forgot to mention there is a breather on the left hand side of the airbox is this suposed to be blocked off or open??
when you say air screws is this the same as the mixture screws?if it is mine are at 2 1/2 turns out.is this right?
thanks for your help

[RedexRobB]

The breather on the left is meant to be blocked yes, its a pipe that collects all the moisture from the airbox and has a bung in the end which needs to be emptied regularly.

Mixture screws - that sounds about what they should be

[extonyg]

sounds like some monkey has had a go at my bike before because there is no pipe on the side of my airbox its just a hole, ill block it up this weekend.slowly getting everything set up just need them carb rubbers now before i can start adjusting the needle heights and balance them up again.thanks for the help